GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2001 🢒 Isuzu T-Series (Truck Line C) 🢒 Brakes 🢒 Park Brake 🢒 Park Brake Pressure Sensor Circuit Check

Circuit Description

In order to release the parking brake, the pump motor must supply fluid pressure to the actuator. When this pressure overcomes the spring tension inside of the actuator, the actuator piston moves, releasing the parking brake. The park brake pressure sensor monitors the fluid pressure whenever the ignition is ON.

Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

    •  Testing for Electrical Intermittents
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs
    •  Connector Repairs

Test Description

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

  1. The pressure reading displayed should increase steadily from less than 10 percent with the parking brake applied to near 90 percent with the parking brake released.

    2.

  2. This step tests for the proper operation of the circuit in the high voltage range.

    3.

  3. This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

    4.

  4. This step tests for a short to ground in the parking brake pressure sensor 5-volt reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: Park Brake System Schematics

1

Did you perform the Parking Brake Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Park Brake

2

Caution: Keep the brakes applied at all times in order to prevent unexpected vehicle motion. Personal injury may result if the vehicle moves unexpectedly.

  1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
  2. Turn ON the ignition.
  3. Release the parking brake.
  4. Observe the display on the side of the PBCM.

Does the displayed pressure reading increase at a steady rate the entire time the pump is running?

--

Go to Diagnostic Aids

Go to Step 3

3

  1. Apply the parking brake.
  2. Turn OFF the ignition.
  3. Disconnect the parking brake pressure sensor harness connector.
  4. Turn ON the ignition.
  5. Observe the display on the side of the PBCM.

Is the displayed percentage of system operating pressure greater than the specified value?

90%

Go to Step 4

Go to Step 8

4

  1. Turn OFF the ignition.
  2. Connect a 3 amp fused jumper wire between the parking brake pressure sensor signal circuit and the parking brake pressure sensor low reference circuit at the parking brake pressure sensor harness connector.
  3. Turn ON the ignition.
  4. Observe the display on the side of the PBCM.

Is the displayed percentage of system operating pressure less than the specified value?

10%

Go to Step 5

Go to Step 9

5

  1. Turn OFF the ignition.
  2. Disconnect the fused jumper wire.
  3. Connect a 3 amp fused jumper wire between the parking brake pressure sensor 5-volt reference circuit and the parking brake pressure sensor signal circuit .
  4. Turn ON the ignition.
  5. Observe the display on the side of the PBCM.

Is the displayed percentage of system operating pressure greater than the specified value?

90%

Go to Step 7

Go to Step 6

6

Test the parking brake pressure sensor 5-volt reference circuit 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 15

Go to Step 12

7

Test the parking brake pressure sensor 5-volt reference circuit for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

8

Test the parking brake pressure sensor signal circuit 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 15

Go to Step 12

9

Test the parking brake pressure sensor signal circuit for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 10

10

Test the parking brake pressure sensor low reference circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

11

Inspect for poor connections at the harness connector of the parking brake pressure sensor. 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 15

Go to Step 13

12

Inspect for poor connections at the harness connector of the PBCM. 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 15

Go to Step 14

13

Replace the parking brake pressure sensor. Refer to Park Brake Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PBCM. Refer to Park Brake Control Module Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15
  1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
  2. Turn ON the ignition.
  3. Release the parking brake.
  4. Observe the display on the side of the PBCM.

Does the displayed pressure reading increase at a steady rate the entire time the pump is running?

--

System OK

Go to Step 2