Circuit Description
The powertrain control module (PCM) controls the low speed cooling fan operation by grounding the low speed fan relay control circuit with an internal solid state device called a driver. For high speed cooling fan operation, the PCM grounds the high speed and S/P relay control circuit at the same time the low speed control circuit is grounded. Battery positive voltage is supplied to the low speed, high speed and S/P fan relays. When the PCM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the PCM is commanding a fan relay OFF, the voltage potential of the control circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the DTC will set.
If the PCM detects an improper voltage level on the low or high speed driver circuits, then code P0480 or P0481 will set and the effected driver will be disabled.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0480 Cooling Fan Relay 1 Control Circuit |
| • | DTC P0481 Cooling Fan Relay 2 and 3 Control Circuit |
Conditions for Running the DTC
| • | The ignition voltage is between 9.0-18.0 volts. |
| • | The engine speed is more than 40 RPM. |
| • | The PCM driver transitions from ON to OFF or from OFF to ON. |
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 records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The PCM stores the DTC information into memory when the diagnostic runs and fails. |
| • | The driver information center if equipped, may display a message. |
Conditions for Clearing the MIL/DTC
| • | The PCM 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. |
| • | Use the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Review the Freeze/Failure Records vehicle mileage since the diagnostic test failed. This may help determine how often the condition that caused the DTC to be set occurs. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Listen for an audible click when the cool fan relay 1 operates. Command both the ON and OFF states. Repeat the commands as necessary.
-
Listen for an audible click when the S/P and cool fan 2 relays operate. 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 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Does the cool fan 1 relay turn ON and OFF with each command? | Go to Step 3 | Go to Step 4 | |
With a scan tool, command the Fans High Speed ON and OFF. Do the S/P and the cool fan 2 relays turn ON and OFF with each command? | Go to Diagnostic Aids | Go to Step 6 | |
4 |
Does the test lamp illuminate? | Go to Step 5 | Go to Step 16 |
5 |
Does the test lamp turn ON and OFF with each command? | Go to Step 12 | Go to Step 9 |
6 |
Does the test lamp illuminate? | Go to Step 7 | Go to Step 16 |
7 |
Does the test lamp turn ON and OFF with each command? | Go to Step 14 | Go to Step 8 |
8 |
Does the test lamp turn ON and OFF with each command? | Go to Step 13 | Go to Step 9 |
9 | Does the test lamp remain illuminated with each command? | Go to Step 11 | Go to Step 10 |
10 | Test the control circuit of the appropriate relay for a short to voltage or an open. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 15 |
11 | Test the control circuit of the appropriate relay for a short to ground. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 15 |
12 | Inspect for poor connections at the cool fan 1 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 21 | Go to Step 17 |
13 | Inspect for poor connections at the S/P 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 21 | Go to Step 18 |
14 | Inspect for poor connections at the cool fan 2 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 21 | Go to Step 19 |
15 | Inspect for poor connections at the harness connector of the powertrain control module (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 21 | Go to Step 20 |
16 | Repair the battery voltage circuit for an open or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 21 | -- |
17 | Replace the cool fan 1 relay. Did you complete the repair? | Go to Step 21 | -- |
18 | Replace the S/P fan relay. Did you complete the repair? | Go to Step 21 | -- |
19 | Replace the cool fan 2 relay. Did you complete the repair? | Go to Step 21 | -- |
20 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming. Did you complete the replacement? | Go to Step 21 | -- |
21 |
Does the DTC reset? | Go to Step 2 | System OK |
