Circuit/System Testing

IMPORTANT: If a glow plug control circuit is shorted to 12 volts, the glow plug will be damaged and the glow plug must be replaced.

IMPORTANT: If a glow plug is replaced and the tip is missing or burned off, the cylinder head must be removed and all debris be cleaned out of the cylinder.

With the ignition ON and the glow plugs not commanded ON, probe the affected glow plug with a test lamp connected to a ground. Observe that the test lamp does not illuminate.
- If the test lamp does illuminate, test the glow plug control circuit for a short to voltage or for a faulty glow plug control module (GPCM).
With the ignition ON, probe the affected glow plug with an unpowered test lamp connected to ground. Command the glow plugs ON with a scan tool and observe the test lamp.
- If the test lamp does not illuminate, test the affected glow plug harness between the glow plug control module and the glow plug for an open, short to ground or high resistance.
With the ignition OFF and the affected glow plug disconnected, measure the resistance between the affected glow plug terminal and ground with a DMM for less than 1 ohm.
- If the resistance is more than 1 ohm, test the affected glow plug control circuit for a short to voltage and replace the damaged glow plug.
With the ignition OFF and the glow plug control module harness disconnected, measure the resistance between the affected glow plug harness connector and the glow plug control module harness connector for less than 1 ohm resistance.
- If the resistance is more than 1 ohm, repair the harness.
- If the resistance is less than 1 ohm, replace the glow plug control module.