For 1990-2009 cars

## Park Brake Pump Motor Does Not Run w/o MUQ

### 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. Illumination of the LED on PBCM indicates the PBCM is attempting to energize the park brake pump motor relay.

2. The PBCM may be damaged if the park brake motor relay control circuit is shorted to ground.

Step | Action | 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 |

1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
2. Ensure the parking brake is applied.
3. Turn ON the ignition.
4. Release the parking brake.

Does the parking brake pump motor run?

Go to Diagnostic Aids

Go to Step 3

3 | Observe the LED on the side of the PBCM. Does the LED illuminate? | Go to Step 4 | Go to Step 15
4 |

1. Disconnect the parking brake pump motor harness connector.
2. Connect a test lamp between the park brake pump motor supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

5 | Test the ground circuit of the park brake pump motor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 29 | Go to Step 13
6 |

1. Disconnect the park brake pump motor relay harness connector.
2. Test the park brake pump motor supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 7

7 | Connect a test lamp between the battery positive voltage circuit at the park brake pump motor relay harness connector and a good ground. Does the test lamp illuminate? | Go to Step 8 | Go to Step 22
8 | Connect a test lamp between the park brake pump motor relay control circuit, at the park brake pump motor relay harness connector, and a good ground. Does the test lamp illuminate? | Go to Step 10 | Go to Step 9
9 |

1. Turn OFF the ignition.
2. Disconnect from the PBCM, the harness connector containing the park brake motor relay control circuit.
3. Test the park brake motor relay control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 25

10 |

1. Reconnect the PBCM harness connector.
2. Test the ground circuit of the park brake pump motor relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 11

11 | Inspect for poor connections at the harness connector of the park brake pump motor relay. 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 29 | Go to Step 12
12 | Replace the park brake pump motor relay. Refer to Park Brake Pump Relay Replacement . Did you complete the replacement? | Go to Step 29 | --
13 | Inspect for poor connections at the harness connector of the park brake pump motor. 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 29 | Go to Step 14
14 | Replace the park brake pump motor. Refer to Park Brake Pump Replacement . Did you complete the replacement? | Go to Step 29 | --
15 |

1. Turn OFF the ignition.
2. Disconnect from the PBCM, the harness connector containing the park brake pressure valve solenoid supply voltage circuit.
3. Turn ON the ignition.
4. Connect a test lamp between the park brake pressure valve solenoid supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 25

Go to Step 16

16 | Test the park brake pressure valve solenoid supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 29 | Go to Step 17
17 | Important: For vehicles not equipped with a park brake relay, proceed to Step 19 . Connect a test lamp between the battery positive voltage circuit, at the park brake relay harness connector, and a good ground. Does the test lamp illuminate? | Go to Step 18 | Go to Step 22
18 | Connect a test lamp between the park brake relay control circuit, at the park brake relay harness connector, and a good ground. Does the test lamp illuminate? | Go to Step 21 | Go to Step 19
19 |

1. Disconnect the park brake switch harness connector.
2. Connect a test lamp between the battery positive voltage circuit, at the park brake switch harness connector, and a good ground.

Does the test lamp illuminate?

Go to Step 20

Go to Step 22

20 | Important: For vehicles not equipped with a park brake relay, proceed to Step 27 . Test the park brake relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 29 | Go to Step 27
21 | Test the ground circuit of the park brake relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 29 | Go to Step 23
22 | Repair the open in the battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 29 | --
23 | Inspect for poor connections at the harness connector of the park brake relay. 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 29 | Go to Step 24
24 | Replace the park brake relay. Refer to Park Brake Relay Replacement . Did you complete the replacement? | Go to Step 29 | --
25 | 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 29 | Go to Step 26
26 | Replace the PBCM. Refer to Park Brake Control Module Replacement . Did you complete the replacement? | Go to Step 29 | --
27 | Inspect for poor connections at the harness connector of the park brake 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 29 | Go to Step 28
28 | Replace the park brake switch. Refer to Instrument Panel Park Brake Switch Replacement . Did you complete the replacement? | Go to Step 29 | --
29 |

1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
2. Ensure the parking brake is applied.
3. Turn ON the ignition.
4. Release the parking brake.

Does the parking brake pump motor run?

System OK

Go to Step 3

## Park Brake Pump Motor Does Not Run w/ MUQ

### 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 gear selector must be placed in any gear other than park or neutral in order for the PBCM to command the parking brake to release. Place the gear selector in reverse or drive with the wheels blocked for the duration of this diagnostic procedure.

2. Illumination of the LED on PBCM indicates the PBCM is attempting to energize the park brake pump motor relay.

3. The PBCM may be damaged if the park brake pump motor relay control circuit is shorted to ground.

4. This step ensures the PBCM is receiving a voltage signal requesting the parking brake be released.

5. This step tests for a shorted PNP switch.

6. A shorted transmission shift select switch signal circuit sends a signal to the PBCM indicating the gear selector is always in park or neutral.

Step | Action | 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 |

1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
2. Ensure the parking brake is applied.
3. Turn ON the ignition, with the engine OFF.
4. Place the gear selector in reverse or drive.

Does the parking brake pump motor run?

Go to Diagnostic Aids

Go to Step 3

3 | Observe the LED on the side of the PBCM. Does the LED illuminate? | Go to Step 4 | Go to Step 15
4 |

1. Disconnect the parking brake pump motor harness connector.
2. Connect a test lamp between the park brake pump motor supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

5 | Test the ground circuit of the park brake pump motor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 33 | Go to Step 13
6 |

1. Disconnect the park brake pump motor relay harness connector.
2. Test the park brake pump motor supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 7

7 | Connect a test lamp between the battery positive voltage circuit (at the park brake pump motor relay harness connector) and a good ground. Does the test lamp illuminate? | Go to Step 8 | Go to Step 32
8 | Connect a test lamp between the park brake pump motor relay control circuit (at the park brake pump motor relay harness connector) and a good ground. Does the test lamp illuminate? | Go to Step 10 | Go to Step 9
9 |

1. Turn OFF the ignition.
2. Disconnect from the PBCM, the harness connector containing the park brake pump motor relay control circuit.
3. Test the park brake pump motor relay control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 29

10 |

1. Reconnect the PBCM harness connector.
2. Test the ground circuit of the park brake pump motor relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 33

Go to Step 11

11 | Inspect for poor connections at the harness connector of the park brake pump motor relay. 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 33 | Go to Step 12
12 | Replace the park brake pump motor relay. Refer to Park Brake Pump Relay Replacement . Did you complete the replacement? | Go to Step 33 | --
13 | Inspect for poor connections at the harness connector of the park brake pump motor. 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 33 | Go to Step 14
14 | Replace the park brake pump motor. Refer to Park Brake Pump Replacement . Did you complete the replacement? | Go to Step 33 | --
15 |

1. Turn OFF the ignition.
2. Disconnect from the PBCM, the harness connector containing the park brake pressure valve solenoid supply voltage circuit.
3. Turn ON the ignition.
4. Connect a test lamp between the park brake pressure valve solenoid supply voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 29

Go to Step 16

16 |

1. Disconnect the park brake switch harness connector.
2. Connect a test lamp between the park brake switch supply voltage circuit (at the park brake switch harness connector) and a good ground.

Does the test lamp illuminate?

Go to Step 17

Go to Step 18

17 | Test the park brake pressure valve solenoid supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 33 | Go to Step 28
18 |

1. Turn ON the ignition.
2. Disconnect the park/neutral position (PNP) switch harness connector.

Does the pump motor run?

Go to Step 20

Go to Step 19

19 | Test the transmission shift select switch 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 33 | Go to Step 21
20 | Adjust or replace the PNP switch. Refer to Park/Neutral Backup Switch Adjustment or Park/Neutral Backup Switch Replacement in Automatic Transmission - Allison. Did you complete the repair? | Go to Step 33 | --
21 |

1. Turn ON the ignition.
2. Disconnect the column shift relay.
3. Connect a test lamp between battery positive voltage and the control circuit of the relay coil.

Does the test lamp illuminate?

Go to Step 23

Go to Step 22

22 | Test the column shift relay control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 33 | Go to Step 29
23 | Use a test lamp connected to ground in order to verify power at the ignition 1 circuit and at the battery positive voltage circuit of the column shift relay. Does the test lamp illuminate when connected to each circuit, one at a time? | Go to Step 25 | Go to Step 24
24 | Repair the open in the circuit which did not illuminate the test lamp. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 33 | --
25 | Test the park brake switch supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 33 | Go to Step 26
26 | Inspect for poor connections at the connector of the column shift relay. 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 33 | Go to Step 27
27 | Replace the column shift relay. Did you complete the replacement? | Go to Step 33 | --
28 | Inspect for poor connections at the harness connector of the park brake 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 33 | Go to Step 31
29 | 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 33 | Go to Step 30
30 | Replace the PBCM. Refer to Park Brake Control Module Replacement . Did you complete the replacement? | Go to Step 33 | --
31 | Replace the park brake switch. Refer to Instrument Panel Park Brake Switch Replacement . Did you complete the replacement? | Go to Step 33 | --
32 | Repair the open in the battery positive voltage circuit. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you complete the repair? | Go to Step 33 | --
33 |

1. Block the drive wheels in order to ensure the vehicle does not roll when the parking brake is released.
2. Ensure the parking brake is applied.
3. Turn ON the ignition, with the engine OFF.
4. Place the gear selector in reverse or drive.

Does the parking brake pump motor run?

System OK

Go to Step 3