P0D78 code meaning
A/C Compressor Control Module Output Driver Temperature Sensor Circuit Low
Powertrain system Generic code P0Dxx codes Check engine light
What P0D78 means
P0D78 is set when the output driver (IGBT) temperature sensor of the electric A/C compressor signals low, which for an NTC sensor means an implausibly hot value. GM uses 274 °C or more in the 2011–2015 Volt and the 2016 ELR, and above 150 °C in the 2016–2019 Volt; detection takes 30 of 60 samples at 50 ms, 40 of 50 at 100 ms or 4 of 5 s, Type B with MIL after two trips. Temperatures like these are beyond what the power stage survives, so a shorted sensor is more likely than real heat, although a seized compressor or a failed condenser fan can drive the IGBTs hot. Expect the A/C to switch off. The cold-side counterpart is P0D77, plausibility P0D76.
P0D78 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor1 to 5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0D78
- Check engine light after two trips
- Air conditioning switched off
Common causes of P0D78
- Most likelyShort circuit in the IGBT temperature sensor path
- Less likelyReal overheating of the power stage from high load or poor condenser cooling
- Less likelyFaulty value transmission to the host controller
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ac compressor cm output driver temp sensorAc compressor module
What each part of P0D78 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 78 | The exact fault in that area. |
What to do next
- Note P0D78 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 P0D78
What does P0D78 mean?
P0D78 means "A/C Compressor Control Module Output Driver Temperature Sensor Circuit Low". P0D78 is set when the output driver (IGBT) temperature sensor of the electric A/C compressor signals low, which for an NTC sensor means an implausibly hot value. It is a generic code, so it means the same on every make.
Is it safe to drive with P0D78?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0D78 fail an emissions test?
P0D78 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 P0D78 to fix?
Difficulty: workshop only. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P0D78 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.