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Home / DTC / P0845 — Transmission Control Module (TCM) failure, Transmission fluid level is low, Transmission fluid pressure sensor failure, Wiring issue

P0845 — Transmission Control Module (TCM) failure, Transmission fluid level is low, Transmission fluid pressure sensor failure, Wiring issue

Detailed page for trouble code P0845.

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Code

P0845

AUDI P — Powertrain

Transmission Control Module (TCM) failure, Transmission fluid level is low, Transmission fluid pressure sensor failure, Wiring issue

Brand: AUDI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Low or contaminated transmission fluid level
  • Faulty transmission fluid pressure sensor/switch
  • Open/short/corroded wiring or poor connector/ground to sensor
  • Internal transmission hydraulic problem (clogged valve/screen, internal leak)
  • TCM software fault or module failure

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Transmission enters limp/diagnostic mode or limits gear selection
  • Harsh, delayed, or erratic shifting
  • Transmission slipping or inability to hold gear
  • Transmission temperature warning or unusual noise in severe cases

What to check

  • Read and record freeze frame and pending codes with a capable scan tool
  • Check transmission fluid level, color and smell; confirm correct fluid and service interval
  • Visually inspect sensor connector and harness for corrosion, damage, pin push-out or water intrusion
  • Scan live data: monitor transmission fluid pressure sensor voltage and related parameters while key ON and during gear changes
  • Check for related codes (TCM, speed sensors, grounds) and consult manufacturer service information/TSBs
  • Perform wiggle/rock test on harness while observing live data for intermittent changes

Signal parameters

  • Sensor reference: typical 5 V reference from TCM (verify with manufacturer data)
  • Signal voltage: commonly in the ~0.5–4.5 V range proportional to pressure (varies by model; check AUDI spec)
  • Signal behavior: voltage should change smoothly with gear changes/load; stuck, spiking, or constant values indicate fault
  • Circuit resistance: check harness continuity to TCM and resistance to ground per OEM specs

Diagnostic algorithm

  1. Connect scan tool, record codes, freeze frame and live data; note conditions when fault set
  2. Consult manufacturer service information and TSBs for known faults or required software updates to the TCM
  3. Check and, if necessary, correct transmission fluid level and condition; top or change fluid and filter if contaminated
  4. Perform visual inspection of sensor, connector and harness; repair any corrosion, frayed wires or poor grounds
  5. Back-probe sensor connector: with ignition ON (engine OFF) verify reference voltage (~5V), ground continuity, and monitor signal voltage while an assistant cycles selector or starts engine; compare to expected behavior
  6. If signal is out-of-range, check continuity and shorts between sensor and TCM; repair wiring as needed
  7. If wiring and connector good but signal still invalid, perform a mechanical transmission pressure test with a calibrated gauge to confirm actual hydraulic pressure
  8. If mechanical pressure and sensor signal disagree, replace the pressure sensor and retest
  9. Clear codes and perform a road test and re-scan. If code returns and wiring/sensor verified, consider TCM diagnostics/software reflash or replacement per OEM procedures
  10. Document repairs and verify no additional codes remain before returning vehicle to service

Likely causes

  • Low fluid level or incorrect fluid type
  • Corroded or loose sensor connector or damaged harness
  • Faulty pressure sensor producing no or incorrect voltage signal
  • Intermittent contact or short to +12V/ground in sensor circuit
  • TCM input circuit failure or incorrect calibration

Fault status

⚠️ Status
P0845 — Transmission pressure sensor circuit out-of-range. Possible low fluid, sensor or wiring fault; verify fluid, inspect wiring/connectors, compare sensor signal to mechanical pressure, and continue diagnosis.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.5 hours

Similar codes

P0700 P0715 P0720 P0840 P0841
Repair manuals

Manual library for AUDI

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Code

P0845

Generic P — Powertrain

Transmission Fluid Pressure Sensor/Switch B Circuit

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Low or contaminated transmission fluid level
  • Faulty transmission fluid pressure sensor/switch
  • Open/short/corroded wiring or poor connector/ground to sensor
  • Internal transmission hydraulic problem (clogged valve/screen, internal leak)
  • TCM software fault or module failure

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Transmission enters limp/diagnostic mode or limits gear selection
  • Harsh, delayed, or erratic shifting
  • Transmission slipping or inability to hold gear
  • Transmission temperature warning or unusual noise in severe cases

What to check

  • Read and record freeze frame and pending codes with a capable scan tool
  • Check transmission fluid level, color and smell; confirm correct fluid and service interval
  • Visually inspect sensor connector and harness for corrosion, damage, pin push-out or water intrusion
  • Scan live data: monitor transmission fluid pressure sensor voltage and related parameters while key ON and during gear changes
  • Check for related codes (TCM, speed sensors, grounds) and consult manufacturer service information/TSBs
  • Perform wiggle/rock test on harness while observing live data for intermittent changes

Signal parameters

  • Sensor reference: typical 5 V reference from TCM (verify with manufacturer data)
  • Signal voltage: commonly in the ~0.5–4.5 V range proportional to pressure (varies by model; check AUDI spec)
  • Signal behavior: voltage should change smoothly with gear changes/load; stuck, spiking, or constant values indicate fault
  • Circuit resistance: check harness continuity to TCM and resistance to ground per OEM specs

Diagnostic algorithm

  1. Connect scan tool, record codes, freeze frame and live data; note conditions when fault set
  2. Consult manufacturer service information and TSBs for known faults or required software updates to the TCM
  3. Check and, if necessary, correct transmission fluid level and condition; top or change fluid and filter if contaminated
  4. Perform visual inspection of sensor, connector and harness; repair any corrosion, frayed wires or poor grounds
  5. Back-probe sensor connector: with ignition ON (engine OFF) verify reference voltage (~5V), ground continuity, and monitor signal voltage while an assistant cycles selector or starts engine; compare to expected behavior
  6. If signal is out-of-range, check continuity and shorts between sensor and TCM; repair wiring as needed
  7. If wiring and connector good but signal still invalid, perform a mechanical transmission pressure test with a calibrated gauge to confirm actual hydraulic pressure
  8. If mechanical pressure and sensor signal disagree, replace the pressure sensor and retest
  9. Clear codes and perform a road test and re-scan. If code returns and wiring/sensor verified, consider TCM diagnostics/software reflash or replacement per OEM procedures
  10. Document repairs and verify no additional codes remain before returning vehicle to service

Likely causes

  • Low fluid level or incorrect fluid type
  • Corroded or loose sensor connector or damaged harness
  • Faulty pressure sensor producing no or incorrect voltage signal
  • Intermittent contact or short to +12V/ground in sensor circuit
  • TCM input circuit failure or incorrect calibration

Fault status

⚠️ Status
P0845 — Transmission pressure sensor circuit out-of-range. Possible low fluid, sensor or wiring fault; verify fluid, inspect wiring/connectors, compare sensor signal to mechanical pressure, and continue diagnosis.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.5 hours

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P0700 P0715 P0720 P0840 P0841
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Code

P0845

MERCEDES-BENZ P — Powertrain

Trans Fluid Press Sensor/Switch B Circuit Malfunction

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Low or contaminated transmission fluid level
  • Faulty transmission fluid pressure sensor/switch
  • Open/short/corroded wiring or poor connector/ground to sensor
  • Internal transmission hydraulic problem (clogged valve/screen, internal leak)
  • TCM software fault or module failure

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Transmission enters limp/diagnostic mode or limits gear selection
  • Harsh, delayed, or erratic shifting
  • Transmission slipping or inability to hold gear
  • Transmission temperature warning or unusual noise in severe cases

What to check

  • Read and record freeze frame and pending codes with a capable scan tool
  • Check transmission fluid level, color and smell; confirm correct fluid and service interval
  • Visually inspect sensor connector and harness for corrosion, damage, pin push-out or water intrusion
  • Scan live data: monitor transmission fluid pressure sensor voltage and related parameters while key ON and during gear changes
  • Check for related codes (TCM, speed sensors, grounds) and consult manufacturer service information/TSBs
  • Perform wiggle/rock test on harness while observing live data for intermittent changes

Signal parameters

  • Sensor reference: typical 5 V reference from TCM (verify with manufacturer data)
  • Signal voltage: commonly in the ~0.5–4.5 V range proportional to pressure (varies by model; check AUDI spec)
  • Signal behavior: voltage should change smoothly with gear changes/load; stuck, spiking, or constant values indicate fault
  • Circuit resistance: check harness continuity to TCM and resistance to ground per OEM specs

Diagnostic algorithm

  1. Connect scan tool, record codes, freeze frame and live data; note conditions when fault set
  2. Consult manufacturer service information and TSBs for known faults or required software updates to the TCM
  3. Check and, if necessary, correct transmission fluid level and condition; top or change fluid and filter if contaminated
  4. Perform visual inspection of sensor, connector and harness; repair any corrosion, frayed wires or poor grounds
  5. Back-probe sensor connector: with ignition ON (engine OFF) verify reference voltage (~5V), ground continuity, and monitor signal voltage while an assistant cycles selector or starts engine; compare to expected behavior
  6. If signal is out-of-range, check continuity and shorts between sensor and TCM; repair wiring as needed
  7. If wiring and connector good but signal still invalid, perform a mechanical transmission pressure test with a calibrated gauge to confirm actual hydraulic pressure
  8. If mechanical pressure and sensor signal disagree, replace the pressure sensor and retest
  9. Clear codes and perform a road test and re-scan. If code returns and wiring/sensor verified, consider TCM diagnostics/software reflash or replacement per OEM procedures
  10. Document repairs and verify no additional codes remain before returning vehicle to service

Likely causes

  • Low fluid level or incorrect fluid type
  • Corroded or loose sensor connector or damaged harness
  • Faulty pressure sensor producing no or incorrect voltage signal
  • Intermittent contact or short to +12V/ground in sensor circuit
  • TCM input circuit failure or incorrect calibration

Fault status

⚠️ Status
P0845 — Transmission pressure sensor circuit out-of-range. Possible low fluid, sensor or wiring fault; verify fluid, inspect wiring/connectors, compare sensor signal to mechanical pressure, and continue diagnosis.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.5 hours

Similar codes

P0700 P0715 P0720 P0840 P0841
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MERCEDES-BENZ

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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