For 1990-2009 cars

# SERVICE MANUAL UPDATE SEC. 8A GAUGE CLUSTER DIAG. REVISED

#### SUBJECT: SERVICE MANUAL UPDATE - SECTION 8A-ELECTRICAL-INSTRUMENT CLUSTER, GUAGES CLUSTER, UB7 - (CORRECT PAGE LOCATION)

#### MODELS/YEARS: 1991 "C"

In the Service Manual, Electical Diagnosis, Section 8A, Page 81-27, was printed incorrectly. Replace with the following INSTRUMENT CLUSTER: GUAGES CLUSTER, UB7, Page 8A-81-27.

(Continued from previous page)

C1/B12 & Less than 2 ohms See 1 C2/B8 C1/B12 & Open Load See 1 C2/B7

#### o ENTER button held

C1/B12 & Less than 2 ohms See 1 C2/B7 C1/B13 & Open Load See 1 C2/B9

#### o SPEED (4) button held

C1/B13 & Less than 2 ohms See 7 C2/B9 C1/B13 & Open Load See 1 C2/B8

#### o ETA (8) button held

C1/B13 & Less than 2 ohma See 1 C2/B8 C1/B13 & Open Load See 1 C2/B7

#### o RESET button held

C1/B13 & Less than 2 ohms See 1 C2/B7

o If all resistances are correct, check the 1481,1482,1483,1484,1485,1486,and 1487 wires for a short to ground (see schematic). If OK, replace the Instrument Cluster (see Section 8C).

1. Replace the DIC Switch Assembly (see Section 8C).

2. Check the DK BLU (1481) and TAN (1487) wires for an open. If OK, replace the DIC Switch Assembly (see Section 8C).

3. Check the ORN (1486) wire for an open. If OK, replace the DIC Switch Assembly (see Section 8C).

4. Check the RED (1485) wire for an open. If OK, replace the DIC Switch Assembly (see Section 8C).

5. Check the LT BLU (1482) wire for an open. If OK, replace the DIC Switch Assembly (see Section 8C).

6. Check the DK GRN (1483) wire for an open. If OK, replace the DIC Switch Assembly (see Section 8C).

7. Check the LT GRN (1484) wire for an open. If OK, replace the DIC Switch Assembly (see Section 8C)

#### CIRCUIT OPERATION

The operation of an individual Indicator is described along with its circuit. Refer to the schematic and text for the circuits described below.

#### Fuel Gage

The magnetic fields of two coils, which are at right angles to each other, move the pointer of the Fuel Gage. Battery voltage is applied to the E coil, and the circuit divides at the opposite end of the coil. Another goes to ground through the F coil. Another goes to ground through the variable resistor of the Fuel Gage Sender.

When the tank is low, the resistance of the Sender is low. A large flow of current passes through the E coil and the Fuel Gage Sender resistor to move the pointer towards E on the scale. When the tank is full, the Sender resis- tance is high. More current now flows through the F coil, which moves the pointer toward F on the scale.

With two coils operating the pointer, the Gage is not affected by changes in the vehicle's electrical system.

#### Oil Pressure Gage

The engine off pressure is displayed by the Oil Pressure Gage. The pointer of the Gage is moved by two coils, and its operation is similar to that of the Fuel Gage.

The Oil Pressure Sender/Switch is connected to the junction of the two coils. It has low resistance when the oil pressure is low, and 90 ohms resistance when the oil pressure is high. This changing resistance changes the current flow through the coils. The magnetic fields of the coils move the pointer from low to high.

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.