INTERMITTENT HOT AIR OR INCREASED HEAT FROM ECC SYSTEM

MODELS AFFECTED: 1985-1987 DE VILLES AND FLEETWOODS

This bulletin supersedes bulletin T-89-91, Group 1, which should be discarded. The CTS part number in step 1b was incorrect.

Some 1985-1987 Fleetwoods and DeVilles may experience a condition of hot air out of the heater or A/C ducts intermittently. This may be caused by a poor connection, or faulty Coolant Temperature Sensor (CTS).

Engine coolant temperature is used by the BCM to help determine air mix door position. If the BCM sees a low coolant sensor reading, it moves the air mix door more toward the max heat position to compensate for a cooler heater core.

To repair this condition the following procedure should be used during the condition*: Enter BCM parameters and select P.2.1.

1. If the car has been running for more than 10 minutes and the CTS reading is less than 70 DEG Celsius, perform the following:

a. Disconnect and jumper the CTS connector leads together; P.2.1 should read 151. If the reading is below 150, there is a high resistance point in the circuit. Measure resistance in circuits 410 and 476 from the ECM to CTS. Check the wire showing resistance above 1 ohm for damage or a poor connection.

b. If the jumpered CTS circuit reading is 151, replace the sensor, P/N 25036979. On 1985 models when replacing the sensor, replace the CTS connector with metropak connector, P/N 12046623. Parts are currently available from GMSPO.

2. If the CTS reading is correct during the condition, perform the ECC diagnosis in Sections 1C, 8A-62, or 8A-64.

For warranty purposes use Labor Operation J6368 at .5 hour.

* This procedure will only work when the vehicle exhibits this condition. To duplicate this condition it may help to cycle the CTS and ECM connectors, and wiggle circuits 410 and 476 wiring.

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.