Glow Plugs - No Start Condition, Fail to Heat

Number: 83-I-64

Section: VIy

Date: May, 1983
Subject: GLOW PLUGS FAIL TO HEAT - 1982-83 10-30 LIGHT DUTY "C-K-G-P" TRUCKS WITH 6.2L DIESEL


TO: ALL CHEVROLET DEALERS

A "no-start condition - due to no glow plug heating" can result from a shorted Delco alternator positive diode.

When this condition occurs in the alternator, battery voltage
can be supplied to the glow plug controller with the key in
the off position. This battery voltage is normally supplied
to pin #1 in the glow plug controller from the alternator
after the engine starts. This voltage, in effect, tells the
controller that the engine has started and shuts off the glow


plug heating cycle.


When a "no glow plug heating" condition is received, a quick check should be made to see if a shorted diode is the cause.

SKETCH 2 - WIRING HARNESS:

Procedure

1. Wait for a minimum of 15 minutes, or sufficient time for the controller to cool off.

2. With the key in the off position (engine stopped), check for battery voltage in the brown wire that goes from the alternator to the glow plug controller.

3. If a voltage is present, disconnect the brown wire from the alternator. Again, check for voltage in the brown wire. There should be none. (If the key is "ON", a low voltage - approximately 3 volts - will be present).

4. Turn the key on. If the glow plugs heat, the condition was with the alternator.

The only time battery voltage should be present in the brown wire is when the engine is running. With the key on, and the engine not running, a low voltage (approximately 3 volts) will be present in the brown wire. This is normal.