GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 Yukon XL - 2WD 🢒 Engine 🢒 Engine Cooling 🢒 DTC P0480 or P0481

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.

The PCM monitors the relay control circuits for the following conditions:

    • Short to ground
    • Short to voltage
    • An open circuit

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.

    • 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 PCM detects an open circuit on the high speed cooling fan relay control circuit.
    • P0480--The PCM detects an open on the low speed cooling fan relay control circuit.
    • The above condition is present for one second.

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.
    • 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 .
    • Review the Freeze Frame/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.

  1. Listen for an audible click when the low speed fan 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 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

Go to Diagnostic System Check - Vehicle

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 low speed fan 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 high speed fan 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 low speed fan relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit of the low speed fan 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 low speed fan relay and the ignition 3 voltage circuit of the low speed fan 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 high speed fan relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit of the high speed fan 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 high speed fan relay and the ignition 3 voltage circuit of the high speed fan 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 fan relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the control circuit of the S/P fan relay and the ignition 3 voltage circuit of the S/P fan 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 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 .

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 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 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