- Some vehicles are equipped with a Supplemental Inflatable Restraint (SIR) or air bag system. The air bag (SIR) system must be disabled before performing service on or around SIR components or wiring. Failure to follow safety and disabling procedures could result in possible air bag deployment, personal injury or unnecessary SIR system repairs.
- The use of rubber hoses or parts other than those specified for the ABS system may lead to functional problems and/or impaired braking or ABS function. Install all components included in repair kits for this system. Lubricate rubber parts with clean fresh brake fluid to ease assembly. Do not use lubricated shop air to clean or dry components; damage to rubber parts may result.
- Certain components in the ABS/TCS system are not intended to be serviced or disassembled. Only those components with removal and installation procedures should be serviced.
- Always disconnect the EBCM and PMV connectors before any welding is done on the vehicle.
- Never connect or disconnect the EBCM or PMV connectors with the ignition ON .
- Use only brake fluid from an unopened container. Use of suspect or contaminated brake fluid can reduce system performance and/or durability.
- When any hydraulic component or line is removed or replaced, it may be necessary to bleed the entire system.
- A clean repair area is essential. Perform repairs after components have been thoroughly cleaned.
- The EBCM is a microprocessor similar to other computer units in the vehicle. Insure that the ignition switch is OFF before removing or installing controller harnesses. Avoid static electricity discharge at or near the controller.
- Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test.
- Always wear a grounded wrist strap when servicing any control module or component labeled with a Electrostatic Discharge (ESD) symbol.
- Avoid touching module connector pins.
- Leave new components and modules in the shipping package until ready to install them.
- To avoid static discharge, always touch a vehicle ground after sliding across a vehicle seat or walking across carpeted or vinyl floors.
- Never allow welding cables to lie on, near or across any vehicle electrical wiring.
- Do not allow extension cords for power tools or droplights to lie on, near or across any vehicle electrical wiring.
Diagnosis of the anti-lock and/or traction control system consists of 3 steps which must be performed in order.
- Visual inspection
- Functional check
- Additional TESTING as specified by the functional check.
Some diagnostic procedures require that the ignition be left ON for an extended period of time while TESTING. Low battery voltage may result, causing incorrect readings or impaired system function. It is recommended that a battery charger be connected and a slow charge applied during TESTING.Visual Inspection
The initial visual inspection requires a thorough external check of both the conventional and ABS/TCS systems. Many faults are caused by items such as loose connectors, corroded grounds, failed fuses or low fluid levels. The visual inspection, when properly performed, will reveal these faults. Check the parking brake lever and cables for full release. Check the hydraulic system for leakage, line damage or restriction. System connectors should be tested for tightness; if a connector is suspect or has been exposed to moisture, separate the halves and check for corrosion on the terminal pins. Check connector shells for pin separation or push-out. Fuses in both the underdash and underhood panels should be checked. Correct the fluid level in the reservoirs if necessary.Functional Check/Displaying Codes
See Figures 1 and 2
If no problem is found during the Visual Inspection, the functional check must be performed. This test requires the use of a bi-directional hand-scanner, such as the General Motors Tech 1® or its equivalent. The scan tool is used to recover and/or clear stored fault codes during TESTING. The procedure also includes test driving the vehicle if necessary. Once fault codes or symptoms are determined, the test chart directs the use of the appropriate supplementary chart.
If multiple codes are stored, diagnose the code which first appears on the hand scanner.
Faults which occur intermittently are difficult to diagnose. When diagnosing such problems, keep an overall view of system function in mind. Faults may result from low system voltage, low brake fluid in the PMV reservoir or any interruption of the signal(s) from the wheel speed sensor(s). Any condition interrupting the power supply to the EBCM or hydraulic unit will also cause the dash warning lamp to illuminate. Most intermittent or random faults relate to loose connectors or faulty terminals. Again, the visual inspection is of prime importance.
The diagnostic codes can be helpful in tracking intermittent faults. While not designated History or Current, certain combinations can point to fault status. Stored codes which do not light the ANTI-LOCK warning lamp are intermittent or history codes. If the ANTI-LOCK lamp is lit and one or more codes are stored, at least one (or more) of the codes is current.
Additionally, when diagnosing intermittent faults, keep the following system basics in mind:
- It is possible to feel the system self-test at very low speed if the brake pedal is barely applied. Both the sound (fluid returning to the master cylinder) and the slight vibration (valves cycling through test mode) are normal conditions.
- Any fault in the anti-lock system will light the TRACTION light. When both lamps are lit, diagnose the ABS system.
- The systems will disable if either the EBCM senses overheating in the brakes or transaxle. Once cooled, the ABS/TCS becomes available and the dash lamp(s) extinguish. This self-protective operation is completely normal but may become a source of operator concern.
- When diagnosing an apparent TCS fault, make certain the TCS OFF switch is not engaged.
- If a faulty wheel speed signal is suspected, check tires and wheels for matching sizes and tire pressures.
- If necessary, the vehicle must be test driven to recreate circumstances causing the fault.
The operator of the vehicle is the best source of information about fault occurrences. An accurate description of driving conditions will allow the fault to be duplicated during the test drive.
- Display, record and clear all fault codes in the EBCM.
- Test drive the vehicle, attempting to recreate the failure conditions.
- Safely stop the vehicle. Display and record the stored codes, if any.
- If codes were stored, refer to the appropriate diagnostic chart. If no codes were stored, refer to the symptom chart.
Stored fault codes must be cleared using the bi-directional hand scanner. After repairs are completed, clear all stored codes and test drive the vehicle. Recheck for any newly-stored codes after the test drive.