C15 – Cooling Fan Is Always ON

Probable Causes

The probable root causes are listed in order below:
• OEM vehicle component failure

• PTO mode
• A/C high pressure switch circuit
• Manual fan override switch
• Dyno mode

Recommended Actions

Perform the following diagnostic procedures in order:
1. Check for OEM vehicle component failure.
a. Inspect the J1/P1 ECM connector. Check for a wire that goes into terminal 13 (Output 4) and/or                  terminal 11 (Output 5).
If a wire is not connected to terminal 13 (Output 4) and/or terminal 11 (Output 5), the ECM is not              connected to the cooling fan system. The problem is in the OEM vehicle system.
If a wire is connected to the J1/P1 ECM connector, proceed to Step 4.b.
b. Turn the ignition key to the ON position while the engine is OFF.
c. Connect the electronic service tool to the data link connector.
d. Access the parameter for the “Fan Control Type”.
Ensure that the parameter for the “Fan Control Type” is programmed to On/Off control for an                      On/Off fan or ensure that the parameter for the “Fan Control Type” is programmed to Three-                        Speed Fan control for a three-speed fan.
If the fan is an On/Off fan, proceed to Step 1.e.
If the fan is a three-speed fan, proceed to Step 1.h.
e. Access the “On/Off Cooling Fan” test.
f. Ensure that any fan override switches on the dash are in the OFF position.
g. Listen for the solenoid and/or the relay to click as the test is activated and deactivated.
If the solenoid and/or the relay is clicking, the ECM and the circuit to the solenoid and/or the relay              are operating correctly.

If the solenoid and/or the relay are not clicking, refer to Troubleshooting, “Cooling Fan Circuit and              A/C High Pressure Switch Circuit – Test”.
h. Access the “Three-Speed Fan Slip Output” test.
i. Listen for the Slip Solenoid to click as the test is activated and deactivated.
If the Slip Solenoid is clicking, the ECM and the circuit to the Slip Solenoid are operating correctly.
If the Slip Solenoid is not clicking, refer to Troubleshooting, “Cooling Fan Circuit and A/C High                      Pressure Switch Circuit – Test”.

2. Check the “PTO Activates Cooling Fan” parameter.
Note: If the problem occurs in PTO mode, continue with this step. If the problem does not occur in            PTO mode, skip this step.
a. Connect the electronic service tool to the data link connector.
b. Access the configuration parameters on the electronic service tool.
c. Check the “PTO Activates Cooling Fan” parameter.
d. If the parameter is programmed to “Continuous” the cooling fan will run continuously while the                   engine is in PTO mode.

3. Check the A/C high pressure switch circuit.
a. Connect the electronic service tool to the data link connector.
b. Access the status screen for the “A/C Fan Input”.
If the status screen for the “A/C Fan Input” indicates that the “A/C Fan Input” is disabled, the ECM              is not programmed to use the signal input for the A/C high pressure switch. The ECM will not turn              the fan ON because of a high A/C pressure. The problem is in the OEM vehicle system.
If the status screen for the “A/C Fan Input” indicates that the “A/C Fan Input” is OFF, ON or                              COUNTING, the ECM is programmed to turn the fan ON because the A/C high pressure switch                  circuit is open. If the status screen for the “A/C Fan Input” indicates OFF, ON or COUNTING,                          proceed to Step 3.c.

c. Start the engine. Allow the engine to idle.
Watch the status screen on the electronic service tool that indicates the status of the “A/C Fan                    Input”.
If the status screen indicates OFF at any time and the fan is still ON, the A/C high pressure switch              circuit is operating correctly.
The problem is in the OEM vehicle system.
If the status screen indicates ON and/or COUNTING, the ECM is turning the fan ON because the                A/C high pressure switch circuit is open. Refer to Troubleshooting, “Cooling Fan Circuit and A/C                  High Pressure Switch Circuit – Test”.

4. Check the Manual Fan Override Switch.
a. Connect the electronic service tool to the data link connector.
b. Access the parameter for the “Fan Override Switch”.
c. Check the parameter for the “Fan Override Switch”. Ensure that the fan override switch is                                programmed to one of the options for Input Selections.
If the parameter is programmed to one of the four available outputs, check the input for the fan                   override switch. The four available options for Input Selections are the following connections:
• J1/P1:6
• J1/P1:7
• J1/P1:46
• J1/P1:47
d. Access the status screen for the “Fan Override Switch”.
If the status is ON, either the manual fan override switch is ON or there is a short in the circuit for              the “Fan Override Switch”. Refer to Troubleshooting, “Cooling Fan Circuit and A/C High Pressure                Switch Circuit – Test”.

5. Dyno Mode will cause the cooling fan to run continuously. During a dyno run, the ECM should
be in Dyno Mode.
Dyno Mode will only be active for 30 minutes.
After 30 minutes, the ECM will exit Dyno Mode.
Dyno Mode can only be enabled with the electronic service tool.

 

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