SERVICE MANUAL UPDATE SEC.8A ELECT. INSTRUMENT PANEL

SUBJECT: SERVICE MANUAL UPDATE - 8A-ELECTRICAL (DIAGNOSIS PROCEDURES) INSTRUMENT PANEL INDICATORS CLUSTER U2E

VEHICLES AFFECTED: 1991 NINETY-EIGHT

The following charts contain revised diagnosis procedures for INSTRUMENT PANEL: INDICATORS CLUSTER, U2E, Section 8A, Cell 80 of the 1991 Ninety-eight Service Manual.

SYSTEM CHECK TABLE

SYMPTOM FOR DIAGNOSIS ------------------------------- --------------------------------------- Both Speedometer and Odometer See Section 8A-33 do not operate properly

Either Speedometer or Odometer Replace Instrument Cluster (see does not operate Section 8C)

Instrument Panel Illumination See Interior Lights Dimming, Lights do not operate Section 8A-117

Fuel Gage always indicates E Do Test B (also see Test A, terminals B6 and B7)

Fuel Gage always indicates F Do Test C (also see Test A, terminals B6 and B7)

Fuel Gage is not accurate Do Test D (also see Test A, terminals B6 and B7)

Coolant Temperature Gage Do Test H (also see Test A, terminal always reads cold B13)

Coolant Temperature Gage Do Test G (also see Test A, terminal always reads hot B13)

Coolant Temperature Gage Do Test I (also see Test A, terminal is not accurate B13)

AMP Indicator does not See Starter And Charging System, operate properly Section 8A-30

ANTILOCK Indicator does See Antilock Brake System, Section not operate properly 8A-44

OIL Indicator is always lit Do Test E (also see Test A, terminal A9) OIL Indicator does not light Do Test F (also see Test A, terminal with Ignition Switch in A9) RUN (engine not running)

HOT Indicator does not See Section 6E3 operate properly

FIRM RIDE Indicator does See Section 3G not operate properly

BRAKE Indicator does not See Brake Warning System, Section operate properly 8A-41 (also do Test A, terminal A1)

SERVICE ENGINE SOON Indicator See Section 6E does not operate properly

Hi Beam Indicator does See Section 8A-100 or 8A-101 (also not operate properly see Test A, terminal A17)

Turn Indicators do See Exterior Lights, Section 8A-110 not operate properly (also see Test A, terminals A2 and A8)

FASTEN BELTS Indicator See Warnings And Alarms: Chime, Section does not operate properly 8A-76 (also see Test A, terminal A4)

LOW FUEL Indicator does not See Warnings And Alarms: Reminder operate properly Package, Section 8A-77

LOW WASH FLUID Indicator See Warnings And Alarms: Reminder does not operate properly Package, Section 8A-77

B: FUEL GAGE ALWAYS INDICATES E --------------------------------- Disconnect Fuel Tank Unit connector C409. Tum Ignition Switch to RUN and observe the Fuel Gage.

o If the Fuel Gage now indicates F, replace the Fuel Gage Sender.

o If the Fuel Gage still indicates E, check connections and the PPL (30) wire for a short to ground (see schematic). If the wire is good, replace the Instrument Cluster (see Section 8C).

C: FUEL GAGE ALWAYS INDICATES F --------------------------------- Disconnect Fuel Tank Unit connector C409 and jumper harness half of terminal B (PPL) to ground. Tum Ignition Switch to RUN and observe the Fuel Gage.

o If the Fuel Gage now indicates E, check BLK/WHT (803) wires for an open (see schematic). If wires and ground are OK, replace the Fuel Gage Sender.

o If the Fuel Gage still indicates F, check the PPL (30) wire for an open (see schematic). If OK. replace the Instrument Cluster (see Section 8C).

D: FUEL GAGE ACCURACY TEST ---------------------------- Disconnect Fuel Tank Unit connector C409 and connect the two red clip leads of tester J 33431 to terminals B (PPL) and D (BLK/WHT) of the harness half of that connector. With the Ignition Switch in RUN, set the resistance dial on the tester to 0 ohms (E), 44 ohms (1/2), and 90 ohms (F).

o If the Fuel Gage responds correctly, install a new Fuel Gage Sender.

o If the Fuel Gage does not respond correctly, check PPL (30) and BLK/WHT (803) wires for high resistance. Also check the Instrument Cluster screws at the back of the cluster. They should be clean and tight. If all checks are OK, replace the Instrument Cluster (see Section 8C).

E: OIL PRESSURE INDICATOR IS ALWAYS LIT ----------------------------------------- 1. Check oil level and pressure with a mechanical gage.

o If oil level and pressure are OK, go to step 2.

o If oil level and pressure are not OK, see Section 6 of the Service Manual.

2. With Ignition Switch in RUN, disconnect the Oil Pressure Switch connector.

o If the OIL Pressure Indicator is now out, replace the Oil Pressure Switch.

0 If the OIL Pressure Indicator is still lit, check the TAN (31) wire and the Multi-Function Chime Module (Y67) for a short to ground (see schematic). If wire is OK, replace the Instrument Cluster (see Section 8C).

F: OIL PRESSURE INDICATOR DOES NOT LIGHT WITH THE IGNITION SWITCH IN RUN (ENGINE NOT RUNNING) -------------------------------------------------------------------------- Connect: FUSED JUMPER At: OIL PRESSURE SWITCH CONNECTOR (Disconnected) Condition: Ignition Switch; RUN

Jumper Correct For Between Result Diagnosis ---------------- ----------- --------- A (TAN) & Ground OIL Pressure (see schematic) Indicator lights See 1

A (TAN) & B (BLK) OIL Pressure See 2 Indicator lights

o If the OIL Pressure Indicator lights, replace the Oil Pressure Switch.

1. Check/repair TAN (3 1) wire for an open. If wire is OK, replace the Instrument Cluster (see Section 8C).

2. Check/repair BLK (154) wire for an open or high resistance.

G: COOLANT TEMPERATURE GAGE ALWAYS READS HOT -------------------------------------------- Disconnect the Coolant Temperature Sender terminal and turn the Ignition Switch to RUN.

o If the Coolant Temperature Gage indicates C, replace the Coolant Temperature Sender.

o If the Coolant Temperature Gage does not indicate C, check the DK GRN/WHT (635) and VMT/BLK (235) wires for a short to ground (see schematic). If wires are OK, replace the Instrument Cluster (see Section 8C).

H: COOLANT TEMPERATURE GAGE ALWAYS READS COLD ---------------------------------------------- Disconnect the Coolant Temperature Sender terminal. Jumper the DK GRN/WHT (635) wire to ground and tum the Ignition Switch to RUN.

o If the Coolant Temperature Gage indicates H, replace the Coolant Temperature Sender.

o If the Coolant Temperature Gage still indicates C, check the DK GRN/WHT (635) and WHT/BLK (235) wires for an open. If OK, replace the Instrument Cluster (see Section 8C).

1: COOLANT TEMPERATURE GAGE ACCURACY TEST ------------------------------------------ Disconnect the Coolant Temperature Sender terminal. Connect one red clip lead of the J 33431 tester to the harness terminal DK GRN/WHT (635) wire, and the other red clip lead to ground. Adjust the resistance dials of the tester to 1365 ohms, 93 ohms and then to 55 ohms. The Coolant Temperature Gage should indicate C. midscale, and then H.

o If the Gage indicates correctly, the wiring and Gage are good. Replace the Coolant Temperature Sender.

o If the Gage does not indicate correctly, check the DK GRN/WHT (635) wires and WHT/ BLK (235) wires for high resistance. If they are OK, replace the Instrument Cluster (see Section 8C).

J: LOW COOLANT INDICATOR TEST ------------------------------ Measure: VOLTAGE At: LOW COOLANT MODULE CONNECTOR (Disconnected) Condition: o Ignition Switch: Run

Measure Correct For Between Voltage Diagnosis --------------------- ------- ---------- C (PNK/BLK) & Ground Battery See 1

C (PNK/BLK) & A (BLK) Battery See 2

B (YEL/BLK) & Ground Battery See 3

o If all voltages are correct, replace the Low Coolant Module.

1. Check I/P Fuse Block Fuse 20 and PNK/BLK (I 176) wire for an open. 2. Check BLK (155) wire for an open. 3. Check YEL/BLK (68) wire and bulb for an open or short to ground.

K: CHECK OIL INDICATOR DOES NOT LIGHT ------------------------------------- Measure: VOLTAGE At: OIL LEVEL MODULE CONNECTOR (Disconnected) Condition: o Ignition Switch: Run

Measure Correct For Between Voltage Diagnosis -------------------- -------- --------- 10 (ORN) & Ground Battery See 1

9 (PNK/BLK) & Ground Battery See 2

6 (BRN/WHT) & Ground Battery See 3

6 (BRN/WHT) & 5 (BLK) Battery See 4

o If all results are correct, replace the Oil Level Module.

1. Check I/P Fuse Block Fuse II and ORN (40) wire for an open.

2. Check I/P Fuse Block Fuse 20 and PNK/BLK (1176) wire for an open.

3. Check BRN/WHT (1173) wire and bulb for an open.

4. Check BLK (154) wire for an open.

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. One circuit 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 larger 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 resistance is high. More current now flows through the F coil, which moves the pointer towards F on the scale.

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

COOLANT TEMPERATURE GAGE

Two coils also operate the Coolant Temperature Gage. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender. The Coolant Temperature Sender has 55 ohms resistance at 260 deg. F (127 C) and its resistance becomes greater at lower temperatures. I has approximately 1400 ohms at 100 F (38 C). This varying resistance causes the current through the Sender and one coil to change as the coolant temperature changes. This moves the pointer.

SPEEDOMETER AND ODOMETER

The speedometer is operated by and electronic circuit. The Vehicle Speed Sensor (VSS), located in the Transaxle, generates an AC voltage with a frequency proportional to the speed of the vehicle. This goes to the Powertrain Control Module (PCM) and then to the Speedometer circuit board in the Instrument Cluster. The Solid State unit drives the pointer of the Speedometer.

The same buffered speed signal from the PCM is processed to drive the Odometers. The Odometers are operated by a stepper motor that responds to pulses from the Speedometer circuit.

HOT INDICATOR

The HOT Indicator lights to warn of overheating when the Coolant Temperature Sender Switch is closed. The PCM controls this indicator. When the PCM senses an over-temperature condition, it grounds the HOT indicator. When the Ignition Switch is in RUN with the engine off, the HOT indicator is grounded by the PCM as a bulb test.

LOW COOLANT INDICATOR

The LOW COOLANT Indicator is controlled by the LOW COOLANT Module, which receives power when the Ignition Switch is in RUN. When the coolant level is low, the Low Coolant Module grounds the indicator circuit.

CHECK OIL INDICATOR

The CHECK OIL Indicator lights to alert the driver of a low engine oil level condition. The low oil sensing circuit consists of a Low Oil Level Sensor and and Oil Level Module. This system is active only at initial engine starting and not while the engine is running.

The oil level will be measured if the engine has been off long enough for top engine oil to have returned to the pan and if the vehicle is on a fairly level surface. The Oil Level Module receives battery power at all times to retain memory of engine on and off times.

When the Ignition Switch is turned to RUN, battery voltage is applied to the ignition on input of the Oil Level Module, and the Oil Level Module grounds the CHECK OIL Indicator for 2 seconds as a bulb check. If the ignition on input has been at 0 volts for at least 8 minutes and the internal attitude sensor indicates that the vehicle is resting on a surface with an incline of 20 degrees of less, the Oil Level Module activates the Low Oil Level Sensor. If the sensor returns a signal indicating a good oil level signal, in indicator will remain off. If the sensor returns a signal indicating a low oil condition, the indicator is lit 15 to 20 seconds after the bulb check. If the ignition switch is turned off for less than 20 seconds, the Oil Level Module will remember and display the previous oil level status and ignore the present oil status. If the ignition has been off for more than 20 minutes, but less than 8 minutes, the Oil Level Module will ignore the Low Oil Level Sensor and perform a bulb check only.

OIL PRESSURE INDICATOR

The Oil Pressure Indicator goes on to warn of low oil pressure when the Oil Pressure Switch is closed. The Oil Pressure Switch closes when the oil pressure falls below 27 kPa (4psi). When the engine is initially cranked, oil pressure is below 27 kPa, so the Oil Pressure Switch closes, and the OIL Pressure Indicator goes on momentarily as a bulb test. The Oil Pressure Switch opens as soon as the oil pressure is above 27 kPa (4psi), and the OIL Pressure indicator goes off.

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.