GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Yukon - 2WD 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0282, C0285, or C0286

Circuit Description

The brake pressure modulator valve (BPMV) contains a medium pressure accumulator (MPA). The MPA provides pressure to the front brakes during certain VSES events. The MPA switch is included to monitor the status of the pressure accumulator. The MPA switch is open when the MPA is uncharged.

The integrity of the MPA switch is tested by the EBCM. The MPA is partially discharged during system initialization to open the switch, and then recharged to close the switch. The EBCM continues to monitor the switch to ensure the MPA remains charged. Provided the VSES is not activated, the MPA should remain charged for the entire ignition cycle. If the MPA switch opens within 5 minutes of closing, a fast leakdown condition is detected. If the MPA switch opens after 5 minutes has passed, a slow leakdown condition is detected.

Conditions for Running the DTC

C0282 and C0285

    • The ignition is ON.
    • The vehicle speed is greater than 12 km/h (8 mph).

C0286

    • The ignition is ON.
    • The MPA switch is closed.
    • The diagnostic tests for DTC C0282 and C0285 have ran and passed.

Conditions for Setting the DTC

C0282

The MPA switch remains closed when the MPA is discharged for 1-2 seconds, depending on ambient temperature.

C0285

During the MPA charging period, the MPA switch does not close within the time indicated on the following table.

Ambient Temperature

Fault Timer

Greater than 0°C (32°F)

86 sec

Between -30°C and 0°C

(-22°F and 32°F)

170 sec

Less than -30°C (-22°F)

230 sec

C0286

Any of the following conditions may cause DTC C0286 to set.

    • The EBCM detects 2 fast MPA leakdowns during the system initialization period.
    • The EBCM detects 3 fast MPA leakdowns after the system has initialized.
    • The sum of the fast and slow MPA leakdowns detected after the system has initialized equals 7.

Action Taken When the DTC Sets
    • The EBCM disables the VSES.
    • The message center displays the SERVICE STABILITY SYSTEM message.

Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs function.

Diagnostic Aids

Thoroughly inspect the MPA switch jumper harness for any condition that may cause an intermittent malfunction. Refer to Testing for Electrical Intermittents , Testing for Intermittent Conditions and Poor Connections , Wiring Repairs and Connector Repairs in Wiring Systems.

An intermittent DTC may be difficult to verify since the DTC may take a substantial amount of time to set. If a DTC continues to set intermittently, remove the MPA switch and activate the switch by pressing and releasing the plunger. Ensure the plunger movement is smooth and that the plunger releases readily without sticking. Observe the MPA Switch input on the scan tool to verify that the status changes from Uncharged to Charged every time the switch is pressed. Replace the BPMV if no fault is found in the switch, circuitry or connections. Refer to Brake Pressure Modulator Valve Replacement .

Test Description

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

  1. This step simulates an open MPA switch.

    2.

  2. This step simulates a closed MPA switch.

    3.

  3. This step tests the MPA switch by closing the switch manually.

    4.

  4. This step tests the MPA switch by ensuring the switch plunger is in the open position.

Step

Action

Yes

No

Schematic Reference: Antilock Brake System Schematics

Important: The introduction of air into the brakes' hydraulic system due to a BPMV replacement or for any other reason may cause DTC C0285 or C0286 to set. If it suspected that air may have been introduced to the hydraulic system, use the scan tool to perform the VSES Automated Bleed procedure and the Bleed MPA procedure before proceeding with this diagnostic table. You must refer to Antilock Brake System Automated Bleed Procedure for complete system bleeding instructions.

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - ABS

2
  1. Use a 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 for 10 minutes or until the DTC resets.

Does the DTC reset?

Go to Step 3

Go to Diagnostic Aids

3
  1. Turn ON the ignition.
  2. Select the VSES Data List on the scan tool.
  3. Observe the MPA Switch input on the scan tool.

Does the scan tool display Charged?

Go to Step 4

Go to Step 5

4

  1. Turn OFF the ignition.
  2. Disconnect the MPA switch harness connector.
  3. Turn ON the ignition.
  4. Observe the MPA Switch input on the scan tool.

Does the scan tool display Uncharged?

Go to Step 7

Go to Step 9

5

  1. Turn OFF the ignition.
  2. Disconnect the MPA switch harness connector.
  3. Use a fused jumper wire to connect the MPA switch supply circuit to the MPA switch signal circuit. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Turn ON the ignition.
  5. Observe the MPA Switch input on the scan tool.

Does the scan tool display Charged?

Go to Step 6

Go to Step 8

6

  1. Remove the MPA switch from the BPMV. Refer to Pressure Accumulator Switch Replacement .
  2. Reconnect the MPA switch harness connector.
  3. Press and hold the MPA switch plunger.
  4. Observe the MPA Switch input on the scan tool.

Does the scan tool display Charged?

Go to Step 15

Go to Step 12

7

  1. Remove the MPA switch from the BPMV. Refer to Pressure Accumulator Switch Replacement .
  2. Reconnect the MPA switch harness connector.
  3. Observe the MPA Switch input on the scan tool.

Does the scan tool display Uncharged?

Go to Step 15

Go to Step 14

8

Test the MPA switch supply circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 10

9

Test the MPA switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 13

10

Test the MPA switch signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 11

11

Inspect for poor connections at the harness connector of the EBCM. 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 16

Go to Step 13

12

Inspect for poor connections at the harness connector of the MPA switch. 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 16

Go to Step 14

13

Important: Following EBCM replacement, use the scan tool to perform the Tire Size Calibration procedure.

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Did you complete the replacement?

Go to Step 16

--

14

Replace the MPA switch. Refer to Pressure Accumulator Switch Replacement .

Did you complete the replacement?

Go to Step 16

--

15

Important: DTC C0285 or C0286 may set after BPMV replacement if the VSES Automated Bleed procedure and the Bleed MPA Procedure are not performed exactly as specified in the service manual instructions. Refer to Antilock Brake System Automated Bleed Procedure (w/JL4) for complete bleed instructions.

Replace the BPMV. Refer to Brake Pressure Modulator Valve Replacement .

Did you complete the replacement?

Go to Step 16

--

16
  1. Use a 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 for 10 minutes or until the DTC resets.

Does the DTC reset?

Go to Step 3

System OK