Circuit Description
The following DTCs are for the cooling fan relay control circuits controlled by the engine control module (ECM):
| • | DTC P0480--low speed cooling fan relay control circuit |
| • | DTC P0481--high speed cooling fan relay control circuit |
Ignition 1 voltage is supplied to the cooling fan 1 relay from the IGN E fuse. The ECM controls the low speed cooling fan relay by grounding the low speed cooling fan relay control circuit.
Ignition 1 voltage is supplied to the cooling fan 2 relay from the IGN E fuse. The ECM controls the low speed cooling fan relay by grounding the low speed cooling fan relay control circuit.
The ECM grounds the cooling fan relay control circuits through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON, the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.
The ECM will monitor the control circuit for the following:
| • | A short to ground |
| • | A short to voltage |
| • | An open circuit |
| • | An open relay coil |
| • | An internally shorted or excessively low resistance relay coil |
When the ECM detects any of the above conditions, the DTC will set and the effected driver will be disabled.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
DTC P0481 Cooling Fan Relay 2 and 3 Control Circuit
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The system voltage is between 9-18 volts. |
Conditions for Setting the DTC
| • | An improper voltage level has been detected on the cooling fan relay control circuit. |
| • | The condition is present for at least 30 seconds. |
Action Taken When the DTC Sets
| • | The ECM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The ECM will store the conditions that were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The ECM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
| • | If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections . |
| • | Review the Freeze/Failure Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be occurs. |
| • | If the IGN E fuse is open, the DTC U0107 will be set as current DTC. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Listen for an audible click when the cooling fan relay operates. Command both the ON and OFF states. Repeat the commands as necessary. The appropriate cooling fan relay is the cooling fan relay that set the DTC.
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Listen for an audible click when the cooling fan relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
Does the appropriate cooling fan relay turn ON and OFF with each command? | Go to Diagnostics Aids | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 8 | |
4 |
Does the test lamp turn ON and OFF with each command? | Go to Step 9 | Go to Step 5 |
5 | Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 6 |
6 | Test the control circuit of the appropriate cooling fan relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 10 |
7 | Test the control circuit of the appropriate cooling fan relay for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 10 |
8 | Repair the ignition 1 voltage circuit of the appropriate cooling fan relay. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 13 | -- |
9 | Inspect for poor connections at the appropriate cooling fan relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
10 | Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
11 | Replace the appropriate cooling fan relay. Refer to Cooling Fan Relay Replacement . Did you complete the replacement? | Go to Step 13 | -- |
12 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | -- |
13 |
Does the DTC reset? | Go to Step 2 | System OK |
