Hummer H3. Manual — part 1308

1. Perform the Brake System Vehicle Road Test before using the hydraulic brake symptom

tables in order to duplicate the customer's concern.

2. Review the system operation in order to familiarize yourself with the system functions.

Refer to the following procedures:

Brake Warning System Description and Operation

Hydraulic Brake System Description and Operation

Brake Assist System Description and Operation

Disc Brake System Description and Operation

Visual/Physical Inspection

Inspect for aftermarket devices which could affect the operation of the Hydraulic Brake
System. Refer to Checking Aftermarket Accessories .

Inspect the easily accessible or visible system components for obvious damage or conditions
which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the
symptom:

Brake Warning Indicator Malfunction

Brake Pulsation

Brake System Noise

Braking Action Uneven - Pulls to One Side

Braking Action Uneven - Front to Rear

Brake Pedal Excessive Travel

Brake Pedal Excessive Effort

Brakes Drag

Brake System Slow Release

tables.

2007 Hummer H3

2007 BRAKES Hydraulic Brakes - H3

Brake Fluid Loss

BRAKE WARNING INDICATOR MALFUNCTION

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The electronic brake control module (EBCM) monitors the brake fluid level switch via the brake
fluid level sensor signal circuit. With the switch closed, the signal circuit is pulled to ground
indicating low fluid level. When low fluid level is seen, a serial data message is sent to the
instrument panel cluster (IPC) to illuminate the red brake warning indicator. The body control
module (BCM) monitors the park brake switch via the park brake switch signal circuit. With the
park brake applied, the switch is closed and the signal circuit is grounded. The BCM will then
send a serial data message to the IPC requesting the red brake warning indicator be illuminated.

Reference Information

Schematic Reference

Hydraulic Brake Schematics

Connector End View Reference

Hydraulic Brake Connector End Views

Description and Operation

Brake Warning System Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

2007 Hummer H3

2007 BRAKES Hydraulic Brakes - H3

Circuit/System Verification

1. Verify the park brake is released and the brake fluid is at the proper level.

If the brake fluid is not at the proper level, refer to Brake Fluid Loss.

2. Ignition ON, perform the scan tool IPC Display Test. The red brake warning indicator

should illuminate.

If the red brake warning indicator does not illuminate, replace the IPC.

3. Observe the scan tool BCM Park Brake Switch parameter while applying and releasing the

park brake. The parameter should cycle between Applied and Release.

If the parameter does not cycle between the specified values, refer to Park Brake
Switch Circuit Malfunction in Circuit/System Testing.

4. Verify the scan tool EBCM Brake Fluid parameter is OK.

If not the specified value, refer to Brake Fluid Level Switch Circuit Malfunction in
Circuit/System Testing.

Circuit/System Testing

Park Brake Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the park brake switch.

2. Ignition ON, verify the scan tool BCM Park Brake Switch parameter is Released.

If not the specified value, test the signal circuit terminal A for a short to ground. If the
circuit tests normal, replace the BCM.

3. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the

scan tool BCM Park Brake Switch parameter is Applied.

If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance.

4. If all circuits test normal, test or replace the park brake switch.

Brake Fluid Level Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the brake fluid level switch.

2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal 1

and ground.

If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool EBCM Brake Fluid parameter is OK.

If not the specified value, test the signal circuit terminal 2 for a short to ground. If the

2007 Hummer H3

2007 BRAKES Hydraulic Brakes - H3

circuit tests normal, replace the EBCM.

4. Install a 3A fused jumper wire between the signal circuit terminal 2 and the ground circuit

terminal 1. Verify the scan tool EBCM Brake Fluid parameter is Low.

If not the specified value, test the signal circuit for a short to voltage or an open/high
resistance. If the circuit tests normal, replace the EBCM.

5. If all the circuits test normal, test or replace the brake fluid level switch.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Parking Brake Indicator Switch Replacement (LHD) or Parking Brake Indicator
Switch Replacement (RHD)

Control Module References for BCM, EBCM and IPC replacement, setup and
programming

BRAKE PULSATION

Brake Pulsation

Step

Action

Yes

No

DEFINITION: Fluctuation or pulsation is felt through the brake pedal, steering wheel, seat,
floor, and/or in the vehicle ONLY when braking.

1

Were you sent here from the Hydraulic
Brake Symptom table?

Go to Step 2

Go to
Diagnostic
Starting Point -
Hydraulic
Brakes

1. Inspect the disc brake system for the

following conditions.

Excessive thickness variation of
rotor friction surfaces

Excessive assembled lateral
runout (LRO) of rotor friction
surfaces

Hard spots, heat checks, bluing
discoloration of rotor friction
surfaces; possibly due to brake
drag

2007 Hummer H3

2007 BRAKES Hydraulic Brakes - H3