P078FTransmission Mode Switch C Circuit
- Generic OBD-II code · Powertrain
- How the car detects it
- P078F is the circuit fault of a third transmission mode switch (C), after A (P071A–P071C) and B (P071D–P071F): its state is invalid or implausible. GM's transmission modules of 2023 and 2025 list the number only as a blocking condition for another check, without a description of their own; GM reports its drive mode selector today under P05D0–P05D3 (8-step resistor ladder, two trips). No manufacturer document available to us describes P078F itself. The mode then cannot be selected and the transmission stays on its normal schedule.
- What you may notice
- Drive mode (sport, winter, tow) cannot be selected
- Mode indicator missing
- Transmission stays on the normal program
- Likely causes
- LikelySwitch or button faulty or sticking
- PossibleWire or connector open or shorted
- PossibleMoisture or dirt in the centre console
- RareControl module
- Repair
- Easy · Often possible to do yourself.Typical cost: €40 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.