Accessing and Reading Diagnostic Trouble Codes
Description:
The following information is to be used for reference when directed by the appropriate diagnostic procedure. Do not attempt to diagnose an ABS condition starting here. The following procedure deals only with the aspects of entering diagnostic Service Mode which are required for diagnosis of the Anti-Lock Brake System.
1. Ignition On - Ignition must be on to enter diagnostic "Service Mode." Remember that ABS trouble codes (EBCM codes) are erased when the ignition is turned off. In order to read ABS trouble codes, diagnostic mode must be entered during the ignition cycle in which the code was set.
2. Release Parking Brake - Be sure that the parking brake is fully released prior to beginning ABS trouble code diagnosis. If there is any doubt regarding whether or not the parking brake switch may be causing the BRAKE lamp to turn on, disconnect the harness connector at the parking brake pedal switch.
3. Entering "Service Mode" - Press the "OFF" and "WARMER" buttons on the Climate Control Panel simultaneously and hold until the segment check begins on the Instrument Panel Cluster (IPC) and Climate Control/Driver Information Center (CCDIC). See step A.
4. Segment Check - The segment check will cause the IPC and CCDIC to illuminate and cycle all displays. The segment check takes approximately five seconds to complete.
5. Code Display - After the segment check is completed, any trouble codes which have been stored by the ECM and Body Computer Module (BCM) will be displayed.
A. ECM Codes - ECM trouble codes will be displayed first. If no ECM trouble codes are present, the "NO ECM CODES" message will appear on the CCDIC. ECM codes are prefixed with an "E" (i.e. E013, E022). ECM codes are not relevant to ABS diagnosis.
B. BCM Codes - 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" (i.e. B110, B420, etc.). BCM codes B421, B480 and B481 are relevant to ABS diagnosis. Be alert to the presense of these codes during this phase of diagnosis.
C. Lighting Codes - Lighting trouble codes will be displayed last. Lighting code format is similar to ECM and BCM codes except that the prefix "L" is used. Lighting codes are not relevant to ABS diagnosis.
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 for and "CURRENT" indicates that the fault still exists. If BCM codes B421, B480 or B481 are present, note if they are designated CURRENT or HISTORY before proceeding with diagnosis.
If the "LO" button on the Climate Control Panel (CCP) is depressed at any time during the display of ECM or BCM diagnostic codes, the code display will be bypassed. If the "RESET" button is depressed at any time during display of codes, the system will exit diagnostic service mode and resume normal vehicle operation.
6. Selecting ABS Test Mode - After trouble codes have been displayed, the computer system allows any one of four systems to be selected for testing. At this point, the CCDIC displays the first available system as indicated by the "ECM?" message. Three responses are possible.
A. Bypass ECM test system by pressing the "LO" button. This should be done if ABS diagnosis is desired, as shown in step B.
B. Display ECM and BCM trouble codes again by pressing the "OFF" button. This should be done if it is desired to review the code display.
C. Exit diagnostic mode by pressing the "RESET" button. This will resume normal vehicle operation.
After bypassing the ECM test system, the CCDIC will display the next available system with the prompt "BCM?". This system should also be bypassed by depressing the "LO" button, as shown in step C.
After bypassing the BCM system, the "LIGHTING?" prompt will appear. It also should be bypassed with the "LO" button, as shown in step D. "ANTI-LOCK BRAKES?" will now appear on the CCDIC. This mode should be selected by depressing the "HI" button, as shown in step E.
7. Displaying ABS Codes - After selecting the Anti-Lock Brake Mode, the CCDIC will display the "KEEP BRAKE DEPRESSED" message as shown in step F, second illustration. The technician should now depress the brake pedal and hold it in the applied position. After approximately five seconds, the CCDIC will display the "COUNT LAMP FLASHES" message (step G,). The technician should now watch the red BRAKE warning lamp on the instrument panel cluster (IPC) and count the number of times the lamp flashes. Lamp flashes should be interpreted as described below.
8. Interpreting Lamp Flashes - The Anti-Lock Brake System may display any one of sixteen trouble codes through the lamp flash sequence. The number of times that the lamp flashes is equivalent to the code number (i.e. two flashes equals a Code 2, fifteen flashes equals a Code 15, etc.). To avoid misinterpretation of ABS code displays, the following information must be carefully reviewed.
If The Brake Lamp Does Not Come On At All
No ABS Codes are present. Attempt to reverify complaint or use symptom diagnosis methods as directed by appropriate diagnostic procedure.
If The Brake Lamp Remains On Continuously Throughout The Diagnostic Procedure
See symptom diagnosis information as directed by the ABS Functional Check. Diagnostic Charts
If The Brake Lamp Flashes Diagnostic Codes
Interpret the codes as follows:
^ ABS codes consist of short flashes of the brake light (approximately two flashes per second). Flashes of longer duration should be ignored.
^ If the pedal is continuously held down when in ABS diagnostic mode, the ABS code will repeat after an 11 second delay.
^ In some cases, the brake light will come on for 4.5 seconds during the period between code displays. This 4.5 second display of the brake light should not be interpreted as a flash.
9. Exiting Service Mode - After interpreting ABS diagnostic codes, exit Service Mode by depressing the "RESET" button. This will return the computer system to normal operation.
10. Return to the appropriate diagnostic procedure.