Accessing and Reading Diagnostic Trouble Codes
ENTERING ABS/TCS DIAGNOSTIC SERVICE MODE
Important
^ The following information is to be used for reference when directed by the appropriate diagnostic procedure. Do not attempt to diagnose an ABS/TCS condition starting here. The following procedure deals only with the aspects of entering diagnostic Service Mode which are required for diagnosis of the Antilock Brake and Traction Control System.
1. Ignition On
Ignition must be on to enter diagnostic Service Mode.
2. Release Parking Brake
Be sure that the parking brake is fully released prior to beginning 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, in the illustration.
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 code E069 is relevant to ABS/TCS diagnosis. Be alert to the presence of this code during this phase of 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 B483 are relevant to ABS/TCS diagnosis. Be alert to the presence of these codes during this phase of diagnosis.
C. Lighting Codes
Lighting trouble codes will be displayed next. Lighting code format is similar to ECM and BCM codes except that the prefix is used. Lighting codes are not relevant to ABS diagnosis.
D. Restraint Codes
Restraint trouble codes will be displayed last. Restraint code format is similar to ECM and BCM codes except that the prefix R is used. Restraint 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, B483, or E069 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. Begin output of ABS/TCS diagnostic codes. Proceed to Step 7 if ABS/TCS diagnosis is desired.
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. See Step B, in the illustration.
C. Exit diagnostic mode by pressing the RESET button. This will resume normal vehicle operation.
7. Displaying ABS/TCS Codes.
To read EBCM flash codes, the vehicle must remain in diagnostic mode. To begin the flash code sequence, place a jumper wire between pin A and pin H of the Assembly Line Data Link (ALDL) connector. The ALDL connector is located in the trim panel near the park
Once the jumper is in place, observe the red BRAKE warning lamp on the IPC and count lamp flashes. Lamp flashes should be interpreted as described below.
8. Interpreting Lamp Flashes.
The EBCM may display any one of seventeen trouble codes through the lamp flash sequence. Trouble codes consist of two digits, the BRAKE lamp will flash the first digit, followed by a one second delay, then the second digit will be flashed. Each trouble code is flashed three times. The number of times that the lamp flashes is equivalent to the value of the digit.
To avoid misinterpretation of code display, the following information must be carefully reviewed. Use the second illustration as a reference.
IF THE BRAKE LAMP ONLY FLASHES CODE 12
^ No codes are present. Attempt to duplicate the complaint or use the symptom diagnosis methods as directed by appropriate diagnostic procedure.
IF THE BRAKE LAMP REMAINS ON CONTINUOUSLY THROUGHOUT THE DIAGNOSTIC PROCEDURE
^ Verify that on-board diagnostic mode has been entered by pressing OFF and WARMER. On-board diagnostic mode has been entered when displaying ABS/TCS fault codes. Since the BCM commands the BRAKE lamp to turn on, displaying trouble codes is not possible unless the BRAKE light is off before grounding ALDL pin H. The BCM shuts off the lamp when on-board diagnostic mode is entered.
^ See symptom diagnosis information as directed by ABS/TCS Functional Check, please refer to Symptom Diagnosis Chart
9. Count lamp flashes for initialization sequence. The flash code sequence begins with an initialization sequence which represents Code 12.
^ Wait for the first digit of the code initialization. The lamp will flash on for approximately one second. This flash represents a 1. The lamp will pause (remain off) for approximately one second after flashing the first digit. It will then flash the second digit of the trouble code.
^ When the lamp turns off, wait for the second digit of the code initialization. The lamp will quickly flash twice. These flashes represent the digit 2.
^ This lamp sequence or Code 12 will repeat two more times. Code 12 is not a diagnostic code associated with an ABS/TCS fault.
^ After Code 12 has been displayed three times, diagnostic code readout will begin. If no codes are stored. the readout of the Code 12 initialization sequence will begin again The display of only Code 12, indicates no ABS/TCS codes are stored by the EBCM.
10. Count lamp flashes for any stored codes.
^ When the initialization Code 12 has finished, any stored codes will then be displayed. Codes consist of lamp flashes which correspond to a two-digit trouble code.
^ The stored code will also be displayed three times.
^ For example, a Code 21, Right Front Speed Sensor Fault, will be displayed as two lamp flashes, a one second delay and then one flash. This code sequence will be displayed three times.
^ Once codes have been read out, the flash sequence will begin again starting with the Code 12 initialization sequence. Codes will continue to flash until the ALDL jumper has been removed.
^ Use the second illustration as a reference. Code 21 is shown as an example.
11. Record the trouble code.
12. Exiting Service Mode.
After interpreting ABS/TCS diagnostic codes, remove the ALDL jumper and exit Service Mode by depressing the RESET button. This will return the computer system to normal operation.
13. Return to the appropriate diagnostic procedure.
History and Current ABS/TCS Codes
The trouble code stored by the EBCM is not specifically designated as CURRENT or HISTORY. The ANTILOCK DISABLED message, however, may be used to assist in differentiating between current or history codes in the following manner:
^ If the message is on before entering diagnostic mode, the code is a current code.
^ If the message is off before entering diagnostic mode, the code is a history code.