P2B75Coolant Heater A Control Circuit Performance
- Generic OBD-II code · Powertrain
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2B75 is set when the command circuit of coolant heater A tests electrically sound but the heater's response does not match the request – the coolant leaving it fails to warm, for instance, or reported power or current stays off target. CARB 13 CCR 1968.2 (e)(15.2.2) asks for this kind of functional check on output components. GM's bulletin PIC5943 for the 2013–2014 Volt shows the practical test: with full heat requested in electric mode the heater core temperature should climb to about 54 °C and hold; if not, early coolant heater control modules were replaced (GM stores B101D there, not P2B75). No manufacturer documents P2B75 itself. Air in the loop, weak circulation, a failed element or faulty heater electronics are typical causes.
- What you may notice
- Cabin warms slowly or only with the engine running
- Heater core temperature in live data stays low despite full heat request
- Electric range reduced in winter because the engine starts for heat
- Likely causes
- LikelyAir trapped in the heater loop or low coolant level
- PossibleHeating element weak or partly failed
- PossibleInternal fault in the heater control electronics
- RareCoolant pump or valve in the heater loop not circulating enough
- 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.