P0870 code meaning
Transmission Fluid Pressure Sensor/Switch C Circuit
Powertrain system Generic code P08xx codes Check engine light
What P0870 means
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.
P0870 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0870
- MIL or transmission warning lamp on
- Limp mode with a fixed gear
- Harsh or missing shifts
Common causes of P0870
- Most likelyPressure switch C faulty (sticking, seal leaking)
- PossibleSticking shift valve or worn valve body bore
- PossibleWiring or connector at the gearbox
- Less likelyControl module software (Ram 68RFE)
- Less likelyLow fluid level
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission fluid pressure sensorTransmission valve bodyTransmission wiringTransmission control module
What each part of P0870 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 70 | The exact fault in that area. |
What to do next
- Note P0870 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0870
What does P0870 mean?
P0870 means "Transmission Fluid Pressure Sensor/Switch C Circuit". Transmission fluid pressure switches C and D report whether a clutch circuit is pressurised. It is a generic code, so it means the same on every make.
Is it safe to drive with P0870?
Drive gently and only to a workshop. With P0870 the car can go into limp mode (reduced power) to protect itself.
Will P0870 fail an emissions test?
Yes, it can. P0870 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0870 to fix?
Difficulty: hard. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will P0870 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.