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HOMESERVICE MANUALSPONTIAC19876000 SAFARIREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISV6/V8 PFI COMPONENT TESTCHART C12 - COOLING FAN CONTROL CIRCUIT (2.8L)CHART C12 - COOLING FAN CONTROL CIRCUIT (2.8L) (1 OF 2)
1987 Pontiac 6000 Safari

Chart C12 - Cooling Fan Control Circuit (2.8L) (1 Of 2)

1987 Pontiac 6000 SafariSECTION Chart C12 - Cooling Fan Control Circuit (2.8L) (1 Of 2)

The electric cooling fan is controlled by the ECM, based on inputs from the coolant temperature sensor, the A/C fan control switch, and vehicle speed sensor. The ECM controls the fan by grounding circuit No. 335, which energizes the fan control relay. Battery voltage is then supplied to the fan motor.

The ECM grounds circuit No. 335, when coolant temperature is over about 223°F (106°C), or when A/C has been turned on. This will cause the fan control switch to open with high A/C pressure, about 200 psi (13.8 kg/cm2 ). Once the ECM turns the relay on, it will keep it on for a minimum of 30 seconds, or until vehicle speed exceeds 70 MPH. Also, if Code 14 or 15 sets, or the ECM is in throttle body back up, the fan will run at all times. On a vehicles not equipped with A/C, circuit No. 732 is jumpered to ground so that the fan does not run at all times.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. With the diagnostic terminal grounded, the cooling fan control driver will close, which should energize the fan control relay.
  2. If the A/C fan control switch or circuit is open, the fan would run whenever the engine is running.
  3. With the A/C clutch engaged, the A/C fan control switch should open when A/C high pressure exceeds about 200 psi (13.8 kg/cm2 ). This signal should cause the ECM to energize the fan control relay.
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