Powertrain Controls - ECM/PCM

DTC 29 Glow Plug Relay Circuit Fault:

Glow Plug Relay Circuit Fault:

CIRCUIT DESCRIPTION
The glow plug system is used to assist in providing the heat required to begin combustion during engine starting at cold ambient temperatures. The glow plugs are heated before and during cranking, as well as initial engine operation. The Powertrain Control Module (PCM) controls the glow plugs by sending a B+ signal.

DIAGNOSTIC TROUBLE CODE (DTC) 29 WILL SET WHEN
^ low plugs commanded "ON" and "glow plug volts" is less than 0.8 volt.
OR
^ Glow plugs "OFF" and "glow plug volts" is greater that 0.8 volt.
OR
^ "System voltage" exceeds "glow plug volts" by 2 volts.

ACTION TAKEN (PCM will default to)
Hard start.

DTC 29 WILL SET WHEN
The fault condition(s) no longer exist.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step will determine if DTC 29 is a hard failure.
2. The Tech 1 scan tool may not display system voltage. The important thing is that the PCM is cycling voltage "ON" and "OFF" indicating that the PCM is OK.
3. This step will check relay feed circuit.
4. This step will check relay ground.
5. This step will determine if CKT 505 is open.
6. This step will check relay and wiring.

DIAGNOSTIC AIDS
If glow plug relay was stuck in the "ON" position, check for proper operation of glow plugs. When glow plugs are commanded "ON" by the Tech 1, an internal PCM timer protects the glow plugs from damage by cycling them "ON" for 3 seconds and the "OFF" for 12 seconds. Refer to Glow Plug. Testing and Inspection