Diagnostic Aids
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
If the glow plug relay is stuck in the ON position, check for proper operation of the glow plugs, refer to Glow Plug System Diagnosis . When glow plugs are commanded ON by the scan tool, an internal ECM timer protects the glow plugs from damage by cycling them ON for 3 seconds and then OFF for 12 seconds.
The glow plug output feed wire nut and battery feed wire nut at the relay should be checked for proper torque, 5 N.m (44 lb in) and for corrosion.
An intermittent may be caused by the following:
- Poor connections
- Rubbed through wire insulation
- Broken wire inside the insulation