Transmission fluid pressure sensors measure the amount of hydraulic pressure inside the gearbox, then send this information to the engine control unit through a series of electrical pulses. If the ECU detects an unusually high voltage signal on the circuit for the TFPS sensor, a P0878 DTC will be saved.
How Serious is the Code?
While you may be able to get away with ignoring some transmission trouble codes, a P0878 diagnostic trouble code isn’t one of them. Whether the cause is electrical or mechanical, the potential internal damage could completely destroy your transmission.
Symptoms of a P0878 include:
- Smoke coming from the transmission
- Slipping through gears
- Transmission does not go into gear
- Low transmission fluid
- Transmission fluid is too dirty
- ATF leak
- The transmission overheats
- The engine overheats
- Wiring and/or connectors
- Malfunctioning transmission pump
- Malfunctioning transmission fluid pressure sensor
- Malfunctioning transmission fluid temperature sensor
- Malfunctioning TCM
- Internal mechanical failure
How to Diagnose the Code?
The manufacturer’s TSB database is the first place you should look when you start to diagnose a P0878 OBDII trouble code. The wiring and connectors leading to the transmission fluid pressure sensor are the second place to look, because shorted wires or corroded connectors can prevent the TFPS sensor from working. This sensor itself will also need to be checked to ensure that it is performing properly. Should no issues be found up to this point, suspect an internal mechanical problem with either the transmission pump or the valve body.
What Repairs Will Fix P0878?
- Change the transmission fluid and filter
- Repair transmission fluid leaks
- Repair or replace damaged wiring and sensors on the transmission wiring harness
- Replace the transmission pump
- Replace transmission fluid pressure sensor
- Replace transmission fluid temperature sensor
- Replace or repair valve body
- Replace or repair transmission