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

Circuit Description

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

Battery positive voltage is supplied to the S/P relay and the cooling fan 2 relay from the COOL 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.

    • Cooling fan relay 1 control circuit refers to the low speed fan circuit.
    • Cooling fan relay 2 control circuit refers to the high speed fan circuit.

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 is ON.
    • System voltage is between 9-18 volts.
    • The relay control circuit is transitioned from OFF to ON or ON to OFF.

Conditions for Setting the DTC
    • An improper voltage level has been detected on the cooling fan relay control circuit.
    • The above conditions are 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 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 .
    • 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 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 S/P relay and cooling fan 2 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.

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

2

  1. Install a scan tool.
  2. Start the engine.
  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 S/P and the cooling fan 2 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 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 16

5

  1. Connect a test lamp between the control circuit of the cooling fan 1 relay 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 12

Go to Step 9

6

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan 2 relay.
  3. Turn ON the ignition, with the engine OFF.
  4. 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 16

7
  1. 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.
  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 S/P relay.
  3. Turn ON the ignition with the engine OFF.
  4. Connect a test lamp between the control circuit of the S/P relay and the battery positive voltage circuit of the S/P 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 .

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 .

Did you find and correct the condition?

Go to Step 21

Go to Step 15

12

Inspect for poor connections at the cooling fan 1 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 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 cooling fan 2 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 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 .

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 .

Did you complete the repair?

Go to Step 21

--

17

Replace the cooling fan 1 relay.

Did you complete the replacement?

Go to Step 21

--

18

Replace the S/P relay.

Did you complete the replacement?

Go to Step 21

--

19

Replace the cooling fan 2 relay.

Did you complete the replacement?

Go to Step 21

--

20

Replace the PCM. Refer to Control Module References 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