Engine

P0384 — Glow Plug Control Module 1 Control Circuit High

Severity: medium Drive with care, to a shop

What P0384 means

P0384 means the diesel engine's control unit detected a high signal, either excess voltage or a short to power, in the control circuit of glow plug control module 1. Normally the module switches current to the glow plugs on the ECU's command to warm the combustion chambers before and after startup. A fault in this circuit disrupts that heating control.

Symptoms

  • Glow plug or check engine light on
  • Long cranking before the engine starts
  • Hard cold starts
  • Rough idle until the engine warms up
  • White smoke at cold start
  • Increased emissions

Possible causes

  1. Faulty glow plug control module or relay
  2. Damaged or shorted wiring or connectors, including a short to positive
  3. Defective glow plugs putting abnormal load on the circuit
  4. Low battery voltage or charging system problems
  5. Internal ECU fault (uncommon)

How to diagnose

  1. Read codes and freeze frame data and look for other glow plug or power supply codes
  2. Test battery voltage and alternator output
  3. Inspect the module wiring and connectors for chafing, corrosion or heat damage
  4. Check the fuses and relay in the glow plug circuit
  5. Check supply, ground and the control signal from the ECU at the module with a multimeter
  6. Measure each glow plug's resistance and compare to spec
  7. Test the control wire for a short to power
  8. If the circuit is good, suspect the module first and the ECU last

Common fixes

  • Replace the glow plug control module or relay
  • Repair or replace damaged wiring and connectors
  • Replace faulty glow plugs
  • Service or replace the battery and fix any charging problem

Questions and answers

Can I drive with a P0384 code?

Usually yes, but cold starts will be hard and the engine may smoke. Get it diagnosed soon so the module or wiring isn't damaged further.

What most often causes P0384?

Most often it is a failed control module or relay, or damaged wiring shorted to power. Bad glow plugs or a weak battery are less common causes.

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.