OBD-II code · Powertrain (generic, extended)
P2B78 Coolant Heater B Control Circuit High
The control circuit of coolant heater B reports a control circuit high condition. Auxiliary preheating of the coolant cannot be commanded as expected.
Is it safe to drive with P2B78?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl wire shorted to B+
- PossibleOpen heater element
- Less likelyConnector pins corroded - high contact resistance
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Usually unaffected
- Parts involved
- Coolant Heater B, Wiring Harness, Ecm
Related codes
- P2B74Coolant Heater A Control Circuit High
- P2B75Coolant Heater A Control Circuit Performance
- P2B76Coolant Heater B Control Circuit/Open
- P2B77Coolant Heater B Control Circuit Low
- P2B79Coolant Heater B Control Circuit Performance
- P2B7AEVAP System Pressure Sensor/Switch C Circuit
- P2B7BEVAP System Pressure Sensor/Switch C Circuit Range/Performance
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.