Engine

P01E8 — Engine Coolant Heater 'A' Control Circuit Open

Severity: low Safe to drive

What P01E8 means

The engine control module switches an electric coolant heater on through a relay or driver to warm the engine and cabin faster in cold weather. P01E8 sets when the module sees an open or fault in the control circuit for heater 'A'. Exact logic varies by vehicle, so check the manufacturer's documentation.

Symptoms

  • Check Engine light on
  • Engine takes longer to warm up
  • Weak cabin heat, especially in cold weather
  • Higher fuel use on cold starts
  • Possible emissions test failure

Possible causes

  1. Open, chafed or corroded wiring in the heater control circuit
  2. Poor contact or corrosion at the heater connector
  3. Failed coolant heater element or module
  4. Bad relay or blown fuse in the heater circuit
  5. Faulty control module or output driver (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data and look for related power or cooling codes
  2. Inspect the heater harness and connector for damage, water intrusion, corrosion and chafing
  3. Check the fuse and relay for the heater circuit
  4. Test for power and ground at the heater connector using the factory wiring diagram
  5. Check the control wire from the module to the heater for opens and shorts
  6. Measure the heater element resistance and compare it to spec
  7. Run a scan tool active test of the heater if supported
  8. If the circuit is good, test the control module or driver

Common fixes

  • Repair the wiring or replace the damaged connector
  • Replace the fuse or relay
  • Replace the coolant heater
  • Replace or reprogram the control module once it is confirmed faulty

Questions and answers

Can I drive with code P01E8?

Yes, usually. It isn't a safety risk, but warm-up will be slower and the heater weaker in the cold. Have it diagnosed soon.

What does P01E8 mean?

It means an open or fault in the control circuit of coolant heater 'A'. Wiring, connectors, the relay or the heater itself are the most common causes.

Why did P01E8 come back after repair?

A connector may have lost contact or another section of the harness may be damaged. Clear the code, run the heater active test and check the circuit under load.

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.