Intermittent Problems

FINDING A FAULTY CIRCUIT
With intermittent faults, you can use the ABS system's self-diagnosis facility to help decide which circuit might be faulty, as follows:
1. Read off, note down and erase any DTCs for the ABS system which may be stored in the control module.
2. Test drive the car, trying to repeat the conditions under which the fault occurred. Details of the conditions when the fault occurred may help in fault-tracing.
3. Stop the car and read off any DTCs which have been posted.

If the fault does not recur during the test drive, a good description of what the car was doing when the problem arose may be a great help in looking for the circuit or component which is most probably at fault. Most intermittent problems are due to faults in connections and leads. With intermittent faults, check suspect circuits for: Poor connections between connectors or lead terminals which have not been pushed together completely. Poorly connected or damaged connectors. Poor connections between terminates and leads. Most faults which occur with an ABS system mean the system's anti-lock capability is lost completely while driving, even if the fault disappears before the ignition is switched off. The normal, hydraulic braking function remains all the time. With some intermittent faults, however, the ABS function may return if the fault disappears before the ignition is switched off.

The conditions below may mean that the ABS warning light comes on temporarily. Check the circuits for these input signals to the control unit if the customer says that the warning light comes on now and then.

CONTROL MODULE RESPONSE TO FAULTY POWER SUPPLY
If the power supply voltage is too high or too low, the control module will switch off the system and switch the ABS warning light on. The light will go out and the system work normally as soon as the voltage is correct. No DTC is posted if the battery voltage is faulty. The control module voltage limits are as follows: Low voltage, 9.4 ± 0.6 volts. High voltage, 20 ± 1.5 volts. If the power supply to the control module is interrupted temporarily, the control module may switch itself off and switch the ABS warning light on without posting a DTC.

FAULTS WHICH DO NOT GENERATE DTCs
Some faults may arise without any immediate indication via a DTC as in the tables. Finding the cause of the fault involves fault-tracing step by step to find the fault, using secondary DTCs and ruling out possible causes of the fault in turn.