GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC Sierra Denali 🢒 DTC 🢒 DTC C0481

Circuit Description

The electro-hydraulic power steering (EHPS) operates when voltage at the EHPS connector is in the range of 34-50 volts. The EHPS will go into standby mode if the supply voltage at the EHPS connector drops below 18 volts for more than 10 milliseconds. The EHPS module shall be turned back on once the supply voltage rises above 22 volts, without a key cycle being required. If the supply voltage drops below 12 volts, the EHPS module drivers shall shut down and a key cycle will be required to reset. The EHPS module shall withstand voltages up to a transient voltage of 58 volts for 400 milliseconds. If the supply voltage exceeds 55 volts, the EHPS module drives shall shut down and a key cycle will be required to reset. The 36 volts power supply is grounded directly to the negative terminal of the EHPS.

Conditions for Running the DTC
    • EHPS module in RUN mode.
    • Ignition switch in ACC or ON position.
    • Battery voltage between 12-58 volts.

Conditions for Setting the DTC

The EHPS module commands the electric motor to operate at a set speed, but the output sensed by the hall-effect sensor is equal to zero.

Action Taken When the DTC Sets
    • System operation is reduced.
    • The SERVICE BRAKE SYSTEM message and SERVICE STEER SYSTEM message will be displayed.
    • A chime will sound.
    • EHPS module operation is normal, but the electric motor control is inactive.
    • Stores DTC C0481 in the powertrain control module (PCM).
    • History DTC C0481 will be set in PCM.

Conditions for Clearing the DTC
    • EHPS module can detect the proper motor RPM.
    • Using the scan tool.
    • A history DTC will clear after 255 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

It may be necessary to check Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. This step checks for 2,500 RPM that was set with the scan tool.

    2.

  2. This step checks for motor current at 2,500 RPM.

    3.

  3. This step checks for the EHPS demand parameter percentage.

    4.

  4. This step checks if the motor speed is more than 2,500 RPM.

    5.

  5. This step checks if the motor speed is steady.

    6.

  6. This step checks for the EHPS demand parameter percentage.

    7.

  7. This step checks for motor current.

Step

Action

Value(s)

Yes

No

Schematic Reference: Power Steering Schematics

Connector End Views Reference: Power Steering Connector End Views

1

Did you perform the electro-hydraulic power steering (EHPS) Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Power Steering System

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine ON.
  3. With a scan tool, set the EHPS Demand Speed to 2,500 RPM.
  4. Observe the EHPS Motor RPM parameter on the scan tool data list.

Does the EHPS Motor RPM parameter value match what was set?

2,500 RPM

Go to Step 3

Go to Step 5

3

With a scan tool, observe the EHPS Motor Current parameter on the data list.

Is the Motor Current parameter less than the specified value?

15 A

Go to Step 4

Go to Step 11

4

With a scan tool, observe the EHPS Demand parameter on the data list.

Is the EHPS Demand parameter less than the specified value?

50 percent

Go to Diagnostic Aids

Go to Step 11

5

With a scan tool, observe the EHPS Motor RPM parameter on the data list.

Is the EHPS Motor RPM parameter greater than the specified value?

2,500 RPM

Go to Step 6

Go to Step 7

6

With a scan tool, observe the EHPS Motor RPM parameter value on the data list.

Is the motor speed steady?

--

Go to Step 10

Go to Step 9

7

With a scan tool, observe the EHPS Demand parameter value on the data list.

Is the EHPS Demand parameter greater than the specified value?

50 percent

Go to Step 8

Go to Step 9

8

With a scan tool, observe the EHPS Motor Current parameter value on the data list.

Is the EHPS Motor Current parameter greater than the specified value?

15 A

Go to Step 11

Go to Step 12

9
  1. Reload the calibration. Refer to Service Programming System (SPS) in Programming.
  2. Use the scan tool to perform the Pump Motor Test function in Scan Tool Output Controls to reset motor RPM.

Have the procedures been completed?

--

Go to Step 13

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10

Reprogram the EHPS module. Refer to Service Programming System (SPS) in Programming.

Has procedure been completed?

--

Go to Step 13

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11

Repair hydraulic system.

Did you complete hydraulic system repair?

--

Go to Step 13

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12

Important: Always perform the calibration procedure for the brake pedal position (BPP) sensor. Refer to Brake Pedal Position Sensor Calibration Description and Operation .

Replace the EHPS powerpack. Refer to Power Steering Pump Replacement .

Has the replacement been completed?

--

Go to Step 13

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13
  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