Opel Frontera UE. Manual - part 121

5A–30

BRAKE CONTROL SYSTEM

Symptom Diagnosis

The symptoms that cannot be indicated by warning light 
can be divided in the following five categories:

1. ABS works frequently but vehicle does not 

decelerate.

2. Uneven braking occurs while ABS works.

3. The wheels lock during braking.

4. Brake pedal feel is abnormal.

5. Braking sound (from EHCU) is heard while not 

braking.

These are all attributable to problems which cannot be 
detected by EHCU self-diagnosis.   Use the customer 
complaint and a test to determine which symptom is 
present.   Then follow the appropriate flow chart listed 
below.

Chart A-1 ABS Works Frequently But Vehicle Does Not Decelerate

No.

Symptom

Diagnostic Flow Charts

Without TECH 2

With TECH 2

1

ABS works frequently but vehicle does not decelerate.

Chart A-1

Chart TA-1

2

Uneven braking occurs while ABS works.

Chart A-2

Chart TA-2

3

The wheels are locked.

Chart A-3

Chart TA-3

4

Brake pedal feel is abnormal.

Chart A-4

—

5

Braking sound (from EHCU) is heard while not braking. 

Chart A-5

Chart TA-5

Step

Action

Yes

No

1 

Is braking force distribution normal between front and rear of 
vehicle?

Go to Step 2

Repair brake 

parts.

Go to Step 8

2 

Are axle parts installed normally?

Go to Step 3

Repair axle 

parts.

Go to Step 8

3 

Is there play in each or any wheel speed sensor?

Repair wheel 

speed sensor.

Go to Step 8

Go to Step 4

4 

Is there damage, or powered iron sticking to each or any wheel 
speed sensor/sensor ring?

Replace sensor 

or sensor ring.

Go to Step 8

Go to Step 5

5 

Is the output of each wheel speed sensor normal? (Refer to chart 
C-1 or TC-1)

Go to Step 6

Replace wheel 

speed sensor or 

repair harness.

Go to Step 7

6 

Is the input of 4WD controller normal?

Go to Step 7

Replace 

controller or 

repair harness.

Go to Step 7

7 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 7

BRAKE CONTROL SYSTEM

5A–31

Chart TA-1 ABS Works Frequently But Vehicle Does Not Decelerate (Use TECH 2)

Chart A-2 Uneven Braking Occurs While ABS Works

Chart TA-2 Uneven Braking Occurs While ABS Works (Use TECH 2)

Step

Action

Yes

No

1 

1. Connect TECH 2.

2. Make sure of the output conditions of each sensor.

Is the output of each sensor normal?

Go to Step 2

Replace wheel 

speed sensor.

Go to Step 3

2 

Return to Chart A-1.
Was the Chart A-1 finished?

Go to Step 3

Go to Step 2

3 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 3

Step

Action

Yes

No

1 

Is there play in each or any sensor?

Repair.

Go to Step 5

Go to Step 2

2 

Damage or powdered iron sticking to each or any sensor/sensor 
ring?

Repair.

Go to Step 5

Go to Step 3

3 

Is the output of each sensor normal? (Refer to chart C-1 or TC-1)

Go to Step 4

Replace sensor 

or repair 

harness.

Go to Step 5

4 

Is brake pipe connecting order correct?

Replace H/U.

Go to Step 5

Reconnect 

brake pipe 

correctly.

Go to Step 5

5 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 5

Step

Action

Yes

No

1 

1. Connect TECH 2.

2. Make sure of the output conditions of each sensor.

Is the output of each sensor normal?

Go to Step 2

Go to Step 3

2 

Check piping by TECH 2 ACTUATOR TEST
Is the piping normal?

Replace EHCU.

Go to Step 4

Repair the pipe.

Go to Step 4

3 

Repair and check the wheel speed sensor (Refer to chart B-20 to 
B-23 , C-1 or TC-1).
Was the each chart finished?

Go to Step 4

Go to Step 3

4 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 4

5A–32

BRAKE CONTROL SYSTEM

Chart A-3, TA-3  The Wheels Are Locked

Chart A-4 Brake Pedal Feed Is Abnormal

Step

Action

Yes

No

1 

Is ABS working?

Go to Step 2

Go to Step 6

2 

Is vehicle speed under 10 km/h (6mph)?

Normal.

Go to Step 3

3 

Is sensor output normal? (Chart C-1 or TC-1)

Go to Step 4

Replace sensor 

or repair 

harness.

Go to Step 6

4 

Is front 4WD controller normal?

Go to Step 5

Replace 4WD 

controller or 

repair harness.

Go to Step 6

5 

Is hydraulic unit grounded properly?

Replace EHCU.

Go to Step 6

Correct.

Go to Step 6

6 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 6

Step

Action

Yes

No

1 

Is the stop light actuated when the brake pedal is depressed?

Go to Step 2

Go to Step 3

2 

1. Turn the ignition switch off.

2. Disconnected EHCU connector.

Is the check voltage EHCU connector terminals 13 to 7 when 
brake pedal is depressed than battery voltage?

Go to Step 4

Harness NG 

between brake 

SW and EHCU.

Go to Step 6

3 

Is stop light fuse normal?

Go to Step 5

Replace stop 

light fuse.

Go to Step 6

4 

Is the check continuity between EHCU connector terminals, 7 to 
body grounded?

Go to Step 6

Repair body 

grounded 

harness.

Go to Step 6

5 

Is brake SW normal?

Repair stop 

light harness.

Go to Step 6

Replace brake 

SW.

Go to Step 6

6 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 6

BRAKE CONTROL SYSTEM

5A–33

Chart A-5, TA-5 Braking Sound (From EHCU) Is Heard While Not Braking

Step

Action

Yes

No

1 

Is this the first vehicle start after engine start?

It is self 

checking sound

Normal.

Go to Step 2

2 

Is vehicle speed under 10 km/h (6 mph)?

It is self 

checking sound

Normal.

Go to Step 3

3 

Check for the following condition:

• At the time of shift down or clutch operation.

• At the time of low road friction drive (ice or snow road) or rough 

road drive.

• At the time of high-speed turn.

• At the time of passing curb.

• At the time of operating electrical equipment switches.

• At the time of racing the engine (over 5000 rpm).
Did it occur under any one condition above?

ABS may 

sometime be 

actuated even 

when brake pedal 

is not applied.

Go to Step 4

4 

Is there play in each or any sensor/wheel speed sensor rings?

Repair.

Go to Step 7

Go to Step 5

5 

Damage or powdered iron sticking to each or any sensor/wheel 
speed sensor ring?

Repair.

Go to Step 7

Go to Step 6

6 

Is each sensor output normal? (Refer to chart C-1 or TC-1).

Check harness/ 

connector for 

suspected 

disconnection

If no 

disconnection is 

found, replace 

Coil integrated 

module.

Go to Step 7

Repair.

Go to Step 7

7 

Reconnect all components, ensure all components are properly 
mounted.
Was this step finished?

Repeat the “Basic  

diagnostic flow 

chart"

Go to Step 7