P2B79Coolant Heater B Control Circuit Performance
- Generic OBD-II code · Powertrain
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2B79 says that coolant heater B is wired correctly but does not do what it is told: after a request the expected warming, current or status feedback fails to appear. In layouts with several stages, as in Hyundai and Kia patent US11378000B2, the controller switches the stages individually and shuts them down when outlet or housing surface temperature runs too high – a stage disabled by that protection can look like a performance fault from outside. No manufacturer documents P2B79 publicly. CARB 13 CCR 1968.2 (e)(15.2.2) demands functional checks on output components. Low coolant, trapped air, a weak heating element or an internal fault in the heater electronics are typical causes; the over-temperature code of heater A is P2DA6.
- What you may notice
- Heating power lower than expected
- Heater outlet temperature rises slowly in live data
- Fault may only appear at low outside temperatures
- Likely causes
- LikelyLow coolant or trapped air, so protection shuts the stage down
- PossibleHeating element of stage B weak or open
- PossibleInternal fault in the heater electronics for stage B
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.