Hummer H1 (2006+). Manual — part 241

7-46

Brake System

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Figure 7-46: ABS/TT4 Warning Light Sequence.

Anti-lock braking operates by continually sensing the speed of each wheel. Wheel speed information is transmitted to an Electronic
Control Unit (ECU) which evaluates the information to determine when any wheel is about to lock. If locking commences, the
ECU transmits a control signal to the appropriate solenoid valve in the modulator controlling hydraulic pressure to the brake, thus,
brake pressure is adjusted to maintain wheel rotation.

The TorqTrac 4 system uses many of the same components as the ABS to control wheel spin when accelerating the vehicle on low
friction surfaces. Information from the wheel speed sensors is evaluated by the ECU which determines if a wheel is loosing traction
and spinning. The ECU actuates the modulator pump to provide hydraulic pressure which is modulated by the solenoid valves and
sent to the brake of the spinning wheel. This has the effect of transferring the torque to the non-spinning wheel on the higher fric-
tion surface. The system has an overheat protection feature which disables TT4 after 60 seconds of continuous use. This will be in-
dicated by a blinking TT4 lamp. TT4 will automatically return to normal operation after a 60 second cool down period.

ABS/TT4 DIAGNOSTICS

Fault Diagnostic Procedure

Faults are stored in the ECU memory in code form. The information can be retrieved by initiating and reading a series of flash and
pause sequences (blink codes) on the ABS warning light or with the Wabco Diagnostic Controller.

Use of the blink code procedure will determine the location of the fault prior to performing physical wiring and component tests,
thus reducing diagnostic time.

NOTE: An attempt to initiate the blink code diagnostic may result in a solid “on” ABS warning lamp without progressing to the
start phase of the diagnostic. If the above condition is present, remove the ABS Warning Lamp Relay from the exterior fuse box
and perform the blink code diagnostic (See Figure 7-61). After repairs are completed, replace the warning lamp relay in the socket.

Blink Code Procedure

To initiate the blink code procedure, connect the blink code switch jumper J–44237 to the Diagnostic Link Connector (DLC) of the
vehicle. The jumper allows you to short pin 4 to pin 15 of the DLC.

Switch on the ignition, the ABS warning light will illuminate and extinguish if there are no active faults.

3 sec

ABS

Warning

Lamp

T T4 Info

Lamp

8-S07-002

ignition

T T4

3 sec

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Brake System 7-47

5745804

Five seconds after connecting the switch jumper, the ABS warning light will extinguish, indicating the start of the blink code
cycle.

The start phase consists of the ABS warning light flashing in the following sequence (Figure 7-47):

• Pause = 2.5 seconds (long)

• Flash = 2.5 seconds (long)

• Pause = 2.5 seconds (long)

• Flash = 0.5 seconds (short)

Figure 7-47: Blink Code Sequence For Start Phase.

Figure 7-48: Blink Code Sequence For Code 3.3.

The first part of the code number (Figure 7-48:): A pause of 2.5 seconds precedes a series of short flashes. Count the flashes
until the next long pause occurs. The number of short flashes obtained is the first part of the code number.

The second part of the code number: A pause of 2.5 seconds occurs between the first and second parts, before a series of short
flashes occurs. The number of short flashes forms the second part of the code number.

The sequence of the start phase, first and second parts will continue until the switch jumper is deactivated.

NOTE: If you are unsure of the code, do not deactivate the switch jumper from the DLC because the code for that fault will be
cleared from the memory.

It is possible to have more than one fault with the system at a time. However, the first indicated fault must be repaired then
cleared by reconnecting the jumper and awaiting the next start phase before the next fault code can be extracted.

Repeat the procedure until no further faults are stored in the memory. The memory is cleared when a long pause of 7.5 seconds
occurs after the start phase.

Clearing Fault Codes

At the end of a fault code cycle, deactivate the blink code jumper. The fault code will cycle one more time before the lamp remains
on solid. Turn off the ignition and the fault code will be cleared from memory.

The fault codes, their causes and repair actions are listed in the following table.

2.5 sec

0.5

sec

8-S07-003

ABS

Warning

Lamp

2.5 sec

8-S07-004

ABS

Warning

Lamp

0.5

sec

0.5

sec

2.5 sec

0.5

sec

0.5

sec

0.5

sec

0.5

sec

6-1-05

7-48

Brake System

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Fault Code List - Ignition key “OFF” to test system (except where noted)

Test pin locations refer to ABS Pinout Box J–35592

Fault Code

Problem Area

Test Pin

Locations

Values

Check/Repair

2-0

ECU internal failure.

Replace ECU.

2-1

ECU internal failure.

Replace ECU.

2-2

Recirculating Pump
(RCP) operates con-
tinuously.

12 and 27
30 and 27

Ignition “ON”
0 volts

Check the RCP wiring, the pump relay and the
wiring connections. Repair or replace as required.

2-2

RCP does not
operate.

Jumper 9 and
11
27 and 30

Ignition “ON”
approximate
battery +
voltage.

Check the RCP wiring, the pump relay and fuse
and pump connections. Repair or replace as
required.

2-4

RCP failure
(motor locked).

Jumper 9, 11
and 12

Ignition “ON”
RCP motor
running.

Excessive current failure. If pump does not run
with pins linked, check wiring and relays, if OK,
replace modulator.

2-6

Shuttle valve switch
failure.

25 and 27

Brake pedal at
rest 3k

Ω.

Brake pedal 1/
2 down 2k

Ω.

Brake pedal
full down 1k
Ω.

If wiring and connections OK, replace modulator.

2-7

Continuous power to
ECU with ignition
“OFF”.

9 and 27

0 volts.
Less than 0.2
Ω to chassis
ground.

Check for proper wiring connections, repair as
necessary.

2-8

No voltage to ABS
solenoid valves.

Jumper 8 and 9
19 and 27
1 and 27
9 and 27

Ignition “ON”
approximate
battery +
voltage.

Check the valve relay, fuse and wiring. Repair as
necessary.

2-9

Inlet valve supervi-
sion time exceded.

Check system voltage for normal function. Clear
fault.

2-10

Reference ground
interrupted.

Less than 0.2
Ω to chassis
ground.

Repair wiring or connection as necessary.

2-11

Excessive recircula-
tion pump cycle
time.

Ignition “ON”
jumper 9, 11
and 12

RCP running

Check RCP function. Clear fault.

2-12
2-13
2-14
2-15

RF sensor weak
LR sensor weak
LF sensor weak
RR sensor weak

17 and 34
18 and 35
15 and 32
16 and 33

Greater than
0.9 volts AC
at one tire rev-
olution per
second.

Check sensor adjustment. Check geared hub bear-
ing play at halfshaft. Adjust or repair as necessary.

6-1-05

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Brake System 7-49

5745804

3-0

Open circuit between
ECU and right front
inlet solenoid valve
or wiring.

6 and 27

5.0-7.5