Anti-Lock/Traction Control System: Abs: Precaution

When inspecting or servicing the ABS, note the following points:

1. The ABS warning light and/or BRAKE system warning light illuminate even when the system is normal.
   Fig 1: Warning Light Diagnosis

   Courtesy of MAZDA MOTORS CORP.
2. Precautions during servicing of ABS

   The ABS is composed of electrical and mechanical parts. It is necessary to categorize malfunctions as being either electrical or hydraulic when performing troubleshooting.

   • Malfunctions in electrical system:
     • The ABS hydraulic unit and control module (ABS HU/CM) has an on-board diagnostic function. With this function, the ABS warning light and/or BRAKE system warning light will come on when there is a problem in the electrical system. Also, past and present malfunctions are recorded in the ABS HU/CM. This function can find malfunctions that do not occur during periodic inspections. Turn the ignition switch on by connecting the SST  (WDS or equivalent) to the DLC-2 inside the Passenger comportment. Approximately 5 seconds  later the stored malfunctions will be displayed in order of occurrence. To find out the causes of ABS malfunctions, use these on-board diagnostic results.
     • If a malfunction occurred in the past but is now normal, the cause is likely a temporary poor connection of the harness. The ABS HU/CM usually operates normally. Be careful when searching for the cause of malfunction.
     • After repair, it is necessary to erase the DTC from the ABS HU/CM memory. Also, if the ABS related parts have been replaced, verify that the no DTC has been displayed after repairs.
     • After repairing the ABS wheel-speed sensor or ABS sensor rotor, or after replacing the ABS HU/CM (ABS motor or ABS motor relay or solenoid valve), the ABS warning light may not go off even when the ignition switch is turned on. In this case, drive the vehicle at a speed of more than 10 km/h {6.2 MPH}  , make sure the ABS warning light goes off, and then erase the DTC.
     • When repairing, if the ABS related connectors are disconnected and the ignition switch is turned on, the ABS HU/CM will mistakenly detect a fault and record it as a malfunction.
     • To protect the ABS HU/CM, make sure the ignition is off before connecting or disconnecting the ABS HU/CM connector.
     • To protect the terminal, use the SST  (49 G066 001) when connecting the tester lead to the ABS HU/CM connector.
   • Malfunctions in hydraulic system
     • Symptoms in a hydraulic system malfunction are similar to those in a conventional brake malfunction. However, it is necessary to determine if the malfunction is in an ABS component or the conventional brake system.
     • The ABS hydraulic unit contains delicate mechanical parts. If foreign materials get into the component, the ABS may fail to operate. Also, it will likely become extremely difficult to find the location of the malfunction in the event that the brakes operate but the ABS does not. Make sure foreign materials do not get inside when servicing the ABS (e.g. brake fluid replacement, pipe removal).