Before reading trouble codes, perform the Diagnostic Circuit Check (DCC) or Function Test (FT) according to the appropriate charts for your vehicle. The charts are located in this section. This test will aid in separating 1 system problems from common problems in the hydraulic brake system. The diagnostic circuit check will direct the reading of trouble codes as necessary.
DO NOT ground the brake trouble code terminal of the ALDL/DLC if the BRAKE lamp is not on, indicating a stored trouble code. Attempting to activate trouble code readout with the BRAKE lamp off may set a false Code 9. This will turn the BRAKE lamp ON and disable the anti-lock brake system.
The following diagnostic flow charts may be used to help pinpoint Rear Wheel Anti-Lock (RWAL) system troubles.
See Figure 1
The computer control module (ECU/EBCM) will assign a code to the first fault found in the system. If there is more than one fault, only the first recognized code will the stored and transmitted.
Trouble codes may be read either though the use of a Tech-1 or equivalent scan tool, or by connecting a jumper wire from pin H on the ALDL/DLC to pin A. If the jumper method is used, the fault code will be displayed through the flashing of the BRAKE warning lamp on the dash. The terminals must be connected for about 20 seconds before the display begins. The display will begin with 1 long flash followed by shorter ones-count the long flash as part of the display.
Sometimes the first display sequence will be inaccurate or short; subsequent displays will be accurate.
If using a hand scanner, note if a soft code is stored; only the last recognized code will be retained and displayed on the scanner. Soft fault Codes 6, 9 and 10 (1989-93 models) or soft Codes 2, 3, 4, 6, 7, 8, 9, and 10 (1994-96 models) can only be read with a scan tool. On some models, Codes 1, 11 and 12 will not read on the scan tool and must be read using the jumper wire method.
Never ground terminal H of the ALDL to terminal A if the BRAKE warning lamp is not lit. Doing so will usually set a false code 9 and illuminate the BRAKE warning lamp. With the brake lamp on, the 1 system will be disabled.
Stored trouble codes must be cleared with the ignition switch OFF . NEVER attempt to clear codes while the ignition switch is in the ON position or the computer module will likely be destroyed. Remove the ECMB fuse for at least 5 seconds, then reinstall the fuse.
Some diagnostic procedures require the installation of a pinout box (J35592) in order to prevent damage to the 35-pin connector. The pinout box should be installed prior to probing any circuit with a digital multimeter.To install the pinout box:
- Ensure that the ignition switch is in the OFF position when removing the 35-pin connector.
- Unfasten the connector by depressing the locking plate and rotating the connector toward the front of the vehicle.
- Inspect the 35-pin connector for damage. Install the pinout box (J35592) on the connector.
- Proceed with the test.