See Figures 1, 2, 3 and 4
System diagnosis begins with the Diagnostic Circuit Check or Function Test, depending on the application. Please refer to the charts located earlier 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.
Some of the diagnostic or repair procedures refer to the performance of a Function Test. This test is performed with the scan tool; it operates all components of the EHCU and checks their function. The test cannot be performed without the scan tool.
See Figures 5 and 6
Stored trouble codes may be transmitted through the flashing of the ANTILOCK dash warning lamp. On these vehicles, the system may be placed in diagnostic mode using a jumper wire, however, the use of the Tech 1®® scan tool or its equivalent is highly recommended.
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 -- refer to self-diagnostics in Emission Controls of this guide for more information) to either body ground or to terminal A (internal ground). The terminals must be connected for a few seconds before the code will transmit. Observe the ANTILOCK light on the dash and count the flashes in groups: 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, but 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 hand scanner if available or, using a jumper wire:
- If a hand scanner is available, use it to erase the computer module code memory.
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 ANTILOCK and BRAKE lamps should both illuminate and then extinguish.