Glow Plug/Heater Indicator Circuit Malfunction
The glow plug heater indicator circuit has detected a malfunction in the glow plug system, which is critical for diesel engine starting. This code indicates the vehicle's computer cannot properly control or monitor the glow plugs, preventing them from pre-heating the combustion chambers before starting.
What You Might Notice
- Delayed engine startup, especially in cold weather
- Excessive white or gray smoke from the exhaust
- Glow plug indicator light not illuminating on the dashboard
- Engine may not start at all in very cold conditions
- Rough idle after a cold start
Most Common Causes
- 1
Faulty Glow Plug Relay
The relay controlling power to the glow plugs may be stuck open, burnt out, or electrically faulty. This prevents voltage from reaching the glow plugs during the pre-heat cycle.
- 2
Broken or Failed Glow Plugs
One or more glow plugs may be burned out, corroded, or disconnected. A single failed glow plug can trigger this code on some vehicles.
- 3
Wiring or Connector Issues
Corroded connections, damaged wiring harnesses, or loose connectors in the glow plug circuit can interrupt the signal between the engine control module and the glow plugs.
- 4
Engine Control Module Malfunction
The ECM itself may have failed or experienced a software corruption preventing it from properly controlling the glow plug circuit.
How to Diagnose It
- 1
Check Faulty Glow Plug Relay — The relay controlling power to the glow plugs may be stuck open, burnt out, or electrically faulty. This prevents voltage from reaching the glow plugs during the pre-heat cycle.
- 2
Check Broken or Failed Glow Plugs — One or more glow plugs may be burned out, corroded, or disconnected. A single failed glow plug can trigger this code on some vehicles.
- 3
Check Wiring or Connector Issues — Corroded connections, damaged wiring harnesses, or loose connectors in the glow plug circuit can interrupt the signal between the engine control module and the glow plugs.
- 4
Check Engine Control Module Malfunction — The ECM itself may have failed or experienced a software corruption preventing it from properly controlling the glow plug circuit.
How to Fix It
- 1
Inspect and Test Glow Plug Relay
Locate the glow plug relay in the fuse/relay box and test it with a multimeter for continuity and proper switching. Replace the relay if it fails testing or shows signs of burn marks.
- 2
Check and Replace Glow Plugs
Remove each glow plug and test with a multimeter or dedicated glow plug tester. Replace any plugs that do not show proper resistance or fail the heating test.
- 3
Inspect Wiring and Connectors
Visually inspect the glow plug harness and connectors for corrosion, burns, or loose connections. Clean corroded connectors with electrical contact cleaner or replace damaged wiring sections.
- 4
Verify Engine Control Module
After checking other components, have the ECM scanned for internal faults or reprogrammed if necessary. In rare cases, the module may need replacement.
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