GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2004 🢒 Regal 🢒 DTC 🢒 DTC P0480 or P0481

Circuit Description

The following DTC's are for the cooling fan relay control circuits controlled by the powertrain control module (PCM).

    • P0480 - low speed cooling fan relay control circuit
    • P0481 - high speed cooling fan relay control circuit

Battery positive voltage is supplied to the cool fan 1 relay from the cool fan 1 fuse. The PCM controls the low speed cooling fan relay by grounding the low speed cooling fan relay control circuit.

Battery positive voltage is supplied to the cool fan 2 relay and the cool fan 3 relay from the cool fan 2 fuse. The PCM controls the high speed cooling fan relays by grounding the high speed cooling fan relay control circuit.

The PCM 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 PCM. When the PCM is commanding a component on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM 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 PCM 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 PCM detects any of the above conditions, the DTC will set and the effected driver will be disabled.

Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is between 9.0 and 18.0 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 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 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 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.
    • 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 in Wiring Systems.
    • 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.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the cooling fan 1 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Listen for an audible click when the cooling fan 2 and the cooling fan 3 relays operate. Command both the ON and OFF states. Repeat the commands as necessary.

    3.

  3. Tests for voltage at the coil side of the cooling fan 1 relay. The cool fan 1 fuse supplies battery positive voltage to the coil side of the cooling fan  1 relay.

    4.

  4. Verifies that the PCM is providing ground to the cooling fan 1 relay.

    5.

  5. Tests for voltage at the coil side of the cooling fan 2 relay. The cool fan 2 fuse supplies battery positive voltage to the coil side of the cooling fan 2 and cooling fan 3 relays.

    6.

  6. Verifies that the PCM is providing ground to the cooling fan 2 relay.

    7.

  7. Verifies that the PCM is providing ground to the cooling fan 3 relay.

    8.

  8. Tests if ground is constantly being applied to the cooling fan relays.

    9.

  9. Test the control circuit of the cooling fan relays for a short to voltage or an open.

    10.

  10. Test the control circuit of the cooling fan relays for a short to ground.

    11.

  11. Test the battery positive voltage circuit for a short to ground.

Step

Action

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

Go to Diagnostic System Check - Engine Cooling

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the Fans Low Speed ON and OFF.

Does the cooling fan 1 relay turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3

With a scan tool, command the Fans High Speed ON and OFF.

Do the cooling fan 2 and the cooling fan 3 relays turn ON and OFF with each command?

Go to Diagnostics Aids

Go to Step 6

4

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan 1 relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the battery positive voltage circuit of the cooling fan 1 relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 12

5

  1. Connect a test lamp between the low-speed cooling fan relay control circuit and the battery positive voltage circuit of the cooling fan 1 relay.
  2. With a scan tool, command the Fans Low Speed ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 13

Go to Step 9

6

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan 2 relay.
  3. Probe the battery positive voltage circuit of the cooling fan 2 relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 12

7

  1. Turn ON the ignition.
  2. Connect a test lamp between the control circuit of the cooling fan 2 relay and the battery positive voltage circuit of the cooling fan 2 relay.
  3. With a scan tool, command the Fans High Speed ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 15

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan 3 relay.
  3. Turn ON the ignition with the engine OFF.
  4. Connect a test lamp between the control circuit of the cooling fan 3 relay and the battery positive voltage circuit of the cooling fan 3 relay.
  5. With a scan tool, command the Fans High Speed ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 14

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 Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 22

Go to Step 16

11

Test the control circuit of the appropriate 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 22

Go to Step 16

12

Test the battery positive voltage circuit for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 22

Go to Step 17

13

Inspect for poor connections at the cooling 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 22

Go to Step 18

14

Inspect for poor connections at the cooling fan 3 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 22

Go to Step 19

15

Inspect for poor connections at the cooling 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 22

Go to Step 20

16

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.

Go to Step 22

Go to Step 21

17

Repair the cooling fan motor supply voltage circuit for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 22

--

18

Replace the cooling fan 1 relay.

Did you complete the replacement?

Go to Step 22

--

19

Replace the cooling fan 3 relay.

Did you complete the replacement?

Go to Step 22

--

20

Replace the cooling fan 2 relay.

Did you complete the replacement?

Go to Step 22

--

21

Important: Perform the programming procedure for the PCM.

Replace the PCM. Refer to Powertrain Control Module Replacement -- 3.1L or Powertrain Control Module Replacement -- 3.8L in Engine Controls.

Did you complete the replacement?

Go to Step 22

--

22
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK