SERVICE MANUAL UPDATE SEC. 8A GAUGE CLUSTER DIAG. REVISED
SUBJECT: SERVICE MANUAL UPDATE - REVISED ON-BOARD DIAGNOSTIC PROCEDURES, GAGE CLUSTER (UB7) AND DIGITAL CLUSTER (U2A), CORRECT PAGE LOCATION 8A-81-27
MODELS/YEARS: 1991 NINETY-EIGHT
The 1991 Ninety-Eight Service Manual at Page 8A-81-17, INSTRUMENT PANEL; GAGES CLUSTER, UB7 and Page 8A-82-16, INSTRUMENT PANEL; DIGITAL CLUSTER, U2A - DIC ON-BOARD DIAGNOSTICS has been revised with the following procedure:
DRIVER INFORMATION CENTER (DIC) ON-BOARD DIAGNOSTICS
o The following procedure must be performed before the Driver information On-Board Diagnostics can be used. To enter the diagnostic mode, do the following:
1. With the Ignition Switch in Run, press the DEST key 2. Press RESET 3. Press 8192 (ETA, ECON, E/T, FUEL) 4. Press ENTER.
The Driver Information Center will now be in the diagnostic mode.
o Display position FF was not included in the Driver information Reference Diagram, please add the following:
POSITION FF - Oil pressure, 0 to 99% of maximum pressure
PAGE CORRECTION: 8A-81-27 --------------------------- In the 1991 Ninety-Eight Service Manual, Electrical Diagnosis, Section 8A, Page 81-27, was printed incorrectly. Use the following INSTRUMENT CLUSTER: GAGES CLUSTER, UB7, Page BA-81-27.
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.
