GLOW PLUG RELAY AND LAMP
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.
GLOW PLUG CURRENT TEST
Primary Checks
1. Install an ammeter at the controller/relay terminal stud (glow plug side).
2. Connect the Tech 1. Using the Tech 1’s “Glow Plug Output Tests,” command the glow plugs “ON.”
3. Move the ignition switch to the RUN position and measure the amperage of each bank of the glow plugs.
• If both banks have a minimum of 55 amperes current flow, the system is working properly.
• If either bank has less than 55 amperes current flow, go to step 4.
• If both banks have a zero ampere current flow, perform the Secondary Checks as described in
the “6.5L V8 Turbo Diesel” coursebook (#16015.12-2).
4. Install an ammeter in series with one glow plug wire. Move the ignition switch to RUN and measure the amperage of the glow plug.
• If the glow plug has a current flow of 14 amperes, it is working properly.
• If the glow plug has a current flow less than 14 amperes, go to step 5.
5. Check the continuity of the glow plug wiring harness from the relay terminal stud to the glow plug terminal.
• If the wiring harness has continuity, go to step 6.
• If the wiring harness has no continuity, repair it and check system operation.
6. Replace the glow plug and follow steps 4 and 5 for other glow plugs. Use an AC-type 9G glow plug.
7. When all glow plugs have 14 amperes of current flow, end the diagnosis.