Chart C-12, Cooling Fan Functional Check: Notes

The electric cooling fan is controlled by ECM through fan relay, based on inputs from the coolant and manifold air temperature sensors, A/C control switch, A/C pressure sensor and vehicle speed sensor. ECM controls cooling fan by grounding circuit No. 536 which activates fan relay.

Fan relay is commanded on under the following conditions:

"Scan" tester indicates coolant temperature 103-106°C or greater.
A/C clutch request.
Vehicle speed less than 35 MPH.

Fan relay is commanded on regardless of vehicle speed under the following conditions:

A Code 14 or 15 is set.
"Scan" tester indicates coolant temperature 115-118°C or greater.
A/C pressure is high.

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

With diagnostic terminal grounded, cooling fan control drivers will close. This should energize the fan control relay.
This test checks to see if fault is in wiring to fan, or fan connection.