INSTRUMENT PANEL DIAGNOSIS MANUAL UPDATE

Model and Year: 1988 CELEBRITY SERVICE MANUAL UPDATE

The reverse side of this bulletin contains a replacement for page 8A-80-11 of the 1988 Celebrity Service Manual. Please record the information as referenced in this bulletin in your manual for future use.

INSTRUMENT PANEL: INDICATORS CLUSTER

N: TACHOMETER TEST

Measure: VOLTAGE At: TACHOMETER CONNECTOR (Disconnected) Conditions: - Ignition Switch: RUN - Park Lights: ON

Measure Correct For Diagnosis Between Voltage of Incorrect Results

A(PNK/BLK) Battery See 1 &Ground

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

E (WHT) & C 10 volts or See 3 (BLK) greater Greater than 5

F(GRY)&C volts variable See 4 (BLK) with Dimmer Control

D (BRN) & C Battery See 5 (BLK)

*If all voltages are correct, replace the tachometer.

1. Check the PNK/BLK (39) wire for an open.

2. Check the BLK (150) wire for an open.

3. Check the WHT (121) wire for an open. If OK, see Section 6D.

4. Check the GRY (8) wire for an open (see Section 8A-117).

5. Check the BRN (9) wire for an open (see Section 8A-12).

O: SHIFT INDICATOR WIRE TEST ------------------------- Disconnect connector C3 from the Electronic Control Module (ECM). Put the Ignition Switch in RUN and measure the voltage at connector C3 terminal F6 (see schematic).

- If battery voltage is present, see Section 6E.

- If no voltage is present, check the TAN/BLK and TAN/WHT (456) wire for an open or short to ground (see schematic).

P: SPEEDOMETER AND ODOMETER ARE NOT ACCURATE (J334310-10 Harness Connector available)

1. Disconnect connector C210, Plug in the J33431 Instrument Panel Cluster Tester and connect the J33431-10 harness connector to terminal N and Ground. Turn the Ignition Switch to RUN. Set the Tester Controls to ON, 54 MPH and 6OHz. Observe the Speedometer. It should read 54 mph + 2 mph.

- If the Speedometer reads correctly, check for correct tire size and proper inflation. If tire size and inflation are OK, replace the ECM.

- If the Speedometer does not read correctly replace the Instrument Cluster (see Section 8C).

CIRCUIT OPERATION

If the complete circuit of an indicator is not shown on Instrument Panel schematics, see the circuit referred to for the complete operation of the indicator. Only the indicators and gages that do not appear in other schematics are described in this section.

Oil Indicator

When starting the engine, the OIL Indicator lights as a bulb test. The bulb circuit is case grounded through the Oil Pressure Switch. After the engine starts, and the oil pressure rises above 27 kPa (4 PSI), the Oil Pressure Switch opens. With no path to ground, the OIL Indicator goes out. If the oil pressure fails, the Oil Pressure Switch closes. The OIL Indicator bulb lights for one side is again grounded through the Oil Pressure Switch.

Temperature Indicator

The TEMP Indicator bulb is tested in BULB TEST and START by grounding through the Ignition Switch. The indicator lights in RUN when the engine coolant temperature is above 258 DEGF (126 DEG C) and the Coolant Temperature Switch closes.

Tailgate Ajar Indicator

Voltage is applied at all times through the GAGES Fuse to the TAILGATE AJAR Indicator. When the Tailgate in unlatched, the Tail- gate Ajar Switch is closed. This provides a ground for the TAILGATE AJAR Indicator which allows the bulb to light.

Fuel Gage

The pointer of the Fuel Gage is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the "E " coil and the circuit divides at the opposite end of this coil. One path continues to ground through the "F " coil. Another goes to ground through the variable resistor of the Fuel Gage Sender.

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.