System Operation Description:
Use this procedure under the following situation:
The circuit for the fan override switch is suspected of incorrect operation.
Note: This procedure is intended for troubleshooting a fan override switch that is connected to an ECM input circuit. This procedure is not intended for a fan override switch that is installed in the cooling fan output circuit.
Fan Override Switch
The fan override switch is used to turn on the cooling fan. Using a fan override switch can provide the following benefits:
• Helpful for troubleshooting problems with the cooling fan
• Additional cooling
• Additional braking horsepower under certain operating conditions
The circuit for the fan override switch can be installed on four different inputs. Programming of the “Customer Specified Parameters” is required to select the desired input for the fan circuit. If the “Fan Override Switch” parameter is programmed to “None” (default), this feature is not used. If the “Fan Override Switch” parameter is programmed to one of the available options, then the fan override switch is available. The switch circuit should be connected to the input that was specified. The available options that are for the fan override switch are (J1/P1:7, J1/P1:47, J1/P1:6, J1/P1:46).
Note: The wiring for your particular application may be slightly different. The circuits for the sensor common are used interchangeably by the OEM of the vehicle. The following circuits are common within the ECM:
• The “Input Sensor Common 1” is terminal 18.
• The “Input Sensor Common 2” is terminal 3.
• The “AP Sensor/Switch Sensor Common” is terminal 5.
Test Step 1. Check the Status of the “Fan Override Switch”
A. Connect the electronic service tool to the data link connector.
B. Turn the key switch to the ON position.
C. Monitor the status for the “Fan Override Switch” while the fan override switch is moved to the ON position and the OFF position.
Note: If the status for the “Fan Override Switch” indicates “Not Installed”, then the “Fan Override Switch” parameter has not been programmed.
Expected Result:
The status for the “Fan Override Switch” should be “On” when the switch is in the On position. The status for the “Fan Override Switch” should be “Off” when the switch is in the Off position.
Results:
• OK – The switch is operating normally. STOP.
• Not OK – The ECM is not reading the change in switch status. Proceed to Test Step 2.
Test Step 2. Determine the Configuration of the Fan Override Switch
A. Determine if the fan override switch is wired directly to the ECM or through the J1939 data link.
B. Verify that the “Fan Override Switch” parameter is programmed to reflect the proper wiring.
Expected Result:
The fan override switch is wired directly to the ECM.
Results:
• OK – The fan override switch is wired directly to the ECM. Proceed to Test Step 3.
• Not OK – The fan override switch is wired through the J1939 data link.
Repair: Verify that the “Fan Override Switch” parameter is programmed to “J1939 – Body Controller”, “J1939 – Cab Controller”, or “J1939 – Instrument Cluster”.
Refer to Troubleshooting, “Powertrain Data Link Circuit – Test”.
STOP.
Test Step 3. Check the Electrical
Connectors and the Wiring
A. Thoroughly inspect the J1/P1 ECM connector, the connectors, and the firewall bulkhead connectors. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
B. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the suspect switch circuit.
C. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).
D. Check the harness and the wiring for abrasion and pinch points from the battery to the ECM.
Then, check from the key switch to the ECM.
Refer to Illustration 101 for terminal locations for the ECM.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring should be free of corrosion, abrasion or pinch points.
Results:
• OK – Proceed to Test Step 4.
• Not OK
Repair: Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected.
Verify that the repair eliminates the problem.
STOP.
Test Step 4. Check the Switch Circuit for the ECM
A. Turn the key switch to the OFF position.
B. Install a 140-2266 Cable (Seventy-Pin Breakout) between the J1 and P1 ECM connectors.
C. Fabricate a jumper wire 100 mm (4 inch) long.
Crimp a Deutsch pin to each end of the wire.
D. Insert the jumper wire into the suspect switch socket of the breakout T. Connect the other end of the jumper wire to terminal 5 (AP Sensor/Switch Sensor Common) of the breakout T.
E. Turn the key switch to the ON position.
F. While the status for the “Fan Override Switch” is monitored, remove the jumper wire and then insert the jumper wire.
Expected Result:
The status for the “Fan Override Switch” is “On” when the jumper wire is inserted. The status for the “Fan Override Switch” is “Off” when the jumper wire is removed.
Results:
• OK – The ECM is functioning properly at this time.
Repair: Remove the breakout T and reconnect the J1 and P1 ECM connectors.
Proceed to Test Step 5.
• Not OK – The ECM is not functioning properly.
Repair: Temporarily connect a test ECM. If the problem is resolved with the test ECM, install the suspect ECM. If the problem returns with the suspect ECM, replace the ECM.
Verify that the repair eliminates the problem.
STOP.
Test Step 5. Insert a Jumper Wire at the Switch
A. Turn the key switch to the OFF position.
B. Fabricate a jumper wire 100 mm (4 inch) long.
Crimp a Deutsch pin to each end of the wire.
C. Insert the jumper wire between the two switch terminals of the fan override switch.
D. Turn the key switch to the ON position.
E. While the status for the “Fan Override Switch” is monitored, remove the jumper wire and then insert the jumper wire.
Expected Result:
The status for the “Fan Override Switch” is “On” when the jumper wire is inserted. The status for the “Fan Override Switch” is “Off” when the jumper wire is removed.
Results:
• OK
Repair: Replace the fan override switch.
Verify that the repair eliminates the problem.
STOP.
• Not OK – There is a problem in the wire harness between the fan override switch and the ECM.
Proceed to Test Step 6.
Test Step 6. Insert a Jumper Wire at the Bulkhead Connector
A. Turn the key switch to the OFF position.
B. Fabricate a jumper wire 100 mm (4 inch) long.
Crimp a Deutsch pin to each end of the wire.
C. Insert the wire jumper pin between the terminals for the fan override switch on the engine side of the ECM bulkhead connector.
D. Turn the key switch to the ON position.
E. While the status for the “Fan Override Switch” is monitored, remove the jumper wire and then insert the jumper wire.
Expected Result:
The status for the “Fan Override Switch” is “On” when the jumper wire is inserted. The status for the “Fan Override Switch” is “Off” when the jumper wire is removed.
Results:
• OK – The problem is in the vehicle wiring between the bulkhead connector and the switch.
Repair: Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair.
Verify that the original condition is resolved.
STOP.
• Not OK – The problem is in the vehicle wiring between the bulkhead connector and the ECM.
Repair: Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair.
Verify that the original condition is resolved.
STOP.
