GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Grand Prix 🢒 Accessories 🢒 Navigation Systems 🢒 DTC P0480 or P0481

Circuit Description

Battery positive voltage is supplied to the fan 1 relay from the FAN 1 fuse. The powertrain control module (PCM) controls the fan 1 relay by grounding the low speed cooling fan relay control circuit through an internal solid state device called a driver.

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

When the PCM is commanding a relay on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a relay, 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 affected driver will be disabled.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0480 Low Speed Cooling Fan Relay Control Circuit
    • DTC P0481 High Speed Cooling Fan Relay Control Circuit

Conditions for Running the DTC
    • System voltage is between 11-18 volts.
    • The relay control circuit is transitioned ON for at least 0.5 second.

Conditions for Setting the DTC
    • The PCM detects an open or a short to ground on the cooling fan relay control circuit.
    • A short to voltage on the cooling fan relay control circuit will set the DTC instantly.

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 conditions which 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 set occurs.

Test Description

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

  1. Listen for an audible click when the 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 fan 2 and 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 fan 1 relay. The FAN 1 fuse supplies battery positive voltage to the coil side of the fan 1 relay.

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

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

Go to Diagnostic Aids

Go to Step 6

4

  1. Turn OFF the ignition.
  2. Disconnect the fan 1 relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the battery positive voltage circuit of the 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 16

5

  1. Connect a test lamp between the control circuit of the fan 1 relay and the battery positive voltage circuit of the 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 12

Go to Step 9

6

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

Does the test lamp illuminate?

Go to Step 7

Go to Step 16

7
  1. Connect a test lamp between the control circuit of the fan 3 relay and the battery positive voltage circuit of the fan 3 relay.
  2. 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 8

8
  1. Turn Off the ignition.
  2. Disconnect the fan 2 relay.
  3. Turn ON the ignition with the engine OFF.
  4. Connect a test lamp between the control circuit of the fan 2 relay and the battery positive voltage circuit of the fan 2 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 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 Circuit Testing 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 Circuit Testing 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 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 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 18

14

Inspect for poor connections at the 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 21

Go to Step 19

15

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 21

Go to Step 20

16

Repair the battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 21

--

17

Replace the fan 1 relay.

Did you complete the replacement?

Go to Step 21

--

18

Replace the fan 2 relay.

Did you complete the replacement?

Go to Step 21

--

19

Replace the fan 3 relay.

Did you complete the replacement?

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
  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