P078F code meaning
Transmission Mode Switch C Circuit
What P078F means
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.
P078F at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P078F
- Drive mode (sport, winter, tow) cannot be selected
- Mode indicator missing
- Transmission stays on the normal program
Common causes of P078F
- Most likelySwitch or button faulty or sticking
- PossibleWire or connector open or shorted
- PossibleMoisture or dirt in the centre console
- Less likelyControl module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission mode switchSwitch wiringTransmission control module
What each part of P078F means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 7 | Area: transmission. |
| 8F | The exact fault in that area. |
What to do next
- Note P078F 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 P078F
What does P078F mean?
P078F means "Transmission Mode Switch C Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P078F?
P078F does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P078F fail an emissions test?
P078F is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P078F to fix?
Difficulty: easy. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P078F clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.