A/C - Intermittent Hot Air or Heat From ECC System
89cadillac07Bulletin No. T-89-91A
File in Group 1
Number 61
Corp. Ref. No. 911101R
Date April, 1989
SUBJECT: INTERMITTENT HOT AIR OR HEAT FROM ECC SYSTEM
MODELS AFFECTED: 1985-1987 DE VILLES AND FLEETWOODS
This bulletin supersedes, Group 1, date 4/89 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~ 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, PN 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.