Glow Plug Circuit Electrical Check
With ignition on and coolant temperature below 150°F (65°C), the ECM turns on the cold advance relay to supply 12 volts to the glow plug controller and the cold advance solenoid. The controller, in turn, will cycle the glow plugs on and off for a pre-determined amount of time. After engine is cranked, the glow plugs will again cycle on and off.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Disconnecting the coolant temperature sensor sends a low temperature signal to the ECM. The ECM turns on the cold advance relay which sends 12 volts to terminal "D" of the glow plug controller. If test light comes on during this test, the cold advance circuit and ECM are okay.
- If relay contacts are shorted together, there will be 12 volts supplied to the glow plugs at all times. Since glow plugs are 6 volt components, they will be damaged by the constant high voltage.
- This test checks for high resistance in the feedback circuit to the glow plug controller. High resistance in this circuit will signal the glow plug controller to turn off.
- This test determines if the glow plug controller is cycling its internal relay. Test light should cycle on and off if the glow plug controller is operating.
- This test checks for a complete circuit between the glow plug controller and each glow plug. If test light fails to come on, that glow plug feed circuit is open. It may be necessary to turn ignition off for 10 seconds and on again to keep the glow plug controller cycling.