DIESEL ENGINE GLOW PLUG DIAGNOSIS FOR WAIT LIGHT

The glow plug system used on 1981-83 Grand Prix/Bonneville contains an electronic module with diagnostic features. In the event of a system failure, the wait light may stay on or come back on after the engine is started. The system is also very dependent on a good ground to operate properly. By a good ground it is meant that it is a zero resistance connection confirmed by the use of a digital volt ohm meter on the 200 scale. Do not over look the resistance in the meter leads when performing these checks. If it does not get a zero resistance ground, the performance may suffer.

Lack of zero resistance ground accounts for the greatest number of problems in this system.

There are four grounds to be concerned with. First check the battery to engine, the engine to the cowl, (braided strap at the rear of engine) the ground behind the left hand valve cover (G181) and behind the instrument panel to the left of the steering column (G104).

Conditions have been encountered with the glow plugs coming on one time and quickly going off after a Goodwrench engine has been installed.

We are finding that the braided ground strap at the rear of the engine has not been reconnected.

The following conditions can cause the wait light to come back on or stay on:

1. Glow plug burned out.

2. No continuity in blue and black wires at the glow plug relay and terminal E at the module.

3. No continuity in purple or gray wire between sensor and module.

4. Bad diode trio in generator.

5. No continuity in brown wire between generator and module.

6. High resistance in blue wire at the glow plug relay and terminal E at the module, or high resistance in the black wire at the glow plug relay and the orange wire with black tracer at the control sensor.

7. Loose glow plug terminals.

8. Poor grounds.

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.