SERVICE MANUAL UPDATE-SEC.8A REVISED ELEC. DIAGNOSIS CHART

Model and Year: 1991 B CAR

The following pages update Section 8A Electrical Diagnosis of the 1991 B car Service Manual: 8A-87-4 and 8A-87-7.

CIRCUIT OPERATION LOW COOLANT INDICATOR

The Low Coolant Indicator has its ground controlled through the Low Coolant Module. The module uses the varying resistance in the Low Coolant Probe to determine if a low coolant condition is present. If a low coolant condition is present, the module will ground CKT 69, turning "ON" the indicator.

LOW FUEL INDICATOR

The Low Fuel Indicator has a permanent ground to CKT 150, with its voltage being controlled from the Low Fuel Module within the Fluid Warning Center. When the module senses a resistance in the Fuel Tank Unit that represents approximately 1/8 tank of fuel, the module turns "ON" the indicator. Refer to "Instrument Panel: Indicators Cluster," page 8A-80-11 for an approximate sender resistance chart.

LOW OIL INDICATOR

The Low Oil Indicator ground is controlled by the Low Oil Module. To check for a low oil condition, the Low Oil Module looks for a ground through the Oil Level Switch after the Ignition Switch has been turned to "OFF" or "LOCK."

The Low Oil Module checks for a low oil condition 32 minutes after the Ignition Switch is turned to "OFF" or "LOCK," if the previous ignition cycle was less than 12 minutes. If the previous ignition cycle was longer than 12 minutes, the Low Oil Module checks for a low oil condition 3 minutes after the Ignition Switch is turned to "OFF" or "LOCK."

When the Low Oil Module loses the ground through the Oil Level Switch (Oil Level Switch open indicating low oil level) the Low Oil Module grounds the low Oil Indicator for the duration of the next ignition cycle.

When the Low Oil Module is grounded through the Oil Level Switch, the Low Oil Module grounds the Low Oil Indicator for a bulb test when the Ignition Switch is turned to "RUN" during the next ignition cycle. The bulb test takes four to five seconds.

LOW SOLVENT INDICATOR

The Windshield Washer Solvent Tank has a Washer Fluid Level Switch which closes when the washer solvent level becomes low. At this time, voltage is applied to the Low Solvent Indicator. With the indicator ground permanent to CKT 150, the indicator will be turned "ON."

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.