Cooling

P01ED — Engine Coolant Heater 'B' Control Circuit Low

Severity: low Safe to drive

What P01ED means

The PCM controls an electric coolant heater 'B' that helps the engine and cabin warm up faster in cold weather. P01ED sets when voltage in that heater's control circuit is lower than expected. Common causes are a short to ground, a failed heater element, or a wiring or connector problem.

Symptoms

  • Check Engine light on
  • Engine warms up slowly
  • Weak cabin heat in cold weather
  • Hard starting or rough running on a cold engine
  • Higher fuel consumption in cold weather

Possible causes

  1. Failed coolant heater 'B' (internal short)
  2. Control wire shorted to ground
  3. Damaged wiring harness insulation
  4. Corroded or loose connector
  5. Faulty heater relay or fuse
  6. Failed PCM output driver (rare)

How to diagnose

  1. Scan for codes and freeze frame data, and look for other heater or coolant temperature codes
  2. Inspect the heater connector and harness for damage, moisture, corrosion and chafing
  3. Check the fuse and relay that feed the heater
  4. Measure the heater element resistance and compare it with the manufacturer spec
  5. Disconnect the heater and test the control wire for a short to ground
  6. Check power supply and the PCM control signal with a multimeter or scope
  7. If wiring and heater test good, suspect the PCM and test its output

Common fixes

  • Repair or replace the damaged wiring section
  • Clean or replace the connector
  • Replace coolant heater 'B'
  • Replace a faulty relay or fuse
  • Replace or reprogram the PCM if confirmed faulty

Questions and answers

What does P01ED mean?

It means the control circuit for engine coolant heater 'B' has low voltage. The PCM usually sees a short to ground or a failed heater.

Can I drive with code P01ED?

Yes, usually. It does not harm the engine, but warm-up will be slower and cabin heat weaker in the cold, so repair it soon.

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.