PISTON 3872966 - Caterpillar

Operation Description:The ECM monitors the primary contacts of the glow plug relays and will activate a diagnostic if there is a problem with them. The ECM does not monitor the secondary side of the relay. If there is a problem with the secondary contacts on the relay or if there is a problem with the glow plug, no diagnostic code will be recorded. If a glow plug does not heat up, the burner will not ignite successfully.Perform the following procedure when the glow plug is not functioning correctly and there is no diagnostic code active for the affected glow plug relay.Test Step 1. Check Glow Plug
Turn the key start switch to the ON position.
Turn the burner system switch to the BURNER position and move all the burner mode switches to the OFF position.
Turn the burner mode switch for the suspect burner to the MANUAL position.
Wait 30 seconds. At the glow plug relay, measure the voltage between relay contact 87 (glow plug load side) and frame ground.Expected Result:The DCV should measure between 21 DCV and 29 DCV.Results:
OK - The voltage measurement is between 21 DCV and 29 DCV.Repair: The relay is working correctly. If the glow plug is not getting hot, either the wiring between the relay and the glow plug is not correct or the glow plug is malfunctioning. Ensure that the ground connection for the glow plug is clean and intact. Repair the wiring harness or replace the glow plug. Stop.
NOT OK - The voltage measurement is less than 21 DCV.Repair: Either the relay or the machine harness wiring is not correct. Proceed to Step 2.Test Step 2. Check Glow Plug Relay
The first three Steps in Test Step 1 remain in effect.
Wait 30 seconds. At the glow plug relay, measure the voltage between relay contact 30 (supply side wire P118-GY) and frame ground.Expected Result:The DCV should measure between 21 DCV and 29 DCV.Results:
OK - The voltage measurement is between 21 DCV and 29 DCV.Repair: The wiring is correct. The relay is malfunctioning. Replace the glow plug relay. Stop.
NOT OK - The voltage measurement is less than 21 DCV.Repair: There is a problem with the + battery supply on wire P118-GY. This wire also supplies + battery power to the ECM. The problem is in the machine harness. Ensure that the wire P118-GY is intact and is not open or shorted. Repair or replace the machine harness. Stop.