Vehicle on-Board Diagnostics

The following information is to be used for reference when directed by the appropriate diagnostic procedure. Do not attempt to diagnosis an ABS condition starting here. The following procedure deals only with the aspects of entering the diagnostic service mode which are required for diagnosis of the anti-lock brake system.
1. Turn ignition switch to the On position. On CRT models, select the ``Climate'' screen by pressing the button in upper righthand corner.
2. On non-CRT models, press the Off and WARM buttons on the climate control panel simultaneously and hold until the segment check begins on the instrument panel cluster. On CRT models, touch Off and Warm pads simultaneously, until screen displays ``Service Mode'' configuration.
3. On non-CRT models, the segment check will cause the instrument panel cluster to illuminate and cycle all displays. The segment check takes approximately five seconds to complete.
4. On all models, after the segment check is completed, any trouble codes which have been stored by the ECM, BCM, IPC, or CRT will be displayed.
a. ECM trouble codes will be displayed first. If no ECM trouble codes are present, the ``NO ECM CODES'' message will appear. ECM codes are prefixed with an E. ECM codes are not relevant to ABS diagnosis.
b. BCM trouble codes will be displayed next. If no BCM trouble codes are present the ``NO BCM CODES'' message will appear. BCM codes are prefixed with a B. BCM code B482 applies to ABS diagnosis.
c. CRT code will be displayed next. If no CRT codes are present, ``No CRT Codes will appear. CRT codes are prefixed with a C. CRT codes are not relevant to ABS diagnosis.
5. All codes will be accompanied by a ``CURRENT'' or ``HISTORY'' designation. History indicates that the failure was not present the last time the code was tested. Current indicates the fault still exists. If BCM codes B482 is present, note if it is designated current or history before proceeding with the diagnosis procedure.
6. On non-CRT models, if the ``LO FAN'' (down arrow), button on the climate control panel, or on CRT models, the ``NO'' pad is depressed at any time during the display of the ECM or BCM diagnostic codes, the code display will be bypassed. On non-CRT models, if the ``BI-LEVEL'' button, or on CRT models, the ``END'' pad is depressed at any time during the code display, the system will exit the diagnostic service mode and resume normal vehicle operation.
7. After the trouble codes have been displayed, the computer system allows one of two vehicle systems to be selected for testing, on non-CRT models, and one of four vehicle systems on CRT models. At this time, the driver information center displays the first available system as indicated by the ECM message. Three responses are possible:
a. Bypass ECM system test is activated by pressing the ``LO FAN'' (down arrow), button, on non-CRT models, and the ``NO'' pad on CRT models. This should be done if ABS diagnosis is desired.
b. Display trouble codes again by pressing the OFF button on non-CRT models, or the ``LEVEL'' pad on CRT models. This should be done if you need to review the code display.
c. Exit diagnostic mode by pressing the ``BI-LEV'' button on non-CRT models, or the ``END'' button on CRT models. This will resume normal vehicle operation.
8. After bypassing the ECM test system, the climate control driver information center will display, the prompt BCM. This mode should be selected by depressing the ``HI FAN'' (up arrow), button on non-CRT models, or the ``YES'' pad on CRT models.
9. After entering BCM diagnostic mode. The anti-lock brake system inputs to the BCM can be monitored. The BCM input feature of diagnostic service mode is accessed as follows:
a. After entering BCM diagnostic mode, the driver information center will display the prompt ``BCM DATA.'' You should respond to this by pressing the ``LO FAN'' (down arrow), button on non-CRT models, or ``NO'' pad on CRT models.
b. The driver information center will then display the prompt ``BCM INPUTS.'' You should respond to this by pressing the ``HI FAN'' (up arrow), button on non-CRT models, or ``YES'' pad on CRT models. This will place the system in BCM input mode.
c. The system will now show the status of selected BCM inputs, Inputs which are relevant to the anti-lock brake system include BI18, BI21 and BI22.
10. While in the input mode, the BCM can display the status of up to 18 different inputs. Each input is designated with an identifier such as BI21, meaning BCM input 21. In order to display a BCM input which is higher or lower in number than the one currently on the display, press the ``HI FAN'' (up arrow), button on non-CRT models, or the ``YES'' pad on CRT models, to increment the display. On non-CRT models, press the ``LO FAN'' (down arrow), or the ``NO'' pad on CRT models, to lower the numbered display. Each of these input displays will appear in the same format. All displays are normally HI. A warning input to the BCM would appear as a LO status indication.
11. After evaluating the ABS inputs to the BCM in conjunction with the correct diagnostic procedures, exit diagnostic service mode by depressing the ``BI-LEV'' button on non-CRT models, or the ``END'' pad on CRT models. This will return the computer system to normal operation.