Home / DTC / P1199 — Radiator Temperature Sensor Voltage Too Low

P1199 — Radiator Temperature Sensor Voltage Too Low

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Code

P1199

DODGE P — Powertrain

Radiator Temperature Sensor Voltage Too Low

Brand: DODGE
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P1199

JAGUAR P — Powertrain

Fuel Level Input Circuit Low

Brand: JAGUAR
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P1199

JEEP P — Powertrain

Radiator Temperature Sensor Voltage Too Low

Brand: JEEP
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P1199

LAND ROVER P — Powertrain

Low fuel level sensor input

AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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Code

P1199

Other P — Powertrain

Fuel Level Input Circuit Low

Brand: Other
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

7,181

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Code

P1199

PLYMOUTH P — Powertrain

Radiator Temperature Sensor Voltage Too Low

Brand: PLYMOUTH
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P1199

PONTIAC P — Powertrain

Radiator Temperature Sensor Voltage Too Low

Brand: PONTIAC
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

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Code

P1199

RAM P — Powertrain

Radiator Temperature Sensor Input voltage too low

Brand: RAM
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

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Code

P1199

VOLKSWAGEN P — Powertrain

Oxygen Sensor Heater Circuit Bank 2 Sensor 2 Electrical Malfunction

AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed radiator temperature sensor (thermistor)
  • Short to ground in the sensor signal wire
  • Open or high-resistance wiring/connector (poor pin contact, corrosion)
  • Lost or low reference voltage from the ECM
  • Poor ground at sensor or ECM
  • Coolant-related damage to sensor (contamination, corrosion)

Symptoms

  • Check Engine Light (MIL) illuminated
  • Cooling fan(s) may run continuously or not run when expected
  • Erratic or incorrect coolant temperature gauge reading
  • Possible poor idle or drivability issues under temperature-related conditions
  • Reduced engine performance or limp functionality if ECM limits systems due to invalid temp input

What to check

  • Retrieve freeze frame data and stored/MIL history for P1199 and any related DTCs
  • Visually inspect radiator area wiring, connectors, and sensor for damage or corrosion
  • Check connector pins for corrosion, bent pins, or water intrusion
  • Scan live data: monitor radiator temp sensor voltage and coolant temperature reading while key on and during engine warm-up
  • Verify battery voltage and grounds before testing sensors (voltage
  • Backprobe sensor connector and wiggle wiring while monitoring live data for intermittent faults

Signal parameters

  • Sensor type: thermistor (NTC style) — resistance decreases as temperature increases
  • Circuit: 3-wire or 2-wire arrangement depending on application — typically signal, ground, and sometimes a 5 V reference
  • Expected reference: nominal 5 V reference from ECM (verify spec for vehicle)
  • Expected signal voltage range: ~0.1–4.9 V depending on temperature (cold = higher voltage, hot = lower voltage for NTC)
  • Typical behavior: as coolant warms, sensor voltage falls and calculated temperature rises

Diagnostic algorithm

  1. Verify P1199 is current and note freeze-frame and any additional DTCs. Clear codes and re-run if intermittent.
  2. Perform visual inspection of radiator area wiring, harness clamps, and sensor connector. Repair any obvious damage or corrosion.
  3. With ignition ON (engine off) monitor sensor voltage via scan tool. Check for stable 5 V reference (if equipped) and good ground at connector.
  4. Backprobe the signal wire and wiggle the harness while watching live data for voltage drops or erratic changes.
  5. Measure sensor resistance at ambient and while heating with warm coolant or hot water (engine cold, then warm carefully). Compare resistance to OEM chart; NTC sensors show decreasing resistance as temperature increases.
  6. If signal is very low (near 0 V) and reference is present, check for short to ground in the signal wire: disconnect sensor and measure continuity from signal pin to chassis ground.
  7. Check continuity from sensor connector to ECM connector and verify pin-to-pin resistance and proper grounding.
  8. Repair wiring/connectors or replace sensor if out of spec. After repairs, clear codes and perform drive cycle to verify code does not return.
  9. Only consider ECM replacement after all wiring and sensor checks are confirmed good and bench/bench/vehicle tests indicate ECM failure.

Likely causes

  • Damaged sensor connector or corroded pins
  • Broken or chafed signal wire shorting to chassis ground
  • Failed temperature sensor (internal short or open)
  • Bad ground at radiator/sensor mounting point
  • Blown fuse or ECM reference output fault

Fault status

⚠️ Status
Radiator temperature sensor voltage below expected threshold. ECM detected a low-voltage input on the radiator temp sensor circuit (possible short to ground, open reference, or sensor failure). May cause incorrect temp readings and affect cooling fan control. Code stored and MIL may illuminate.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

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