Powertrain, generic · Fuel and air metering

P01E8 Engine Coolant Heater A Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Engine coolant heater A is an electric coolant heater switched by the engine module, directly or via a relay or power stage, to shorten warm-up – less cold-start emissions and faster cabin heat; A and B denote two separately switched heaters or stages. It is not the same as a mains-powered block heater (which the vehicle does not control) or the electrically heated thermostat (P0597–P0599). CARB requires output components to be checked for correct response or at least for circuit faults. This code reports an open control circuit – the module detects missing continuity, typically with the driver switched off. No manufacturer using these codes was found in the GM, Ford or NHTSA documents checked; the typical driver diagnosis (open circuit detected with the driver switched off, as GM does for other outputs) is an analogy, and thresholds are unknown.

Likely causes

Control wire or connector to the heater or relay open
Heater element burnt out or relay coil open
Fuse in the load circuit blown
Control module output stage faulty

Symptoms

  • Check engine light on
  • Longer warm-up, cabin heat slower in winter
  • Usually no change in driving

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

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

Parts involved

engine coolant heater aheater relaycontrol circuit wiring

Related codes

P01E9P01EAP01EBP01ECP0128

References: law.cornell.edu, gsi.ext.gm.com.