See Figures 1, 2, 3 and 4
Diagnosis of the ABS system consists of 3 general steps, performed in order:
- The visual or preliminary inspection, including inspection of the basic brake system, is always required before any other steps are taken.
- Initial diagnosis is then made by a careful analysis of the ANTI-LOCK Warning Lamp display during start-up and operation. The warning lamp troubleshooting chart will direct the use of further charts and detailed testing based on initial findings.
- The ABS system may be further checked with the DRB-III, MUT-II or equivalent diagnostic scan tool, provided the correct cartridges are used. The scan tool, will allow various components of the system to be operated for testing purposes. Connect the scan tool according to instructions furnished with the tool. The system will enter diagnostic mode and prompt the operator through the assorted system checks and tests.
Remember to first determine if the problem is related to the anti-lock system or not. The anti-lock system is made up of 2 basic sub-systems:
- The hydraulic system, which may be diagnosed and serviced using normal brake system procedures, however, there is a need to determine whether the problem is related to the ABS components or not.
- The electrical system which may be diagnosed using the charts and diagnostic tools.
Before diagnosing an apparent ABS problem, make absolutely certain that the normal braking system is in correct working order. Many common brake problems (dragging lining, seepage, etc.) will affect the ABS system. A visual check of specific system components may reveal problems creating an apparent ABS malfunction. Performing this inspection may reveal a simple failure, thus eliminating extended diagnostic time.
- Inspect the brake fluid level in the reservoir.
- Inspect brake lines, hoses, master cylinder assembly, and brake calipers for leakage.
- Visually check brake lines and hoses for excessive wear, heat damage, punctures, contact with other parts, missing clips or holders, blockage or crimping.
- Check the calipers for rust or corrosion. Check for proper sliding action if applicable.
- Check the caliper pistons for freedom of motion during application and release.
- Inspect the wheel speed sensors for proper mounting and connections.
- Inspect the toothed wheels for broken teeth or poor mounting.
- Inspect the wheels and tires on the vehicle. They must be of the same size and type to generate accurate speed signals. Check also for approximately equal tire pressures.
- Confirm the fault occurrence with the operator. Certain driver induced faults may cause dash warning lamps to light. Excessive wheel spin on low-traction surfaces or high speed acceleration may also set fault codes and trigger a warning lamp. These induced faults are not system failures but examples of vehicle performance outside the parameters of the controller.
- The most common cause of intermittent faults is not a failed sensor but a loose, corroded or dirty connector. Incorrect installation of the wheel speed sensor will cause a loss of wheel speed signal. Check harness and component connectors carefully.
If the battery on the vehicle has been completely drained, always recharge the battery before driving. If the vehicle is driven immediately after jump starting, the ABS self-check may draw enough current to make the engine run improperly. An alternate solution is to disconnect the ABS connector at the hydraulic unit. This will disable the ABS and illuminate the dash warning lamp. Reconnect the ABS when the battery is sufficiently charged.