Circuit Description
The engine control module (ECM) 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 ECM 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 ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage potential of the control circuit should be high, near battery voltage.
The ECM monitors the relay control circuits for the following conditions:
| • | Short to ground |
| • | Short to voltage |
| • | An open circuit |
If the ECM 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.
| • | Cooling fan relay 1 control circuit refers to the low speed cooling fan relay |
| • | Cooling fan relay 2 control circuit refers to the high speed cooling fan relay |
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0480 Cooling Fan Relay 1 Control Circuit |
| • | DTC P0481 Cooling Fan Relay 2 Control Circuit |
Conditions for Running the DTC
| • | The ignition voltage is between 8-18 volts. |
| • | The engine speed is more than 40 RPM. |
| • | The ECM driver transitions from ON to OFF or from OFF to ON. |
Conditions for Setting the DTC
P0481
The ECM detects an open circuit on the high speed cooling fan relay control circuit.
P0480
The ECM detects an open on the low speed cooling fan relay control circuit.
The above condition is present for 1 second.
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 conditions which 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. |
| • | Use the scan tool Clear DTC Information function. |
Diagnostic Aids
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 low speed fan relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
-
Listen for an audible click when the S/P and high speed fan 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 | |
Does the low speed fan 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 high speed fan 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 . 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 . Did you find and correct the condition? | Go to Step 21 | Go to Step 15 |
12 | Inspect for poor connections at the low speed fan relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . 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 . Did you find and correct the condition? | Go to Step 21 | Go to Step 18 |
14 | Inspect for poor connections at the high speed 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 19 |
15 | 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 21 | Go to Step 20 |
16 | Repair the ignition 3 voltage circuit for an open or high resistance. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 21 | -- |
17 | Replace the low speed fan 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 high speed fan relay. Did you complete the repair? | Go to Step 21 | -- |
20 | Replace the ECM. Refer to Control Module References 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 |
