P2E78 code meaning
Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic
Powertrain system Generic code P2Exx codes Check engine light
What P2E78 means
P2E78 stands for a coolant temperature from sensor D that jumps around, mostly without leaving the electrical limits. A liquid loop changes temperature slowly, so fast swings point to a loose contact rather than to the coolant. No manufacturer documents P2E78 publicly. GM's 2019 hybrid table shows a matching test for inlet sensor A (P0C46): it adds up the absolute changes between ten successive readings and counts a sum above 64 °C as a fail; 4 s out of 5 s set a two-trip Type B code, and it is skipped while the hard faults P0C44/P0C45 are present. Volvo found that P0CD900 for sensor B on 2021–22 PHEVs after charging in warm weather might be a spurious entry; software release 3.2.4 resolves it (TJ 36929). CARB requires circuit continuity monitoring.
P2E78 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of P2E78
- Warning light that comes and goes
- Coolant temperature in live data jumping
Common causes of P2E78
- Most likelyLoose or fretting terminal in the sensor D connector
- PossibleHarness rubbing through near moving or vibrating parts
- Less likelyFalse detection by controller software (update)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery pack coolant temp sensor dWiring harnessBms
What each part of P2E78 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 78 | The exact fault in that area. |
What to do next
- Note P2E78 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 P2E78
What does P2E78 mean?
P2E78 means "Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic". P2E78 stands for a coolant temperature from sensor D that jumps around, mostly without leaving the electrical limits. It is a generic code, so it means the same on every make.
Is it safe to drive with P2E78?
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 P2E78 fail an emissions test?
Yes, it can. P2E78 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2E78 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P2E78 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.