Engine Cooling Fan Buick Electra Park Avenue

APPLICATION

ELECTRIC COOLING FAN APPLICATIONS

DESCRIPTION

All FWD and some RWD vehicles use an electric cooling fan. This fan is used for engine and A/C condenser cooling and operates when A/C is on and if engine overheats.

OPERATION

All electric cooling fans operate when engine coolant temperature exceeds a certain value. The ECM completes ground path for the cooling fan relay. Relay contacts then close and complete circuit between fusible link and fan motor. When the engine cools, the switch opens and fan stops. If coolant sensor fails, the ECM will command constant fan operation.

A/C equipped vehicles have a separate signal line to the ECM for fan control. When A/C control switch is "ON", and A/C system low pressure switch is closed, the ECM receives a signal on this line and turns on the cooling fan. The compressor clutch does not have to engage for ECM to turn fan on.

On some models, when engine is off, ECM may turn on the fan relay and run fan for up to 7 minutes. This occurs if hot conditions were present while engine was running. Hot conditions are based on Manifold Absolute Temperature (MAT) signal to ECM, coolant temperature and time from start.

TROUBLE SHOOTING

Note. This article contains test charts that are part of General Motors Computerized Engine Controls. Only those charts required to test electric cooling fans are included. Other diagnostic codes may appear while performing electric cooling fan diagnosis. For complete information on General Motors Computerized Engine Control systems, see appropriate article in ENGINE PERFORMANCE section.

CHART C-12A, FAN FUNCTIONAL CHECK (3.8L)

Battery voltage for the cooling fan motor is supplied through a fusible link to circuit No. 2 to the relay(s). The relays are energized when current flows to ground through the Quad Driver Modules (QDM) in the ECM.

The ECM energizes the low speed relay through circuit No. 535 when coolant temperature reaches 214°F (101°C). The cooling fan will be turned off when coolant temperature falls below 210°F (99°C), or ignition is turned off. The low speed fan will run any time A/C is requested.

The ECM or the A/C high pressure switch will energize the high speed relay. If A/C refrigerant pressure reaches 275 psi (19 kg/cm 2 ) or coolant temperature exceeds 226°F (108°C), the high speed relay will operate cooling fan at high speed.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Grounding the ALDL connector will cause the ECM to ground circuit No. 536. Cooling fan should run at high speed.
2. By ungrounding the ALDL connector and disconnecting the coolant temperature sensor connector will cause the ECM to think coolant is -38°F (-39°C) and cause a rich fuel mixture. "SCAN" should display a coolant temperature of -38°F (-39°C) and coolant fan should run on low speed. "SCAN" should display "FAN 1 ON".
3. When jumpering coolant temperature sensor wires together, "SCAN" should display coolant temperature of 304°F (151°C). Fan No. 1 will be on. Fan No. 2 will be on momentarily.
4. Jumpering A/C pressure switch harness will cause coolant fan(s) to run on high speed.
5. This step will see if the ECM monitors the coolant temperature signal properly. Any time the coolant temperature exceeds 214°F (101°C), unless vehicle speed exceeds 35 MPH, the ECM should turn on the low speed fan by grounding circuit No. 535. If coolant temperature should continue to climb above 226°F (108°C), the high speed fan should come on. A hot soak condition, key on engine off, will not cause cooling fan operation.

Diagnostic Aids

If an overheating condition is suspected, verify if this is due to actual boil over. If gauge or light indicates an overheat condition, and no boil over is in evidence, inspect the gauge/light circuit for malfunction.

If vehicle is overheating and the gauge or light indicates the same, but cooling fan is not coming on, check coolant sensor temperature using a "SCAN" tester. Sensor may have shifted calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.

Scheme 1

Scheme 2

CHART C-12B, FAN ON ALL TIMES (3.8L)

Note. Test numbers refer to test numbers on diagnostic charts.

Scheme 3

1. This step checks to see if circuit No. 535 is shorted to ground.
2. This step checks to see if circuit No. 536 is shorted to ground. A test light on indicates a short to ground. Steps 3) and 4) will isolate fault.
3. If test light is off after disconnecting ECM, ensure circuit No. 535 is not shorted to battery voltage. If NOT shorted to battery voltage, ECM is shorted internally.
4. If test light is off after disconnecting ECM, ensure circuit No. 536 is not shorted to battery voltage. If NOT shorted to battery voltage, ECM is shorted internally.

CHART C-12C, NO LOW SPEED FAN (3.8L)

Note. Test numbers refer to test numbers on diagnostic charts.

Scheme 4

1. This step checks for battery voltage at relay harness connector.
2. Jumpering terminal No. 1 to 4 by-passes relay, causing cooling fan to run. If fan does not run, wiring and/or fan motor are defective.
3. Grounding the test terminal should cause ECM to ground circuit No. 535. Test light should come on.
4. This step checks for battery voltage and ground at fan motor. A test light on indicates a faulty fan motor connection or fan motor.

CHART C-12D, NO HIGH SPEED FAN (3.8L)

Note. Test numbers refer to test numbers on diagnostic charts.

Scheme 5

1. Test light should be on. Terminal No. 2 has battery voltage when ignition is on.
2. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
3. Checks circuit No. 536 back to ECM. If circuit No. 536 is okay, relay is faulty.
4. Checks wiring to coolant fan. If wiring is okay, fan motor connection or motor is faulty.

SYSTEM OPERATION

Two cooling fans are used. The Electronic Control Module (ECM) contains 2 cooling fan control outputs, one for high speed and one for low speed. When ECM low speed output is activated, it grounds the low speed cooling fan relay located on left side of engine compartment in front of strut tower. When relay is grounded, this completes the circuit to the cooling fan. Current is passed through cooling fan resistor to provide low speed operation of cooling fan. For high speed fan operation, high speed cooling fan relay is grounded by ECM and provides operation of cooling fans.

The ECM controls cooling fan operation by signals received from coolant temperature sensor and refrigerant high side temperature sensor. Coolant temperature sensor is connected directly to ECM and refrigerant high side temperature sensor is connected to Body Computer Module (BCM). Temperature sensor signal is processed by BCM and sent to ECM.

TROUBLE SHOOTING HINTS

Note. Ensure no diagnostic codes exist or diagnostic system can be entered prior to testing. For diagnostic code information, see appropriate article in ENGINE PERFORMANCE section. manual. Check the following prior to performing system check.

1. If cooling fans do not operate, check No. 6 fuse (in fuse block near steering column) and fusible link. Fusible link (Red wire) is located near junction block at center of firewall.
2. If only one cooling fan operates, check cooling fan wiring, cooling fan and cooling fan relay.
3. If cooling fans operate in high speed only, check cooling fan resistor. Resistor is located near cooling fans.

SYSTEM CHECK

1. With engine idling, note that cooling fan operates at low speed after a few minutes.
2. With engine idling, restrict air flow through half of the radiator. Cooling fan should then operate at high speed after a few minutes.
3. Remove restriction from radiator. Cooling fan should return to low speed after a few minutes.
4. If cooling fan did not operate correctly, perform proper test. See SYSTEM DIAGNOSIS in this article.

SYSTEM DIAGNOSIS

Note. Ensure no diagnostic codes exist or diagnostic system can be entered prior to testing. For diagnostic code information, see appropriate article in ENGINE PERFORMANCE section.

Perform proper test according to cooling fan operation.

Scheme 6

Note. (Scheme 7), (Scheme 8), and (Scheme 9) are flow charts.

Scheme 7

Scheme 8

Scheme 9

Cooling Fan Wiring Diagram (DeVille & Fleetwood). Scheme 10

Cooling Fan Wiring Diagram (Electra, Park Avenue, Ninety Eight & Touring Sedan). Scheme 11