SERVICE MANUAL UPDATE SEC.6D3 CHARGING SYSTEM DIAGNOSIS

Subject: CHARGING SYSTEM DIAGNOSIS

Model and Year: 1990-91 GEO STORM

Under certain conditions the Charge Indicator Lamps on 1990 and 1991 GEO Storms may remain lit after removing the generator during charging system diagnosis. Due to this condition, charging system diagnosis procedures found on pages 6D3-2 and 6D3-3 of the 1990 and 1991 GEO Storm Service Manuals (ST371-90 and ST371-91) should be replaced by the contents of this bulletin.

Trouble in the charging system will show up as one or more of the following conditions:

A. Faulty charge indicator lamp operation.

B. An undercharged battery, as evidenced by slow cranking or dark hydrometer.

C. An overcharged battery, as evidence of spewing of electrolyte from the vents.

To diagnose the charging system, use the following procedure:

1. Visually check belt and wiring.

2. Turn ignition switch to "ON". If charge indicator lamp lights, proceed to Step 3. If lamp does not light, perform the following procedure:

a. Disconnect generator connector.

b. Connect a J 36169 fused jumper from generator terminal. L to chassis ground.

If charge indicator lamp lights, replace generator.

If charge indicator lamp does not light, repair open circuit in WHT/BLU, YEL or BLK/RED wire between generator and ignition switch.

3. Start and run engine at moderate speed. If charge indicator lamp does not light, proceed to Step 4. If lamp lights, perform the following procedure:

a. Turn ignition switch to "OFF".

b. Disconnect generator connector.

c. Remove heater and A/C relay from fuse and relay box.

d. Disconnect shift lock control module connector (automatic transaxle equipped vehicles).

e. Turn ignition switch to "ON".

If charge indicator lamp lights, repair short to ground in WHT/BLU wire between instrument panel cluster, heater and A/C relay, shift lock control module (automatic transaxle equipped vehicles) and generator.

If charge indicator lamp does not light, connect a J 34029-A digital multimeter from generator connector terminal L to chassis ground and measure voltage.

If reading is more than 10.0 volts, replace generator.

If reading is less than 10.0 volts, repair open circuit in WHT/BLU wire between generator and instrument panel cluster.

f. Reconnect shift lock control module connector (automatic transaxle equipped vehicles). If charge indicator lamp does not light, proceed to Step 4. If lamp lights, replace shift lock control module.

4. Battery undercharged or overcharged.

a. Disconnect generator connector.

b. Connect a J 34029-A digital multimeter from generator connector terminal L to chassis ground. Turn ignition switch to "ON" and measure voltage.

If reading is more than 10.0 volts, proceed to Step c.

If reading is less than 10.0 volts, repair open circuit in WHT/BLU wire between generator connector terminal L and battery.

c. Reconnect generator connector.

d. With all accessories turned off, connect a J 34029-A digital multimeter across the battery terminals. Run the engine at a moderate speed and measure voltage.

If reading is less than 16.0 volts, proceed to Step e.

If reading is more than 16.0 volts, replace the generator.

e. Connect a J 34029-A digital multimeter to generator output terminal. Turn on all accessories and load battery with carbon pile to obtain maximum amperage. Maintain voltage at 13.0 volts or higher. Measure amperage with an ammeter.

If generator output is less than 60 amps, replace generator.

If generator output is more than 60 amps, refer to BATTERY (Section 6D1) for Battery Load Test.

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.