Chart C-12, Cooling Fan Circuit Diagnosis (1 Of 2) 3.1L: Notes

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ECM controls electric cooling fan(s) based on inputs from coolant temperature sensor, A/C request, refrigerant fan request switch and vehicle speed. ECM energizes fan(s) by grounding circuits No. 335 and No. 473, which closes cooling fan relay(s). Battery voltage is supplied to cooling fan(s) when energized by the ECM. ECM grounds circuit No. 335 (puller fan) when coolant temperature is approximately 223°F (106°C) or when A/C has been requested and refrigerant fan request switch opens with high A/C pressure, approximately 200 psi (14.1 kg/cm² ). Pusher fan relay is grounded when coolant temperature is approximately 217°F (103°C) and/or puller fan is energized for A/C pressure.

NOTE: Test numbers refer to test numbers on diagnostic charts.

With ALDL diagnostic terminal grounded, cooling fan driver closes and energizes fan control relay.
If A/C fan request switch or circuit is open, cooling fan operates whenever A/C is operating.
With A/C requested and 45 seconds after request is removed, A/C refrigerant fan request switch should open when A/C high pressure exceeds approximately 200 psi (14.1 kg/cm² ). This signal should cause ECM to energize fan control relays(s).
This test checks if cooling puller and pusher fan relay(s) (circuits No. 335 and 473) are shorted to ground. This condition would cause fans to be energized continuously.