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Home / DTC / P0871 — Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance

P0871 — Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance

Detailed page for trouble code P0871.

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P0871

Generic P — Powertrain

Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance

Brand: Generic
Type: P — Powertrain
Views: UK: 13 EN: 31 RU: 25
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Page language: EN

Causes

  • Faulty transmission fluid pressure sensor or pressure switch (C)
  • Open, shorted, or corroded wiring or connector in the sensor/switch C circuit
  • Poor electrical connection or terminal corrosion at connector
  • Low or contaminated transmission fluid (level/condition)
  • Internal transmission hydraulic problem (valve body, pressure regulator, blocked passage)
  • Faulty TCM/PCM or incorrect programming

Symptoms

  • Check Engine or Transmission warning light illuminated
  • Harsh, delayed, or erratic shifting
  • Transmission may go into limp-home mode (reduced gear availability)
  • Possible inability to shift or slipping under load
  • Stored P0871 code, may be accompanied by related transmission codes

What to check

  • Retrieve all stored codes and freeze frame data with a scan tool; note related transmission codes
  • Inspect transmission fluid level and condition (color, smell, contamination)
  • Visually inspect wiring and connector for sensor/switch C for damage, corrosion, or looseness
  • Backprobe sensor connector and monitor live data while cranking/running to confirm signal behavior
  • Check for continuity, short to ground, and short to battery on the sensor circuit (with ignition off)
  • Compare sensor signal (voltage/resistance) to manufacturer specification or typical expected range

Signal parameters

  • Typical variable pressure sensor: approx. 0.5–4.5 V output proportional to pressure (varies by vehicle)
  • Typical pressure switch: open/closed digital state (0 V or near-battery voltage when switched)
  • Open circuit: no signal/OL; short to ground: ~0 V; short to battery: near B+ (~12 V)
  • Expected circuit resistance to ground when disconnected depends on sensor type; consult factory spec

Diagnostic algorithm

  1. Connect an OBD-II scanner and record P0871 and any related codes and freeze-frame data. Note conditions when code set.
  2. Check transmission fluid level and condition; correct level and replace or flush if fluid is burnt/contaminated before further testing.
  3. Perform a visual inspection of the sensor/switch C connector and wiring harness for damage, chafing, or corrosion; repair as needed.
  4. Backprobe the sensor connector with the ignition on and monitor the signal while operating the transmission (or while commanded by scanner). Verify the signal type (analog voltage or digital switch) and that it changes with engine/transmission activity.
  5. With ignition off, measure continuity and resistance between sensor pin(s) and TCM connector; check for short to ground or battery. Repair wiring faults found.
  6. If wiring checks good, bench-test or replace the pressure sensor/switch C and retest. Use correct OEM or specified replacement.
  7. If replacing sensor does not clear code, inspect valve body/pressure regulator and hydraulic passages for sticking or leakage; consider professional transmission inspection.
  8. If hydraulic/mechanical components are confirmed good, verify TCM/PCM power, grounds, and update/reprogram or replace TCM only after all other causes have been eliminated.
  9. After repairs, clear codes and road-test while monitoring live data to confirm correct pressure signal and no recurrence.

Likely causes

  • Damaged wiring or loose/corroded connector to pressure sensor C
  • Failed pressure sensor/switch C
  • Low/dirty transmission fluid causing incorrect pressure
  • Valve body or pressure regulator sticking or leaking
  • Intermittent TCM input/output fault

Fault status

⚠️ Status
Stored when the transmission control module detects the Fluid Pressure Sensor/Switch C circuit output is outside expected range, inconsistent with other inputs, or shows an open/short condition.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

P0870 P0872 P0705 P0700 P0741
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