Engine

P037A — Glow Plug/Heater Indicator Control Circuit Low

Severity: medium Safe to drive

What P037A means

A diesel engine's ECU controls the glow plug indicator lamp and monitors the voltage in its control circuit. P037A is set when that voltage is lower than expected, for example from an open circuit, a short to ground or a failing driver. The glow plug system is usually run by a separate control module or by the ECU itself.

Symptoms

  • Check Engine light or glow plug indicator on
  • Hard starting when the engine is cold
  • Rough idle right after starting
  • White smoke at cold start
  • Slightly higher fuel consumption
  • Glow plug lamp never lights or stays on

Possible causes

  1. Open circuit or short to ground in the indicator wiring
  2. Corroded or damaged connector
  3. Faulty glow plug control module
  4. Failed glow plugs (open element)
  5. Faulty glow plug relay
  6. Instrument cluster or indicator lamp fault
  7. ECU fault (rare)

How to diagnose

  1. Scan all codes and freeze frame data and look for other glow plug codes
  2. Check whether the glow plug lamp lights up with the ignition on
  3. Inspect the harness and connectors at the glow plug module and ECU for chafing, corrosion and moisture
  4. Check supply voltage and ground at the control module and relay
  5. Measure each glow plug's resistance and compare it with the manufacturer's spec
  6. Test the indicator circuit for opens and shorts to ground using the wiring diagram
  7. Check the control module's output with a scan tool or multimeter
  8. Clear the code and confirm it does not return after a cold start

Common fixes

  • Repair the wiring and clean or replace the connectors
  • Replace the glow plug control module
  • Replace faulty glow plugs, ideally as a set
  • Replace the glow plug relay
  • Replace the instrument cluster or ECU only after confirming the fault

Questions and answers

What does P037A mean?

The ECU found low voltage in the diesel glow plug indicator control circuit. The cause is most often wiring, a connector, the control module or the glow plugs themselves.

Can I drive with code P037A?

Usually yes, especially in warm weather. In freezing temperatures the engine may start hard, so do not put the repair off 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.