Possible Causes

Insufficient glow plug ON time will not allow enough heat to accumulate in the combustion chamber to easily facilitate starting. If the glow plug system ON time does not meet any of the specifications in the accompanying chart the problem is most likely a faulty wire harness connection, ground connections or GPCM. Look very carefully for poor connections or loose fitting pins that will cause high resistance.

• Powering circuit to glow plug relay (fusible links from starter relay).
• Glow plugs.
• Defective glow plug BUSS bar.
• Defective Glow Plug Control Module (GPCM).
• Engine wiring harness.