What does code P2B78 mean?

Q: What does code P2B78 mean?

Coolant Heater B Control Circuit High. P2B78 indicates that the powertrain control module has detected a high voltage condition on the control circuit for coolant heater B, which is typically a heater element used to warm engine coolant for faster cabin heat or emissions reduction. The computer expects a certain voltage range on the control circuit but sees a voltage that is higher than normal, often near battery voltage, indicating an open circuit or a short to voltage.

DTC codes / P2Bxx · Hybrid propulsion / P2B78

P2B78Coolant Heater B Control Circuit High

P2B78 indicates that the powertrain control module has detected a high voltage condition on the control circuit for coolant heater B, which is typically a heater element used to warm engine coolant for faster cabin heat or emissions reduction. The computer expects a certain voltage range on the control circuit but sees a voltage that is higher than normal, often near battery voltage, indicating an open circuit or a short to voltage.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaHybrid propulsion

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.