Transmission Fluid Pressure Sensor/Switch D Circuit High
What it means
P0878 sets when the "D" transmission fluid pressure sensor/switch reports an abnormally high voltage — typically an open circuit or a short to power. The controller uses this pressure reading to manage shift quality, so a bad signal can cause harsh shifts and may trigger a protective limp mode. The engine still starts and runs; this is an electrical fault in the pressure-sensing circuit rather than a mechanical failure, though fluid condition is worth checking too.
Can I keep driving? Driveable, but shifting may be harsh and the transmission may drop into limp mode; fix it promptly.
Common symptoms
What you'll notice
- Check-engine light on
- Harsh shifting or slipping
- Possible limp (fail-safe) mode
- Erratic shift timing
Common causes
Most likely first
- Open or short-to-voltage in the sensor D circuitLikely
- Failed transmission fluid pressure sensor/switch DCommon
- Corroded or loose connector at the sensorCommon
- Faulty transmission control module (less common)Less often
How to diagnose & fix
Work through it in order
- Confirm with freeze-frame data and check companion codes (P0875-P0877, P0879).
- Inspect the sensor D connector and wiring for opens or a short to power.
- Compare the sensor's signal voltage to the factory spec.
- Replace the pressure sensor/switch if the signal is stuck high.
- Check fluid level and condition, then clear the code and retest.
FAQ
Quick answers
Is it safe to drive with P0878?+
Can I just clear P0878?+
Related codes
Often seen with P0878
Read & clear P0878 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.