P0870Transmission Fluid Pressure Sensor/Switch C Circuit
- 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. P0870 is the general fault. Allison's 2006 table uses it for the switch on valve S3: if it reports pressure for more than 20 ms with the valve at rest, the valve is retried twice and the case classed as electrical, mechanical or sporadic, type A. Ram corrected false P0870 'hydraulic pressure tests' on the 2019 68RFE with a software update.
- What you may notice
- MIL or transmission warning lamp on
- Limp mode with a fixed gear
- Harsh or missing shifts
- Likely causes
- LikelyPressure switch C faulty (sticking, seal leaking)
- PossibleSticking shift valve or worn valve body bore
- PossibleWiring or connector at the gearbox
- RareControl module software (Ram 68RFE)
- RareLow fluid level
- 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: €100 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.