Engine

P038A — Glow Plug Circuit C Malfunction

Severity: medium Safe to drive

What P038A means

P038A means the engine control module or glow plug control module detected a problem in glow plug circuit C. This is typically one bank, group or channel of glow plugs that is monitored separately. The glow plug system heats the combustion chambers so a cold diesel starts easily and runs cleanly. The module watches current and voltage in each circuit and sets the code when they fall outside the expected range.

Symptoms

  • Check Engine light on
  • Hard starting, especially in cold weather
  • Long cranking time
  • White or gray smoke and rough running on warm-up
  • Glow plug indicator stays on longer or flashes
  • Increased emissions

Possible causes

  1. Failed glow plug (or several) in circuit C
  2. Open, short or corroded wiring and connectors in circuit C
  3. Faulty glow plug relay or glow plug control module
  4. Blown fuse in the circuit
  5. Rarely, a faulty engine control module

How to diagnose

  1. Scan all codes and freeze frame data, and look for other glow plug codes
  2. Inspect the harness, connectors and plug terminals for damage, oil and corrosion
  3. Check the fuse and the power supply to the relay or control module
  4. Measure each glow plug's resistance with a multimeter and compare it to specification
  5. Test the circuit for opens and shorts to ground or power between the module and the plugs
  6. Check glow plug current draw with a current clamp or scan tool data if supported
  7. Command the relay or module with a scan tool to confirm it responds
  8. If everything else tests good, evaluate the ECM and its software

Common fixes

  • Replace failed glow plugs, preferably as a set if they are worn
  • Repair damaged wiring, connectors and terminals
  • Replace the glow plug relay or control module
  • Replace a blown fuse after finding what overloaded it
  • Update software or repair the ECM if all else is sound

Questions and answers

Can I drive with a P038A code?

Usually yes, especially in warm weather. Once it gets cold, starting can become a problem, so don't put the repair off for long.

What does the letter C mean in the circuit name?

It labels one of the glow plug circuits or groups. Which cylinders it covers depends on the manufacturer, so check the wiring diagram for your vehicle.

Is replacing the glow plugs enough to fix it?

Not always. Measure the plugs first and check the wiring, fuse and relay, or the new plugs may fail again.

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.