Antilock Brakes / Traction Control Systems: Service Precautions
PRECAUTIONWhen inspecting or servicing the ABS, note the following points:
1. The ABS warning light illuminates even when the system is normal.
The ABS warning light may illuminate under the following cases, even when the system is normal.
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.
1) Malfunctions in electrical system
- The ABS Control Module (ABS CM) has an on-board diagnostic function. With this function, the ABS warning light comes on when there is a problem in the electrical system. Also, past and present malfunctions are recorded in the ABS CM. This function can find malfunctions that do not occur during periodic inspections. Connect the Special Service Tool (SST) New Generation Star (NGS) then turn the ignition switch to ON 5 seconds later the stored malfunctions will be displayed in the 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.
- After repair, it is necessary to clear the Diagnostic Trouble Code (DTC) from the ABS CM memory. Also, if the ABS related parts have been replaced, verify that no DTC has been displayed after repairs.
- After repairing the ABS wheel-speed sensor or replacing the ABS motor (built in ABS hydraulic unit (HU)), 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 clear the DTC.
- When repairing, if the ABS related connectors are disconnected and the ignition switch is turned on, the ABS CM will mistakenly detect a fault and record it as a malfunction.
- To protect the ABS CM, make sure the ignition is off before connecting or disconnecting the ABS CM connector.
- To protect the terminals, use the SST when connecting the tester lead to the ABS CM connector.
2) Malfunctions in hydraulic system
- Symptoms in a hydraulic system malfunction are similar to conventional brake symptoms. However, it is necessary to determine if the malfunction is in an ABS component or the conventional brake system.
- The HU 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).