P0871Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Transmission fluid pressure switches C and D report whether a clutch circuit is pressurised. They are more widespread than A and B: GM's 6L80/6L90 and 6T40/6T70 six-speeds put switch C on the 2-6 brake and D on the 1-2-3-4 clutch, Allison uses them for its third shift valve and its reverse switch, Ram's RFE gearboxes for the clutch pressure switches in the solenoid block. Ford reports pressure faults under its solenoid codes. P0871 means the switch does not follow the command or gear. On Ram's RFE it is the overdrive clutch switch: open in gears 1 to 3, closed in 4 to 6; it closes at about 1.5 bar and opens at 0.75 bar. Sonnax blames worn valve body bores in about 90 % of cases; on 2024 trucks it came with P0868 from a broken rear thrust washer. Allison 2006: switch without pressure 5 s after command, type A.
- What you may notice
- MIL or transmission warning lamp on
- Limp mode, often in 2nd or 3rd gear
- Harsh engagement, neutral feeling in 4th gear
- Likely causes
- LikelyWorn valve body bores or shift valve plugs
- PossibleMechanical damage: thrust washer, clutch seals
- PossiblePressure switch faulty (lip seal)
- PossibleDirt or sticking valve (dual clutch)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €200 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.