5A4-30 ANTI-LOCK BRAKE SYSTEM (ABS) Symptom Diagnosis The symptoms that cannot be indicated by the 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 Hydraulic Unit) 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 Chart TA-1 ABS Works Frequently But Vehicle Does Not Decelerate (Use TECH 2) 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 Hydraulic Unit) is heard while not braking. Chart A-5 Chart TA-5 Step Action Yes No 1 Is braking force distribution normal between the front and rear of the vehicle? Go to Step 2 Repair brake parts.
Go to Step 6 2 Are axle parts installed normally? Go to Step 3 Repair axle parts. Go to Step 6 3 Is there play in each wheel speed sensor? Go to Step 4 Repair wheel speed sensor. Go to Step 6 4 Is there damage, or powdered iron sticking to each wheel speed sensor/sensor rotor? Go to Step 5 Replace sensor or sensor rotor. Go to Step 6 5 Is the output of each wheel speed sensor normal? (Refer to chart C-1 or TC-1) Replace EHCU. Go to Step 6 Replace wheel speed sensor or repair harness. Go to Step 6 6 Reconnect all components and 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 1. Connect TECH 2. 2.
WHEEL SENSORS 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