10 - Glow Plug System Operation

Purpose:
To determine if the glow plug system operation is sufficient to permit starting.

On California only, the glow plug system monitor will start when the glow plugs are commanded on for more than 35 seconds and the battery voltage is between 11.8-14 volts. A glow plug code will be stored in Continuous memory if one or more glow plugs are not being powered.

NOTE: Look very carefully for poor connections, burnt looking or loose fitting pins that will cause high resistance and set a code.

The Glow Plug Monitor Self Test is a functional test of the PCM performed on demand with the engine running and the A/C off. This test will activate the glow plug relay and detect any difference in the amount of current between both banks. Battery voltage must be 11.8-14 volts to complete the test. It may be necessary to raise engine rpm to maintain battery voltage. A fault must be present at the time of testing for the KOER Glow Plug Monitor Self Test to detect a fault. If a fault is detected, a DTC will be the output on the data link at the end of the test when requested by a scan tool. Only a hard fault code (DTC) will be displayed.

You can verify glow plug ON time (and amps for California) by monitoring NGS PIDs EOT and GPCTM (California GPMR and GPML). The wait to start lamp ON time (1-10 seconds) is independent from glow plug relay ON time.

Recommended Procedure:
Install a digital multimeter on the glow plug feed side of the glow plug relay (large stud with two wires connected). Turn the ignition key to the ON position but do not attempt to start. Note the time in seconds from when the key is turned ON and the glow plug relay energizes until the glow plug relay de-energizes. Glow plug ON time is dependent on oil temperature and altitude. The glow plug relay comes ON between 1-120 seconds and does not come ON at all if EOT is above 30 °C (860° F) for 49-state or 55°C (131 °F) for California. The wait to start light is independent from glow plug relay ON time. The glow plug relay makes a loud click noise which is easily heard when it energizes and de-energizes. The dome light will dim and the dash voltmeter will dip when the glow plugs are drawing current from the battery. Compare the times measured to the table (time will be affected by engine temperature, battery condition and vehicle altitude). The voltage at the glow plug feed terminal may vary from 9 to 12 volts depending upon battery condition.

If battery voltage is not present, check for B+ at the power supply terminal (terminal with single large wire). Power for glow plug power supply is supplied from the starter relay through two fusible links at solenoid.

Disconnect all of the glow plug/injector harness connectors from the valve cover gaskets. With the Glow Plug Injector Adapter 014-00935 or equivalent installed, measure glow plug resistance to ground (preferably B-). A resistance measurement of 0.1-2 ohms indicates a good glow plug.

Glow plug Harness Continuity
Measure for continuity from the connector harness to the glow plug feed terminal on the glow plug relay. Resistance should be less than 0.1-1 ohm.

Incorrect measurements will result if all glow plug/injector connectors to valve cover are not disconnected.

Possible Causes:
Insufficient glow plug ON time will not allow enough heat to accumulate in the combustion chamber to easily facilitate starting. If the glow plug system ON time does not meet any of the specifications in the accompanying chart the problem is most likely a faulty wire harness connection, ground connections or glow plug relay.

NOTE: Look very carefully for poor connections, burnt looking or loose fitting pins that will cause high resistance.

- Glow plug relay.
- Powering circuit to glow plug relay (fusible links from starter relay).
- Glow plug relay to valve cover connector circuits.
- Valve cover gasket.
- Under Valve Cover (UVC) harness.
- Glow plugs.

Tools Required:
- 23 Multimeter 105-00050 or equivalent
- Glow Plug Injection Adapter 014-00935 or equivalent
- Stopwatch or equivalent