Diagnostic Aids

If glow plug relay was stuck in ON position, check for proper operation of glow plugs. When glow plugs are commanded on by scan tester, an internal PCM timer protects glow plug from damage by cycling them on for 3 seconds and then off for 12 seconds.

Fig 1: DTC 29 Schematic ("G" Series) Glow Plug Relay Circuit Fault

Fig 2: DTC 29 Schematic ("P" Series) Glow Plug Relay Circuit Fault

Fig 3: DTC 29 Flow Chart (All Models) Glow Plug Relay Circuit Fault