The glow plug relay is located at the rear of the left cylinder head. When commanded by the PCM, the relay contacts close, allowing ignition voltage to reach the two sets of glow plugs. The PCM uses a B+ signal to control the solid state circuitry of the glow plug relay. The glow plug lamp in the instrument cluster alerts the driver to faults in the glow plug system.
Glow Plug Circuit Operation
The PCM energizes the glow plug relay on CKT 505 (figure 5-42). When energized, the relay transfers battery power, which it receives on CKT 2, to the left glow plugs on CKT 503 and the right glow plugs on CKT 509. The PCM receives glow plug signal feedback on CKT 507. The PCM uses voltage on CKT 507 to illuminate the “Glow Plug” lamp when the glow plugs are “ON.” Ground for the glow plug relay is provided on CKT 150.
DTC 29 — “Glow Plug System Fault”
DTC 29 sets under any of the following conditions.
1. When voltage on the glow plug feedback circuit to the PCM (CKT 507) differs from ignition voltage by 2 volts or more
2. When feedback voltage is less than .8 volts when the glow plugs are commanded “ON”
3. When feedback voltage is greater than .8 volts when the glow plugs are commanded “OFF”
The cause of a DTC 29 could be an open or short in CKT 39 or CKT 150, a faulty fuse, or a faulty connection.
