Engine

P038E — Glow Plug Heater Circuit 'B' Control Signal Low

Severity: medium Drive with care, to a shop

What P038E means

The engine control unit switches the glow plugs on through a relay or control module and monitors voltage and current in circuit 'B'. P038E sets when the control signal in that circuit is lower than expected or the circuit does not respond properly. The cause can be the glow plugs, the control module, wiring or connectors.

Symptoms

  • Check engine light or glow plug indicator on
  • Hard starting, especially when cold
  • Rough idle or misfires
  • White or gray smoke after start-up
  • Hesitation, and rarely stalling

Possible causes

  1. Wiring harness damage: shorts, opens or corroded terminals
  2. Failed glow plugs or heating element in circuit 'B'
  3. Faulty glow plug control module or relay
  4. Poor ground or power supply, or weak battery voltage
  5. Faulty crankshaft or camshaft position sensor (uncommon)
  6. Faulty ECM (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data, and look for other glow plug codes
  2. Test battery condition and cranking voltage, and inspect terminals and grounds
  3. Inspect the harness and the glow plug and module connectors for damage, corrosion or heat marks
  4. Measure resistance of each glow plug with a multimeter and compare to spec
  5. Check for power and a control signal at the module or relay
  6. Test the control wire between the ECM and module for opens and shorts to ground
  7. Run a scan tool active test on the module if supported
  8. Suspect the ECM only after everything else checks out

Common fixes

  • Repair wiring and clean or replace connectors
  • Replace failed glow plugs
  • Replace the glow plug control module or relay
  • Correct ground or power problems and replace a weak battery
  • Replace or reprogram the ECM if all else is good

Questions and answers

What does P038E mean?

It means the ECM found a low signal or fault in glow plug heater circuit 'B' on a diesel engine. The circuit is not behaving the way the ECM expects.

Can I drive with P038E?

For a short time, especially in warm weather. Cold starts may become difficult and rough running adds stress to the engine, so don't put the repair off.

Where should I start diagnosing P038E?

Check the battery, grounds and connectors, then measure glow plug resistance. Most often the fault is in the wiring or the glow plugs themselves.

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.