Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
The engine cooling fan is a variable speed fan. The ECM controls the fan speed by sending a pulse width modulated signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is effected by many different conditions and can be adjusted from 10% to 90% duty cycle (PWM), 90% is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. During normal operation the control circuit voltage will be low and near battery voltage when OFF.
Cooling System Connector End Views
Cooling System Description and Operation
Ignition ON, command the cooling fan ON and OFF with a scan tool. Observe that the cooling fan turns ON and OFF with each command.
⇒ | If greater than 1.0 ohm, test the ground circuit for an open/high resistance. |
⇒ | If less than B+, test the battery positive voltage circuit for a short to ground or an open/high resistance. If the COOLFAN fuse is open, test battery positive voltage circuit for a short to ground. |
⇒ | If less than B+, test the control circuit for and open/high resistance. If the circuit tests normal replace the ECM. |
⇒ | If not within specified value, test and replace the cooling fan. |
Install a 60A fused Jumper wire between the cooling fan supply voltage terminal 4 and B+. Momentarily install a jumper wire between the cooling fan low reference terminal 1 and ground. The cooling fan should turn ON.
⇒ | If the function does not perform as specified, replace the cooling fan. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming. |