System diagnosis begins with the Diagnostic Circuit Check (DCC) or Function Test (FT), depending on the application. Refer to the charts located in this section. If the chart is used correctly, it will aid in elimination of simple, non-system problems such as blown fuses, failed bulbs or non-ABS related brake failures. The chart will prompt the reading of codes at the proper point in the diagnosis.
A function test is performed with a scan tool; it operates all components of the EHCU/BPMV and checks their function. The test cannot be performed without the scan tool.
See Figures 1, 2, 3, 4 and 5
Stored trouble codes may be transmitted through the flashing of the ANTI-LOCK dash warning lamp. The system may be placed in the diagnostic mode using a jumper wire, however, the use of the Tech-1 scan tool or equivalent is highly recommended. For all systems, the scan tool will allow performance of the specific system tests called for by the trouble tree'' for each code.
On vehicles where flash-diagnosis is possible, trouble code read out may be started using a jumper wire to connect Terminal H on the ALDL/DLC (diagnostic connector located under the instrument panel) to either a body ground or to terminal A (internal ground). The terminals must be connected for a few seconds before a code will transmit. Observe the ANTI-LOCK light on the dash and count the flashes in groups: for example, a group of 4 flashes, a pause and a group of 3 flashes indicates Code 43.
Remember that trouble codes cannot specify the exact cause of the problem, and may only relate which circuit is affected by the problem. Before replacing any component, be sure that it is the cause of the problem, especially when dealing with a control module fault. Control modules are quite expensive and are usually not returnable.
Stored codes may be erased with the scan tool, if available, or by using a jumper wire:
- If a hand-held scanner is available, use it to erase the computer module code memory.
- On some VCM equipped models, a code cannot clear on the same ignition cycle it was set. Before attempting to clear the code using a scan tool, it may be necessary to cycle the ignition to the OFF position for at least 10 seconds, then back to ON again to start another cycle.
Except for VCM equipped models, codes may be cleared without a scan tool as follows:
- Turn the ignition switch ON , but do not start the engine.
- Use a jumper wire to ground ALDL/DLC terminal H to terminal A for 2 seconds.
- Remove the jumper wire for 1 second.
- Repeat the grounding for 2 more seconds.
- When the trouble codes are cleared, the ANTI-LOCK and BRAKE lamps should both illuminate and then extinguish.