Powertrain, generic (extended)

P2E78 Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Loose or fretting terminal in the sensor D connector
Harness rubbing through near moving or vibrating parts
False detection by controller software (update)

Symptoms

  • Warning light that comes and goes
  • Coolant temperature in live data jumping

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–600
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv battery pack coolant temp sensor dwiring harnessbms

Related codes

P2E74P2E75P2D56P0CD9P0C46

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.