GLOW PLUGS FAIL TO HEAT SHORTED ALTERNATOR POS. DIODE

VEHICLES AFFECTED: 1982-83 C/K/G/P Trucks With 6.2L Diesel

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 No. 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.

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 three 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 three volts) will be present in the brown wire. This is normal.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.