P2B77
Coolant Heater B Control Circuit Low
The control circuit of coolant heater B reports a control circuit low condition. Auxiliary preheating of the coolant cannot be commanded as expected.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Control wire shorted to groundCommon
- Heater element shortedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Coolant Heater B
- Wiring Harness
- ECM
P2B77 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.