Engine Cooling Fan Buick Skylark VI

APPLICATION

ELECTRIC COOLING FAN APPLICATIONS

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 COMPUTERIZED ENGINE CONTROL section.

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.

CHART C-12, COOLING FAN CHECK 2.0L TURBO - VIN M

Battery voltage for the cooling fan motor is supplied thru relay terminals No. 1 and 5. The cooling fan is turned on when the ECM grounds circuit No. 335.

The ECM may command cooling fan to run when the ignition is off, based on MAT, coolant temperature and engine run time. ECM will ground circuit No. 335 and operates cooling fan for between 20 seconds and 7 minutes after engine is off. This feature is provided to reduce underhood temperature, and prolong turbocharger life.

The ECM will command constant fan if A/C is requested or Code 14 or 15 are set.

Diagnostic Aids

Because the cooling fan can run with ignition off, cooling fan may run for up to 7 minutes.

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.

Cooling Fan Check 2.0L Turbo - VIN M. Scheme 1

CHART C-10, A/C CLUTCH CONTROL 2.0L TURBO - VIN M

When A/C is selected, voltage is supplied to the A/C compressor low pressure switch. If refrigerant pressure is high enough, the low pressure switch will close and complete circuit No. 67 to the normally closed high pressure cut-off switch and to circuit No. 604. The voltage on circuit No. 604 to the ECM is displayed by "SCAN" tester as A/C request "ON" (voltage present), or "OFF" (no voltage present).

When a request for A/C is detected by ECM, ECM will ground circuit No. 459 of the A/C clutch control relay. Relay contacts close and current will flow from circuit No. 604 to circuit No. 59 engaging A/C compressor clutch. A "SCAN" tester will display the grounding of circuit No. 459 as A/C clutch "ON". When ECM detects voltage in circuit No. 604, the cooling fan will also be turned on.

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

1. The ECM will energize the A/C relay ONLY when the engine is running. This test will determine if the relay or circuit No. 459 is at fault.
2. The low pressure and high pressure switches must be closed for the A/C request signal (12 volts) to be present at ECM.
3. A short to ground in any part of A/C request or A/C clutch control circuits could be the cause of blown fuse.
4. With the engine idling and A/C on, ECM should be grounding circuit No. 459 causing test light to be on.
5. This step determines if signal is reaching the low pressure switch on circuit No. 66 from A/C control panel. The signal should be present only when A/C or defrost is requested.

If complaint was insufficient A/C cooling, problem may be caused by an inoperative cooling fan or A/C low or high pressure switches. Engine cooling fan should turn on when refrigerant pressure is high enough to close low pressure switch and energize cooling fan relay through ECM. The A/C clutch will be disengaged if a high power steering pressure is detected by ECM. See CHART C1-E .

A/C Clutch Control 2.0L Turbo - VIN M. Scheme 2

CHART C-1E, POWER STEERING PRESSURE SWITCH (PSPS) CHECK 2.0L TURBO - VIN M

The Power Steering Pressure Switch (PSPS) is normally open to ground, and circuit No. 495 should have near battery voltage. Power steering pressure increases as steering wheel is turned. The PSPS will close (less than 1 volt on circuit No. 495), disengaging the A/C compressor clutch and increasing the idle air rate.

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

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

Scheme 3

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. (Scheme 3): PSPS Check 2.0L Turbo - VIN M

The electric cooling fan is controlled by the ECM through the low or high speed fan relay based on inputs from the coolant temperature sensor, A/C control switch, A/C pressure sensor and the vehicle speed sensor. The ECM controls the cooling fan by grounding circuit No. 536 which turns the relay on. Fan relay will be engaged when

1. Code 14 or 15 is set.
2. Coolant temperature is 217-221°F (103-105°C) or above.
3. A/C clutch is engaged and vehicle speed is less than 35 MPH.
4. A/C pressure is high. The cooling fan will run for about 7 minutes after ignition is turned off.

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

1. With diagnostic terminal grounded, fan control relay should be grounded.
2. This checks if fault is in wiring to fan, or if fan connection is faulty.

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. If engine is overheating and cooling fan is on, check cooling system.

Battery voltage is supplied to fan relay circuit No. 2 and from ignition to circuit No. 250. Grounding relay circuit No. 335 will close relay and supply battery voltage to fan motor. Above 30 MPH, the ECM will remove ground from circuit No. 335. If coolant temperature and A/C pressure switches are open, fan will stop. Fan is energized when

1. A/C is on and vehicle speed is less than 30 MPH.
2. Coolant temperature is greater than 226°F (108°C).
3. Code 14 or 15 is set.

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. If engine is overheating and cooling fan is on, check cooling system.

CHART C-10, A/C CLUTCH CONTROL 2.5L - VIN R & U

When A/C is selected, voltage is supplied to the A/C low pressure switch. If refrigerant pressure is high enough, the low pressure switch will close and complete circuit No. 67 to the normally closed high pressure cut-off switch and to circuit No. 604. The voltage on circuit No. 604 to the ECM is displayed by "SCAN" tester as A/C request "ON" (voltage present), or "OFF" (no voltage present).

When a request for A/C is detected by the ECM, ECM will ground circuit No. 459 of the A/C clutch control relay. Relay contacts close and current will flow from circuit No. 604 to circuit No. 59 engaging A/C compressor clutch. A "SCAN" tester will display the grounding of circuit No. 459 as A/C clutch "ON". When ECM detects voltage in circuit No. 604, the cooling fan will also be turned on.

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

1. The ECM will energize the A/C relay ONLY when the engine is running. This test will determine if relay or circuit No. 459 is at fault.
2. The low pressure and high pressure switches must be closed for the A/C request signal (12 volts) to be present at ECM.
3. A short to ground in any part of A/C request or A/C clutch control circuits could be the cause of blown fuse.
4. With engine idling and A/C on, ECM should be grounding circuit No. 459 causing test light to be on.
5. This step determines if the signal is reaching the low pressure switch on circuit No. 66 from A/C control panel. The signal should be present only when A/C or defrost mode is requested.

If complaint was insufficient A/C cooling, problem may be caused by an inoperative cooling fan or A/C low or high pressure switches. Engine cooling fan should turn on when refrigerant pressure is high enough to close low pressure switch and energize cooling fan relay through ECM. The A/C clutch will be disengaged if high power steering pressure is detected by ECM. See CHART C1-E .

A/C Clutch Control 2.5L - VIN R & U. Scheme 4

CHART C-1E, POWER STEERING PRESSURE SWITCH (PSPS) CHECK 2.5L - VIN R & U

The Power Steering Pressure Switch (PSPS) is normally open to ground, and circuit No. 495 should have near battery voltage. Power steering pressure increases as steering wheel is turned. The PSPS will close (less than 1 volt on circuit No. 495), disengaging the A/C compressor clutch and increasing the idle air rate.

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

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

Scheme 5

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. (Scheme 5): PSPS Check 2.5L - VIN R & U

CHART C-12A, COOLING FAN CHECK FUNCTIONAL CHECK 3.3L - VIN N

The electric cooling fan is controlled by the ECM through a relay based on inputs from the coolant temperature sensor, A/C control switch, A/C pressure switch and the vehicle speed sensor. The ECM controls the cooling fan by grounding circuit No. 535 which turns the relay on.

Cooling fan will run when

1. Coolant temperature is 212°F (100°C) or above.
2. A/C pressure is high.
3. Code 14 or 15, coolant sensor failure exists. NOTE: Test numbers refer to test numbers on diagnostic charts.

1. Grounding diagnostic connector should cause ECM to ground circuit No. 535 and fan should run.
2. Engaging A/C compressor will cause ECM to command operation of the cooling fan through circuits No. 66 and 535.

If there's a complaint of an overheating problem, it must be determined if the complaint was due to an actual boilover, the hot temperature light, or if the temperature gauge indicates overheating. If temperature gauge or light indicates overheating, but no boilover is detected, the temperature gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a "SCAN" tester and comparing its reading with the gauge reading.

If engine is actually overheating and the gauge indicates overheating, but cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced.

Cooling Fan Check Functional Check 3.3L - VIN N. Scheme 6

CHART C-12B, COOLING FAN CHECK NO COOLING FAN 3.3L - VIN N

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

Scheme 7

1. Test light should be on as ignition switch is turned on.
2. Test light should be on as grounding the ALDL turns the Quad Driver Module (QDM) on, providing current path to ground.
3. Test light should be on as terminal is direct from circuit No. 2. (Scheme 7): Cooling Fan Check No Cooling Fan 3.3L - VIN N

CHART C-12C, COOLING FAN CHECK COOLING FAN ON AT ALL TIMES 3.3L - VIN N

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

Scheme 8

1. Coolant fan runs at all times if Codes 14, 15 and/or 66 exists.
2. Circuit No. 535 must be grounded, or Quad Driver Module (QDM) inside ECM is defective if test light is on. (Scheme 8): Cooling Fan Check Cooling Fan On At All Times 3.3L - VIN N

CHART C-10, A/C CLUTCH CONTROL 3.3L - VIN N

The A/C relay is ECM controlled to delay A/C compressor clutch engagement 3 tenths of a seconds after A/C is commanded. This allows the Idle Air Control (IAC) valve to adjust engine idle RPM before A/C clutch engages.

The ECM will temporarily disengage the A/C clutch for a calibrated time for one or more of the following

1. Hot engine start.
2. Wide open throttle (TPS over 90 percent)
3. Power steering pressure high (PSPS closed).
4. Engine RPM greater than about 6000.
5. During IAC valve reset.

The A/C clutch relay will remain de-energized when a Code 66 is present or there is no A/C request signal.

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

1. This test will determine if the relay, circuit No. 459 or ECM is faulty.
2. This step determines if the signal is reaching the ECM through circuits No. 50 and 66 from the A/C control panel. Signal should only be present when A/C or defrost is requested.
3. A short to ground in any part of A/C request system (circuits No. 50, 59 and 66), could be the cause of a blown fuse.
4. The ECM will disengage A/C compressor clutch if a high power steering pressure signal is received by ECM.
5. With engine at idle and A/C on, the ECM should be grounding circuit No. 459. This will cause test light to be on.

If complaint was insufficient A/C cooling, problem may be caused by an inoperative cooling fan. See CHART C-12 .

A/C Clutch Control 3.3L - VIN N. Scheme 9

CHART CE3-A, (CODE 46) POWER STEERING PRESSURE SWITCH CHECK 3.3L - VIN N

The Power Steering Pressure Switch (PSPS) is normally open to ground, and circuit No. 495 should have near battery voltage. Power steering pressure increases as steering wheel is turned. The PSPS will close (less than 1 volt on circuit No. 495), disengaging the A/C compressor clutch and increasing the idle air rate.

A PSPS that will NOT close, or an open in circuits No. 901 or 450, may cause the engine to stall when power steering load is high. A PSPS that will NOT open, or a short to ground of circuit No. 901, may effect engine idle and will not allow for A/C compressor clutch operation.

To set a Code 46, the following conditions must be met

1. Closed PSPS. Low voltage signal on circuit No. 495.
2. Vehicle speed greater than 40 MPH.
3. Both above conditions existing for over 25 seconds. NOTE: Test numbers refer to test numbers on diagnostic charts.

1. This step tests the PSPS for proper operation by using the self-diagnostics system. "LOW" should be displayed when high power steering pressures are created.
2. This step determines if the fault is in the switch or circuit. A jumpered switch connector should indicate high pressure if the circuit is okay. If so, PSPS or connection is faulty.
3. If the display switches to "HI" when circuit No. 495 is grounded, the fault is an open in circuit No. 450.

An intermittent may be caused by a poor connection, broken wire or rubbed through wire insulation. Check harness and connections for backed out terminal BD12, improper mating and broken connector locks. If fault is intermittent, monitor PSPS display while wiggling related wires and connectors to isolate fault.

Power Steering Pressure Switch Check 3.3L - VIN N. Scheme 10

Electric Cooling Fan - "N" Body. Scheme 11

See also:
• CHART C1-E
• CHART C-12