Engine

P037B — Glow Plug Indicator Lamp Control Circuit High

Severity: medium Safe to drive

What P037B means

The engine control module (or a separate glow plug control module) switches the glow plug indicator lamp on the dash through a control circuit. P037B sets when the voltage in that circuit is higher than expected, for example from a short to voltage, damaged wiring or a failed driver inside the module. The circuit is monitored every time the ignition is turned on.

Symptoms

  • Check engine light or glow plug indicator on
  • Glow plug lamp behaves oddly: stays on, stays off or flashes
  • Hard starting on a cold diesel
  • White smoke at cold start
  • Rough running right after a cold start

Possible causes

  1. Short to voltage in the lamp control circuit
  2. Damaged wiring or corroded, loose connectors
  3. Faulty glow plug control module
  4. Faulty glow plug relay
  5. Failed glow plugs (one or more open circuit)
  6. Internal fault in the engine control module

How to diagnose

  1. Scan all codes and freeze frame data, and note any other glow plug codes
  2. Watch how the glow plug lamp behaves when the ignition is turned on
  3. Inspect the harness and connectors at the glow plug module, ECM and relay for chafing, moisture and corrosion
  4. Check power and ground supply to the glow plug control module
  5. Measure voltage on the lamp control circuit with the ignition on and compare with the wiring diagram
  6. Test the control wire for a short to voltage and for an open circuit
  7. Measure each glow plug's resistance and test the relay
  8. If the wiring is good, test the glow plug module and then the ECM

Common fixes

  • Repair or replace damaged wiring and connectors
  • Replace a faulty glow plug relay
  • Replace failed glow plugs
  • Replace the glow plug control module
  • Reflash or replace the ECM if an internal fault is confirmed

Questions and answers

What does code P037B mean?

It means high voltage in the glow plug indicator lamp control circuit. The control unit sees more voltage than expected, most often from a short to voltage or a faulty control module.

Can I drive with P037B?

Usually yes, especially in warm weather. However, if the glow plugs are not working, cold starts can get difficult, so don't put off diagnosis for long.

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.