Engine Cooling Fan Chevrolet Cavalier II

DESCRIPTION

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 ENGINE PERFORMANCE section.

All FWD and some RWD vehicles use an electric cooling fan. The electric cooling 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, ECM receives a signal on this line and turns cooling fan on. 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

See trouble shooting charts for cooling fan diagnosis.

CHART C-12: COOLING FAN (2.0L VIN K)

Battery voltage for cooling fan motor is supplied through relay terminal No. 1. Ignition voltage to energize relay is supplied to relay terminal No. 5. Cooling fan is turned on when the ECM grounds circuit No. 335.

When engine is running, ECM will energize cooling fan relay if coolant temperature sensor Code 14 or 15 has been set or if A/C is turned on and vehicle speed is less than 70 MPH. Cooling fan is also energized when coolant temperature is greater than 223°F (106°C).

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 boilover is in evidence, inspect the gauge/light circuit for malfunction.

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

Scheme 1

Scheme 2

CHART C-10: A/C CLUTCH CONTROL (2.0L VIN K)

When A/C mode is selected, ignition battery voltage is supplied through the A/C request circuit to ECM. With sufficient A/C refrigerant charge, the low pressure switch will be closed and complete the circuit to the closed high pressure cut-off switch and to circuits No. 603 and No. 604. When an A/C request is sensed by ECM, ECM will ground circuit No. 359, energizing A/C clutch control relay, and voltage will be supplied from circuit No. 604 to circuit No. 59 and engages the A/C compressor clutch. A "Scan" tester will display the grounding of circuit No. 459 as A/C clutch on. Cooling fan will also be turned on when ECM senses voltage to circuit No. 603.

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

1. The A/C compressor clutch should not engage until 3 seconds after engine is started.
2. Refer to «A/C-HEATER SYSTEMS - MANUAL»(/chevrolet/cavalier/ii-1988-1994/remont/manual-hvac-system/#ac-heater-system-manual) article in this section.
3. A blown A/C-heater fuse could be caused by a short to ground from the ignition switch to the compressor.

Both pressure switches are located at the rear of A/C compressor. The low pressure switch connector can be identified by a Blue insert and the high pressure switch connector by a Red insert. A/C clutch control relay is located on the right shock tower.

Low pressure switch closes at about 47 psi (3.3 kg/cm 2 ) and opens at about 8 psi (.6 kg/cm 2 ). High pressure switch opens at 430 psi (30 kg/cm 2 ) and disengages compressor clutch to prevent system damage.

Scheme 3

Scheme 4

CHART C-12: COOLING FAN (2.2L VIN G)

Battery voltage is supplied to cooling fan motor through terminal No. 1 of cooling fan control relay. Voltage from ignition system is supplied to cooling fan control relay terminal No. 5. The ECM grounds circuit No. 335 energizing the cooling fan control relay when

1. Code 14 or 15 is set.
2. A/C is engaged.
3. Coolant temperature greater than 226°F (108°C).

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 boilover is in evidence, inspect the gauge/light circuit for malfunction.

If vehicle is overheating and the gauge or light indicates the same, but the 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 5

Scheme 6

CHART C-10: A/C CLUTCH CONTROL (2.2L VIN G)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement approximately 4/10 of a second after A/C is turned on. This allows the Idle Air Control (IAC) valve to adjust engine RPM before A/C clutch engages.

The ECM will also disengage A/C clutch if high power steering pressure is present, engine overheating or WOT. The ECM provides a ground path for A/C clutch relay through circuit No. 459.

If A/C pressure is less than 40 psi (2.8 kg/cm 2 ), the low pressure switch will open. If A/C pressure is more than 440 psi (31 kg/cm 2 ), the high pressure switch will open.

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

1. The ECM will only energize A/C relay when engine is running. This will determine if relay or circuit No. 459 is faulty.
2. For A/C clutch to engage, low pressure switch must be closed, providing 12 volts to relay. High pressure switch must be closed so A/C request (12 volts) will be present at ECM.
3. Determines if A/C control panel request signal is reaching the ECM on circuit No. 604. This signal should only be present when A/C or defrost is selected.
4. A blown fuse can be caused by a short to ground in circuits No. 604, No. 59, A/C request circuit or A/C clutch.
5. With A/C on and engine idling, ECM should be grounding circuit No. 459. This will cause test light to illuminate.

If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan or A/C pressure fan switch. The engine cooling fan should turn on when A/C pressure exceeds a value to open the switch, which causes the ECM to energize cooling fan relay.

Scheme 7

Scheme 8

CHART C-12, COOLING FAN (3.1L VIN T)

The ECM controls cooling fan with inputs from A/C pressure sensor, coolant temperature sensor and vehicle speed. The ECM grounds circuit No. 335 to energize fan control relay. Battery voltage is then supplied to the fan motor.

The ECM grounds circuit No. 335 when A/C has been requested, coolant temperature is greater than 228°F (109°C) or when A/C pressure sensor indicates approximately 200 psi (14.1 kg/cm 2 ). When ECM energizes the fan control relay, it will run for at least 30 seconds or until vehicle speed exceeds 70 MPH. If Code 14 or 15 is present, ECM will run fan continuously.

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

1. With system in field service mode, cooling fan control driver will close and energize fan control relay.
2. If A/C fan control switch or circuit is open, cooling fan will run continuously when A/C is requested.
3. With A/C clutch engaged, A/C fan control switch should open when A/C high pressure exceeds 200 psi (14.1 kg/cm 2 ). This will cause the ECM to energize fan control relay.
4. Code 66 will set when A/C pressure sensor is disconnected. After completing this step, clear codes.

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

If vehicle is overheating and the gauge or light indicates the same, but the 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 9

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

Scheme 10

1. Battery voltage should be present on circuits No. 2 and No. 532 with ignition on.
2. This checks ECM's ability to ground circuit No. 335. The SERVICE ENGINE SOON light should be flashing at this time. If SERVICE ENGINE SOON light is not illuminated, refer to ENGINE PERFORMANCE section.
3. If cooling fan does not run at this point, check circuit No. 150 or 702 is open or cooling fan motor is faulty.

CHART C-10, A/C CLUTCH CONTROL (3.1L VIN T)

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement approximately 3/10 of a second after A/C is turned on. This allows the Idle Air Control (IAC) valve to adjust engine RPM before A/C clutch engages.

The ECM will disengage A/C clutch if high power steering pressure is present, engine overheating, WOT or IAC reset. The ECM provides a ground path for A/C clutch relay through circuit No. 459.

A/C clutch will remain disengaged if Code 66 is present. If A/C pressure is less than 44 psi (3.1 kg/cm 2 ), the low pressure switch will open. If A/C pressure is greater than 430 psi (30 kg/cm 2 ), the high pressure switch will open. If ECM sees high power steering pressure, A/C clutch will be disengaged by ECM.

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

Scheme 11

Scheme 12

1. ECM will only energize A/C relay when engine is running. This test will determine if relay or circuit No. 459 is faulty.
2. Determines if signal is reaching ECM through circuit No. 66 from the A/C control panel. Signal should only be present when A/C mode or defrost mode has been selected.
3. If ECM is receiving a high power steering pressure signal, A/C clutch will be disengaged by ECM. NOTE: Test numbers refer to test numbers on diagnostic charts.
4. This checks if pressure transducer is out of range causing A/C clutch to disengage.
5. With engine off and field service mode activated, ECM should ground circuit No. 459 causing test light to illuminate.

If complaint was insufficient cooling, problem may be caused by an inoperative cooling fan or A/C pressure fan switch. Engine cooling fan should turn on when A/C pressure exceeds a value to open the switch, which causes ECM to energize cooling fan relay.

Scheme 13

CHART C-1E, P/S PRESSURE SWITCH (3.1L VIN T)

The Power Steering Pressure Switch (PSPS) is normally open to ground. Circuit No. 495 should have near battery voltage. Power steering pressure increases as steering wheel is turned. The PSPS will close (less than one volt on circuit No. 495), disengaging A/C compressor clutch and increasing idle air rate.

A PSPS that will NOT close or an open in circuits No. 495 or 450, may cause engine to stall when power steering load is high. A PSPS that will NOT OPEN or a short to ground in circuit No. 495, may affect engine idle and will not allow A/C compressor clutch operation.

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

Scheme 14

1. Different makes of "Scan" testers may display the state of PSPS switch in different ways. Refer to operation manual for your particular tester.
2. This step checks if circuit No. 495 is shorted to ground.
3. This step simulates a closed PSPS switch. 1269 is not shorted to battery voltage. If circuit is not shorted, PCM is internally shorted.
4. If test light turns off after disconnecting PCM, ensure circuit No. 1270 is not shorted to battery voltage. If circuit is not shorted, PCM is internally shorted.

See also:
• A/C-HEATER SYSTEMS - MANUAL