Circuit Description
The engine control module (ECM) controls both cooling fan motors by controlling 2 drivers, which pull each cooling fan control circuit to ground. The combination of high/low inputs to the cooling fan control module allow OFF, low, medium, and high cooling fan speeds. When the ECM fan control driver is OFF, the cooling fan control module input is high, battery voltage. When the ECM fan control driver is ON, the cooling fan control module input is low, 0 volts. When the fan control 1 and 2 are commanded OFF, neither cooling fan will run. When fan control 2 is ON and fan control 1 is OFF, both fans will run at low speed. When fan control 1 is ON and fan control 2 is OFF, both fans will run at medium speed. Finally, when fan control 1 and 2 are ON, both fans will run at high speed. Both cooling fan motors will begin to run on low whenever the ECT is above 96°C (204°F), A/C is commanded ON with a high side pressure above 1 199 kPa (174 psi) gage pressure or on high if a low/high fault exists in the ECT sensor circuit. DTC P0691 will set if the ECM detects lower than normal feedback voltage when fan control 1 is commanded OFF with the engine cranking/running.
Conditions for Setting the DTC
DTC P0691 will set if fan control 1 feedback voltage is less than 2.6 volts when fan control 1 is commanded OFF when:
| • | The condition exists for longer than 0.5 seconds. |
| • | The engine speed is greater than 40 RPM. |
| • | The main relay voltage is between 7.5-15 volts. |
DTC P0691 diagnostic runs continuously once the above conditions have been met.
DTC P0691 is a type B DTC.
Diagnostic Aids
To locate an intermittent problem, use the scan tool to monitor DTC P0691 LAST TEST with the engine running, ECT below 96°C (204°F), and the A/C relay commanded OFF. Wiggling the wires while watching for a change from PASSED to FAILED may locate the area where a short to ground in the wiring may exist.
