Hummer H2. Manual - part 774

1. Install the longitudinal accelerometer. 

2. Install the longitudinal accelerometer retaining screws. 

Tighten: Tighten the screws to 2 N.m (18 lb in). 

3. Install I/P bezel. Refer to Trim Panel Replacement - Instrument Panel (I/P) Center in Instrument 

Panel, Gauges and Console.  

DESCRIPTION AND OPERATION 

ABS DESCRIPTION AND OPERATION 

NOTE:

Refer to Fastener Notice in Cautions and Notices.

 

2004 Hummer H2 

2004 BRAKES Anti-Lock Brake System - Hummer H2

  

Fig. 23: BPMV & EBCM 
Courtesy of GENERAL MOTORS CORP. 

Fig. 24: BPMV Hydraulic Flow 
Courtesy of GENERAL MOTORS CORP. 

Callouts For Fig. 24 

Callout

Component Name

1

Master Cylinder

2

Master Cylinder Reservoir

3

Pump

4

Rear Master Cylinder Isolation Valve

5

Rear Prime Valve

6

Brake Pressure Modulator Valve (BPMV)

7

Damper

8

Right Rear Inlet Valve

9

Accumulator

 

2004 Hummer H2 

2004 BRAKES Anti-Lock Brake System - Hummer H2

  

This vehicle is equipped with the Bosch 5.3 anti-lock braking system. 

The vehicle is equipped with the following braking systems: 

z

Anti-lock Brake System (ABS)  

z

Dynamic Rear Proportioning (DRP)  

z

Traction Control System TC2 (w/NW9)  

The following components are involved in the operation of the above systems: 

z

Electronic Brake Control Module (EBCM) - The EBCM controls the system functions and detects 
failures. 

The EBCM contains the following components: 

{

System Relay - The system relay is energized when the ignition is ON and no ABS DTCs are 
present. It supplies battery positive voltage to the solenoid valves and pump motor.  

{

Vent Tube - The vent tube, located in the EBCM connector, is an opening to the internal cavity of 
the EBCM. It allows ventilation of the EBCM internals.  

z

Brake Pressure Modulator Valve (BPMV) - The BPMV contains the hydraulic valves and pump motor 
that are controlled electrically by the EBCM. The vehicle is equipped with traction control The BPMV 
uses a 4 circuit configuration with a front/rear split. The BPMV directs fluid from the reservoir of the 
master cylinder to the front wheels and fluid from the other reservoir to the rear wheels. The circuits are 
hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on 
the other. 

10

Right Rear Brake

11

Right Rear Outlet Valve

12

Left Rear Outlet Valve

13

Left Rear Brake

14

Left Rear Inlet Valve

15

Left Front Inlet Valve

16

Left Front Brake

17

Left Front Outlet Valve

18

Right Front Brake

19

Right Front Outlet Valve

20

Accumulator

21

Right Front Inlet Valve

22

Damper

23

Front Master Cylinder Isolation Valve

24

Front Prime Valve

IMPORTANT: There is a rubber isolator located under the BPMV and on the mounting 

 

2004 Hummer H2 

2004 BRAKES Anti-Lock Brake System - Hummer H2

  

The BPMV contains the following components: 

{

Pump Motor  

{

Inlet Valves (one per wheel)  

{

Outlet Valves (one per wheel)  

{

Master Cylinder Isolation Valves (w/NW9) (one per drive wheel)  

{

Prime Valves (w/NW9) (one per drive wheel)  

z

Longitudinal accelerometer (W/NW9) - The longitudinal accelerometer is used to determine straight-line 
acceleration. This information is used for Traction Control in the AWD, 4WD applications.  

z

Stoplamp Switch - The EBCM uses the stoplamp switch as an indication that the brake pedal is applied.  

z

Traction Control Switch, TC2 (w/NW9) - The TC2 is manually operated to enabled loose surface or road 
mode.  

z

Wheel Speed Sensors (WSS) - As the wheel spins, the wheel speed sensor produces an AC signal. The 
EBCM uses this AC signal to calculate wheel speed. Any imperfections in the toothed ring, such as a 
missing or damaged tooth, can cause an inaccurate WSS signal.  

Initialization Sequence 

The EBCM performs one initialization test each ignition cycle. The initialization of the EBCM occurs when one 
set of the following conditions occur: 

Both of the following conditions occur: 

z

The EBCM receives that there is a minimum of 500 rpm from the PCM via class 2 serial data message.  

z

The stoplamp switch is not applied.  

OR 

Both of the following conditions occur: 

z

The vehicle speed is greater than 16 km/h (10 mph).  

z

The stoplamp switch is applied.  

The initialization sequence may also be commanded with a scan tool. 

The initialization sequence cycles each solenoid valve and the pump motor (as well as the necessary relays) for 
approximately 1.5 seconds to check component operation. The EBCM sets a DTC if any error is detected. The 
initialization sequence may be heard and felt while it is taking place, and is considered part of normal system 
operation. 

The EBCM defines a drive cycle as the completion of the initialization sequence.

studs. The rubber isolators protect the BPMV and the EBCM from vehicle 
vibrations.

 

2004 Hummer H2 

2004 BRAKES Anti-Lock Brake System - Hummer H2