SER. MAN. UPDATE SEC. 8A ELECT. GAUGE DIAG. REVISED

SUBJECT: SERVICE MANUAL UPDATE - SECTION 8A ELECTRICAL - (REVISED GAUGE AND INDICATOR DIAGNOSTIC TEXT)

VEHICLES AFFECTED: 1988-90 'L'

The 1988. 1989 and 1990 Chevrolet Corsica/Beretta Service Manuals contain inaccurate coolant temperature gauge and indicator information in Section 8A. Please write in the Troubleshooting Hints section in Section 8A-81 of the above Service Manuals to ignore the coolant temperature gauge and indicator diagnostic text and follow the Service Bulletin for gauge and indicator problem diagnosis. Please insert pages 0 thru 3 of the Service Bulletin into Section 8A-81 of your copies of the 1988, 1989 and 1990 Chevrolet Corsica/Beretta Service Manuals. Also make the following changes to your copies of the 1988 and 1989 Chevrolet Corsica/ Beretta Service Manuals.

Year Old Page Remove New Page Add ---- -------------- ----------- 1988 8A-80-1 8A-30-1 1989 8A-80-1 8A-80-1 1989 8A-81-3 8A-81-3

SYSTEM CHECK

o Put the Ignition Switch in BULB TEST. The Temperature Gage should read HOT.

SYMPTOM TABLE

SYMPTOM FOR DIAGNOSIS ------------------ --------------------------------------- Coolant Temperature Do Test B (also see Test A terminal A) Gage indicates hot with engine cool and Ignition Switch in RUN

Coolant Temperature Do Test C (also see Test A terminal A) Gage indicates cold at all times

Coolant Temperature Do Test D (also see Test A terminal A) Gage is inaccurate

Coolant Temperature Do Test E (also see Test A terminal U) Indicator lights when engine coolant is not overheated

Coolant Temperature Do Test F (also see Test A terminal U) Indicator does not Light with engine coolant overheated

Coolant Temperature Do Test G (also see Test A terminal A) Gage does not read Hot in BULB TEST

B: COOLANT TEMPERATURE GAGE SHORT TEST -------------------------------------- Disconnect the Coolant Temperature Sender/ Switch connector and turn the Ignition Switch to RUN.

o If the Coolant Temperature Gage reads Cold, replace the Coolant Temperature Sender/Switch.

o If the Coolant Temperature Gage does not read Cold, check the DK GRN (35) wire for a short to ground (see schematic). Replace the Instrument Cluster if wire is good (see Section 8C).

C: COOLANT TEMPERATURE GAGE OPEN TEST ------------------------------------- Disconnect the Coolant Temperature Sender/ Switch connector. Jumper the DK GRN (35) wire to ground and turn the Ignition Switch to RUN.

o If the Coolant Temperature Gage reads Hot, replace the Coolant Temperature Sender/ Switch.

o If the Coolant Temperature Gage still reads cold, check the DK GRN (35) wire, and Gage connections for an open. If OK, re- place the Instrument Cluster (see Section 8C).

D: COOLANT TEMPERATURE GAGE ACCURACY TEST ------------------------------------------ Disconnect the Coolant Temperature Sender/ Switch connector. Connect one red clip lead of the J-33431 tester to the harness connector DK GRN (35) wire, and the other red clip lead to ground. Adjust the resistance dials of the tester to 1400 ohms and then to 55 ohms. The Coolant Temperature Gage should show Cold and then Hot.

o If the Coolant Temperature Gage reads correctly, the wiring and Gage are good. Replace the Coolant Temperature Sender/Switch.

o If the Gage is not correct, check the Gage connection and the DK GRN (35) wire for high resistance. If OK, replace the Instrument Cluster (see Section 8C).

E. COOLANT TEMPERATURE INDICATOR SHORT TEST -------------------------------------------- Disconnect the Coolant Temperature Switch Connector and turn the Ignition Switch to RUN.

o If the Indicator stays on, check the DK GRN/ WHT (35) wire for a short to ground.

o If the Indicator goes out, replace the Coolant Temperature Switch.

F. COOLANT TEMPERATURE INDICATOR OPEN TEST --------------------------------------------- Connect: FUSED JUMPER

AT:COOLANT TEMPERATURE SWITCH CONNECTOR (Disconnected)

Condition:

o Ignition Switch: RUN

Jumper Correct For Between Result Diagnosis ----------- ------- ---------- B (DK GRN/ Coolant See 1 WHT) & Temperature Ground Indicator comes on

o If the result is correct, replace Coolant Temperature Sender/Switch.

1 Check DK GRN (35) wire and Instrument Cluster Printed Cluster for an open.

G: IGNITION SWITCH TEST ------------------------ Measure: RESISTANCE AT:IGNITION SWITCH (Disconnected) Condition: o Ignition Switch: BULB TEST and START

Measure Correct For Between Resistance Diagnosis ------- ---------- --------- C1/G1 & 0 ohms See 1 Ground

o If the resistance is correct, check/repair DK GRN (35) wire for an open (see schematic). If OK, replace the Instrument Cluster (see Section 8C).

1 Replace the Ignition Switch.

CIRCUIT OPERATION

Coolant Temperature Indicator

The Coolant Temperature Indicator warns the driver of high coolant temperature. With the Ignition Switch in RUN, BULB TEST or START, voltage from Fuse 9 is applied to the Coolant Temperature Indicator. In RUN, the bulb can be grounded through the Coolant Temperature Switch. The Switch closes when the coolant temperature exceeds 258 F (126 C). The light glows.

Coolant Temperature Gage

The Coolant Temperature Gage is operated by two coils. Battery voltage is applied to both coils in series. The Junction between the two coils is grounded through the Coolant Temperature Sender. This has 55 ohms resistance at 260 F (hot coolant) and its resistance increases at lower temperatures. Resistance is approximately 1400 ohms at 100 F. This causes the currents in the coils to vary and this moves the pointer. In BULB TEST or START, the coolant temperature input is grounded through the Ignition Switch forcing the gage to read Hot as a gage check.

BULB LOCATION (See Figure)

A RH Turn Indicator B LOW COOLANT Indicator D Fasten Belts Indicator E BRAKE Indicator F LH Turn Indicator G SERV. ENG. SOON Indicator H SHIFT Indicator (Manual Transaxle) I Not Used J Coolant Temperature Indicator K Cluster Illumination

CONNECTOR (See Figure)

A Coolant Temperature Gage Input N Not Used B SERV. ENG. SOON Input 0 Ground C Oil Pressure Input P Ignition Input D Hi Beam Input Q Not Used E BRAKE Input R Not Used F SHIFT Input S Ground G LH Turn Signal Input T Illumination Input H Fasten Belts Inputs U Coolant Temperature Indicator Input I LOW COOLANT Input V Tachometer Ignition Input J RH Turn Signal Input W Engine Speed Input K Speedometer Ignition Input X Not Used L Vehicle Speed Input Y Not Used M Speedometer Ground Z Fuel Gage Sender Input

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.