Code
P1425
ALFA ROMEO
P — Powertrain
Catalytic converter 2 temperature fault
Views:
UK: 6
EN: 9
RU: 5
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P1425
FIAT
P — Powertrain
Catalytic converter 2 temperature fault
Views:
UK: 6
EN: 8
RU: 5
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P1425
KIA
P — Powertrain
EVAP Purge Control Solenoid Circuit Low Voltage
Views:
UK: 14
EN: 21
RU: 26
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P1425
Other
P — Powertrain
EGI Glow Plug Secondary Failure
Views:
UK: 14
EN: 21
RU: 23
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P1425
RAM
P — Powertrain
Register Resonant Charging 2 (RRC2)
Views:
UK: 5
EN: 9
RU: 7
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
P1425
SAAB
P — Powertrain
EVAP Canister Purge Valve, Control Module Output, Short To Ground
Views:
UK: 4
EN: 6
RU: 3
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
P1425
VOLKSWAGEN
P — Powertrain
Tank Ventilation Valve Short To Ground
Views:
UK: 14
EN: 21
RU: 27
AI status
Completed
Completed
100%
Causes
- Failed post‑catalytic converter temperature sensor (bank 2)
- Open/short or high resistance in sensor wiring or connector
- Blown sensor heater element or heater circuit fault
- Exhaust leak upstream of the sensor affecting readings
- Catalytic converter partially blocked, overheated or damaged
- ECM/PCM fault or software anomaly
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Possible reduced engine performance / limp mode (depending on vehicle strategy)
- Degraded fuel economy or rough idle (less common)
- Exhaust odor, catalytic rattle, or overheating smell in severe catalytic damage cases
- Stored P1425 (and possibly related codes) in ECU memory
What to check
- Read and record all stored codes and freeze‑frame data with a diagnostic scanner
- Capture live data: upstream and downstream catalyst temperature sensors, oxygen sensors, heater status and fuel trims
- Visual inspection of sensor, wiring harness and connector for heat damage, corrosion or disconnection
- Check for exhaust leaks (manifold, gasket, flange, pipe) upstream of the sensor
- Inspect catalytic converter for physical damage, rattling or signs of overheating
- Verify battery and charging system voltage (low voltage can affect heater circuits)
Signal parameters
- Sensor type: thermistor/temperature sensor with voltage or resistance output (refer to model service info)
- Typical signal range: 0–5.0 V (many temp sensors output a voltage proportional to temp)
- Thermistor resistance at 20–25 °C commonly in the ~1–10 kΩ range (manufacturer dependent)
- Heater circuit: expected supply voltage ~12 V when active; heater element resistance typically low (single‑digit to low tens of ohms) — consult factory specs
- Normal behavior: downstream (post‑cat) temp rises more slowly and is lower than upstream temp once converter is warmed; a persistent much higher or lower downstream value compared with upstream is abnormal
- ECM trigger condition: downstream sensor out of expected range or not following upstream temperature profile (specific thresholds are manufacturer defined)
Diagnostic algorithm
- Verify code and related codes (oxygen sensors, heater circuits, catalytic efficiency). Note freeze‑frame values. 2) Perform a careful visual inspection of the downstream (post‑cat) temperature sensor and wiring: look for heat damage, melted insulation, pin corrosion, broken wires or poor connector fit. 3) With a capable scan tool, monitor live upstream and downstream catalyst temperatures and sensor heater status while cold start and during warm‑up. Note whether both sensors respond and the heater is commanded ON. 4) Backprobe sensor connector with multimeter/scan tool: check sensor supply (12 V when heater commanded), ground continuity, and signal voltage/resistance. Compare measured values to factory specs. 5) Measure heater element resistance (unplugged): verify it is within spec and not open. Check for short to ground. 6) If wiring checks fail intermittently, perform wiggle test and recheck live data to reproduce. 7) Check for exhaust leaks upstream of the sensor and repair if found; leaks can cause false temperature readings. 8) If sensor wiring and heater are good, compare upstream vs downstream temperature pattern under load (accelerate or road test) — a downstream sensor that remains much colder or hotter than expected can indicate sensor failure or catalytic converter problem. 9) If sensor is faulty by bench/ohm/voltage testing or does not change with temperature, replace the sensor and clear codes. 10) After repair, erase codes and perform a full drive cycle / readiness verification. If fault returns, progress to catalytic converter inspection/replacement or ECU diagnostics per factory procedures.
Likely causes
- Sensor heater failed or heater circuit open/short
- Damaged wiring harness at heat/exhaust area (chafing, melted insulation)
- Connector corrosion or poor earth/ground to sensor circuit
- Catalyst overheating or impaired flow changing temperature profile
- Exhaust leak between catalyst and sensor producing false temperature reading
Fault status
Status
ECM detected abnormal/incorrect signal from catalytic converter 2 temperature sensor circuit (post‑catalyst). Circuit may be open, shorted, heater faulty, or catalytic temperature profile outside expected range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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