Circuit Description
The powertrain control module (PCM) sends a pulse width modulation (PWM) signal of 0-12 volts via the cooling fan clutch control circuit to the cooling fan relay. The PCM monitors the cooling fan clutch control circuit during vehicle operation. When the cooling fan clutch is commanded on by the PCM, the control circuit is at a low voltage. When the cooling fan clutch is commanded off, the control circuit is near battery voltage. The PCM uses this PWM to control the position of the oil control valve located inside the cooling fan clutch. If during operation, the PCM detects an improper circuit condition on the cooling fan clutch control circuit DTC P0480 will set.
Conditions for Running the DTC
| • | The engine speed is greater than 400 RPM. |
| • | The ignition voltage is greater than 10 volts and less than 18 volts. |
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the relay and the actual state of the control circuit do not match. |
| • | The above condition is present for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM stores the conditions present when the DTC sets as Freeze Frame/Failure Records data. |
| • | The PCM commands the cooling fan clutch to 100%. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after the third consecutive trip the diagnostic has 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 Clear DTC Information function. |
Diagnostic Aids
| • | An inline connector could cause an intermittent DTC. Ensure to test for poor connections and pin retention at all inline connectors. Refer to system schematics for connectors and locations. |
| • | If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Disconnect the harness connector of the cooling fan from the shroud. Inspect the exposed wires between the harness connector and the tubing. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step ensures that the DTC has failed this ignition cycle. If the scan tool displays Passed, then the answer is No.
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The cooling fan noise should increase as the cooling fan clutch engages. It can take up to 2 minutes for full cooling fan clutch engagement. If cooling fan clutch is previously fully engaged, then there will not be a noticeable change in cooling fan noise. Compare noise to a known good vehicle. If fan noise is louder than the known good vehicle, then answer Yes.
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In the previous step the cooling fan clutch was fully engaged. This step tests to ensure that the cooling fan clutch will disengage. A noticeable noise difference should be heard between a fully engaged cooling fan clutch and a disengaged cooling fan clutch. The cooling fan clutch is completely disengaged when the excessive fan noise is not heard.
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Tests for the ability of the PCM to control fan speed. If answer to question is Yes, ensure to refer to all Diagnostic Aids.
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Verifies the ignition 1 voltage circuit of the cooling fan relay.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views | ||||
1 | Did you perform the Engine Cooling Diagnostic System Check? | -- | Go to Step 2 | |
Does the scan tool indicate the DTC Failed this ignition cycle? | -- | Go to Step 5 | Go to Step 3 | |
|
Important: P0480, for 5.3l (LM4), will set when the cooling fan relay is disconnected.
Does the cooling fan clutch engage? | -- | Go to Step 4 | Go to Step 5 | |
|
Important: Continuously excessive fan noise is due to the PCM commanding the cooling fan clutch to 100% engaged or a mechanical failure. If the fan noise decreases during this step, then this DTC is due to an electrical malfunction. Replacing the cooling fan clutch will not correct the condition.
Does the cooling fan clutch disengage? | -- | Go to Step 5 | Go to Step 18 | |
Does the Fan Speed parameter increase? | -- | Go to Diagnostic Aids | Go to Step 6 | |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 11 | |
7 | Test the cooling fan clutch control circuit of the cooling fan relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 8 |
8 | Test the cooling fan clutch control circuit of the cooling fan relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 9 |
9 |
Is the frequency less than the specified value? | OL | Go to Step 14 | Go to Step 10 |
10 | Command the Fan Control to 100%. Does the frequency fluctuate? | -- | Go to Step 13 | Go to Step 14 |
11 | Inspect the Eng Fan fuse. Is the fuse open? | -- | Go to Step 12 | Go to Step 15 |
12 | Test the cooling fan clutch control circuit of the cooling fan relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15 |
13 | Inspect for poor connections at the cooling fan relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
14 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 |
15 | Repair the ignition 1 voltage circuit of the cooling fan relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
16 | Replace the cooling fan relay. Did you complete the replacement? | -- | Go to Step 19 | -- |
17 |
Important: Perform the programming procedure for the PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls-4.8L, 5.3L, and 6.0L. Did you complete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the cooling fan clutch. Refer to Fan Clutch Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
