Powertrain, generic (extended)

P2B75 Coolant Heater A Control Circuit Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Air trapped in the heater loop or low coolant level
Heating element weak or partly failed
Internal fault in the heater control electronics
Coolant pump or valve in the heater loop not circulating enough

Symptoms

  • 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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,500
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant heater awiring harnessecm

Related codes

P2B72P2B79P2DA4P2DA6P01EB

References: law.cornell.edu, static.nhtsa.gov, patents.google.com.