Cooling

P01F8 — Engine Coolant Heater A Control Circuit Current or Temperature Too High

Severity: low Safe to drive

What P01F8 means

The electric engine coolant heater "A" is switched on by the control module through an output driver to speed up warm-up of the engine and cabin. P01F8 sets when the module sees too much current or too high a driver temperature in that control circuit. Common causes are a wiring short, a failing heater or a faulty driver.

Symptoms

  • Check Engine light on
  • Slow engine and cabin warm-up, especially in cold weather
  • Heater blows lukewarm air for a long time
  • Higher fuel consumption on cold starts
  • Other codes for the heater circuit or coolant temperature sensor may appear

Possible causes

  1. Failed coolant heater (internal short)
  2. Wiring harness shorted to battery voltage or ground
  3. Corroded or damaged connectors, or high resistance in the circuit
  4. Faulty driver inside the PCM or a separate heater control module
  5. Less often, a faulty coolant temperature sensor upsetting the control logic

How to diagnose

  1. Scan all codes and freeze frame data, clear the code and see if it returns
  2. Check the fuse and relay for the heater circuit
  3. Inspect the harness and heater connector for chafing, heat damage and corrosion
  4. Test the control and power wires for shorts to ground or voltage and for opens
  5. Measure heater resistance and compare it with the spec for your vehicle
  6. Check supply voltage and the control signal at the connector when the heater is commanded on
  7. Compare coolant temperature sensor readings with actual engine temperature
  8. If wiring and heater are good, test the control module or PCM driver

Common fixes

  • Repair or replace damaged wiring and connectors
  • Replace the engine coolant heater
  • Replace the heater control module or repair the PCM driver
  • Replace the coolant temperature sensor if it is confirmed faulty
  • Replace a blown fuse only after the cause of the short is fixed

Questions and answers

Can I drive with code P01F8?

Usually yes, since there is no serious threat to the engine. Warm-up will be poorer, though, and the circuit fault should be fixed to avoid damaging the driver or wiring.

What most often causes P01F8?

Most often it is a short in the wiring or an internal fault in the heater itself. Start with the fuse and a visual check of the connectors.

Do I need to replace the PCM for P01F8?

Usually not. Check the wiring, connectors and the heater first. A failed driver inside the module is less common.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.