SERV MANUAL UPDATE-SEC.6E3 DRIVEABILITY & EMISSIONS

SUBJECT: SERVICE MANUAL UPDATE - SECTION 6E3 - DRIVEABILITY AND EMISSIONS ECM CONTROLLED HOT LIGHT DIAGNOSIS CHART

VEHICLES AFFECTED: 1989-91 A,N, 3300 ENGINE (VIN 'N')

The ECM Controlled Hot Light Chart C-16 was inadvertently omitted from Section 6E3 "Driveability and Emissions" of the 1989-91 "A" car and the 1990 "N" car Service Manuals for vehicles equipped with a 3300 (VIN N) engine.

Use the attached pages to diagnose a Coolant Temp/Hot Light Circuit for the vehicles involved.

CHART C-16 ECM CONTROLLED "TEMP"/HOT LIGHT CIRCUIT 3300 (VIN N) (PORT)

Circuit Description:

The "Temp" light is powered through the gages fuse by ignition #1. The ECM energizes the bulb by supplying a path to ground through Quad-Driver module.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. With the ignition "ON" and engine "OFF," the ECM should be grounding CKT 35.

2. The "Temp" light should only be "ON" while the engine is running and the coolant temperature is 123 C (253 F) or higher.

Diagnostic Aids:

The coolant temperature sensor, in rare cases, may fail to indicate the correct engine coolant temperature without setting a malfunction code. This could result in turning "ON" the "Temp" light without having an overheating condition. It could also result in overheating without the "Temp" light being turned "ON." See "Coolant Sensor Temperature vs. Resistance Values" Diagnostic Aids table on Code 15 chart or compare coolant temperature reading on the Tech I with actual coolant temperature. Replace coolant temperature sensor if mis-scaled.

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.