Cooling

P01EC — Engine Coolant Heater B Control Circuit Open

Severity: low Safe to drive

What P01EC means

The engine control module switches an electric coolant heater on and off, usually through a relay or driver, and monitors the control circuit. P01EC sets when the ECM sees an open circuit or no expected signal in the heater B control circuit. These heaters help the engine and cabin warm up faster in cold weather, so the problem is most noticeable in winter.

Symptoms

  • Check Engine light on
  • Slow engine and cabin warm-up in cold weather
  • Heater blows cold air for a long time
  • Slightly higher fuel use during warm-up
  • Coolant heater does not turn on or works intermittently

Possible causes

  1. Open or broken wire in the heater B control circuit
  2. Corroded or loose connector terminals
  3. Failed engine coolant heater B
  4. Bad relay or blown fuse feeding the heater
  5. Rarely, a faulty engine control module

How to diagnose

  1. Scan all codes and review freeze frame data, looking for other cooling or power supply codes
  2. Inspect the heater wiring and connector for damage, moisture, corrosion or chafed insulation
  3. Check the fuse and relay that power the heater
  4. Verify power and ground at the connector using the factory wiring diagram
  5. Test the control wire from the ECM to the heater for opens and shorts
  6. Measure the heater resistance and compare it to specification
  7. Command the heater on with a scan tool, if supported, and confirm it heats up
  8. If the circuit is good, evaluate the ECM and check for software updates

Common fixes

  • Repair the broken wire or replace the damaged connector
  • Clean or replace corroded terminals
  • Replace the relay or fuse
  • Replace the engine coolant heater B
  • Replace or reprogram the ECM (rare)

Questions and answers

Can I drive with P01EC?

Usually yes. The main effect is slower warm-up of the engine and cabin. If the temperature rises or other codes appear, get it checked promptly.

What most often causes P01EC?

Most often it is a broken wire, a poor connector contact or a failed heater. Start with the wiring, fuse and relay.

Will clearing P01EC fix it?

Clearing the code only turns the light off. While the open circuit remains, the code will return after the next circuit test, so find and fix the cause first.

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.