Diagnostic Process
When servicing the Antilock Brake System (ABS) follow, in order, the
following steps. Failure to follow these steps may result in the loss of important
diagnostic data and may lead to difficult and time-consuming diagnosis procedures:
- Perform a vehicle preliminary diagnosis inspection. This should
include the following:
| • | Inspect the master cylinder fluid reservoir for proper brake fluid
level. |
| • | Inspect the brake pressure modulator valve assembly for any leaks
or wiring damage. |
| • | Inspect the brake components at all four wheels. Verify that no
drag exists. Verify the proper operation of the base brake apply. |
| • | Inspect for worn or damaged wheel bearings that may allow a wheel
to wobble. |
| • | Inspect all wheel speed sensors and their wiring: |
| - | Verify proper sensor attachment |
| - | Verify that the sensor toothed ring is undamaged |
| - | Verify that the wiring is undamaged, especially at the vehicle
attachment points |
- Perform the
Diagnostic System Check - ABS
.
Self Diagnostics
The Antilock Brake System (ABS) contains sophisticated on-board diagnostics.
When accessed with a scan tool connected to the OBD2 Data Link Connector (DLC),
these diagnostics identify the source of any system malfunction as specifically
as possible.
The scan tool allows the technician to perform the following tasks:
| • | Access Diagnostic Trouble Codes (DTCs) which were set in previous
ignition cycles (also referred as history DTCs) and access an actual DTC set
(also known as a current DTC). |
| • | Obtain SNAP SHOT data for the last DTC code set. The SNAP SHOT
data includes the following: |
| - | The stoplamp switch status at the time when the last DTC set |
| - | This information is called Enhanced DTC Data. |
| • | Monitor the ABS inputs and the outputs with a scan tool. This
confirms the malfunction confirmation and verifies the repair. |
| • | Perform manual control of ABS components. |
