- Description of On-Board Diagnostics

Diagnostic Flow Diagram:

Instrument Panel Cluster:

ON-BOARD DIAGNOSTICS SYSTEM OPERATION
This vehicle is equipped with an extensive on-board diagnostic system which is capable of detecting and compensating for faults, alerting the operator of a fault and recording pertinent data during the failure. It is also capable of displaying information about current vehicle performance when a fault occurred.

In order to access and control the self diagnostics features available, additional electronic components are utilized by the service technician. The Climate Control Center (CCC) and the Fuel Data Center (FDC) provide displays and keyboard switches.

The display and keyboard information is transmitted over a single wire data circuit which carries the coded data messages back and forth between the different control computers. and the display panels (CCC/FDC). This communications process allows the appropriate computer to transfer any of its available diagnostic information to the appropriate panel for display during service. By depressing appropriate buttons on the CCC, data messages are requested to be displayed on the FDC. the diagnostics mode, the mode indicators on the CCC are used to indicate system operating modes. The different modes of operation are indicated by the status indicator either being turned "ON" or turned "OFF".

OPERATING ON-BOARD DIAGNOSTIC SYSTEM
To enter diagnostic mode, proceed as follows:

1. Turn ignition "ON".
2. Depress the "OFF" and "WARMER" buttons on the CCC simultaneously and hold until the segment check appears on the Instrument Panel Cluster (IPC).

SEGMENT CHECK
The purpose of illuminating the IPC is to check that all segments of the LED displays are working. The turn signal indicators DO NOT light during this check. If any of the segments are inoperative, the affected display panel will need to be diagnosed.

TROUBLE CODE DISPLAY
After the segment check, any trouble code stored in computer memory will be displayed. Codes may be stored for the PCM, IPC, ACP, or SIR systems.

Each trouble code consists of the system abbreviation: (P: Engine, PCM) (I: IPC), (A: ACP), (R: SIR), (T: TCS), (S: RTD), a three digit code identifier, and the letter C or H. All codes for each system are displayed together, in the order of their three digit number (lowest first). The final digit of the code, a "C" or "H" is used to indicate whether the code is Current or History. A "C" means the fault was still present the last time the diagnostic test was run, while "H" means the failure was not present the last time the code was tested for.

If no codes are present for a system, a "NO X CODE" message (with "X" being the system i.e. E, I, A, R, T or S) will be displayed. If the communication line to a component is not operating, a "NO X DATA" message will be displayed, indicating that the IPC could not communicate with that system.

At any time during the display of trouble codes, if the "AUTO" button on the IPC is depressed the system will exit "Service Mode" and go back to normal vehicle operation.

PCM Status Lights:

STATUS LIGHTS
While in diagnostics, the displays on the CCC may be used to indicate the status of various inputs and operating conditions. The meaning of each word or symbol on the panel will change depending on whether the Air Conditioning Programer (ACP) or Powertrain Control Module (PCM) system level is selected.

SELECTING THE SYSTEM
After trouble codes have been displayed, a specific vehicle system (PCM, IPC, ACP, SIR, TCS, or RTD) may be selected for testing.

The first available system will be automatically displayed (i.e. PCM?). While selecting the system to test, any of the following actions may be taken:
1. Depressing the "HI" button on the CCC will select the displayed system for testing.
2. Depressing the "LO" button on the CCC will display the next available system selection. This allows the display to be stepped through all system choices. This list of systems can be repeated following the end of the system list.
3. Depressing the "OFF" button the CCC will stop the system selection process and return the display to the beginning of the trouble code sequence.

SELECTING THE TEST TYPE
Having selected a system, the first available test type will be displayed (i.e. PCM DATA?). While selecting a specific test type, any of the following actions may be taken:

1. Depressing the "HI" button on the CCC will select the displayed test type. At this point the first of several specific tests will appear.
2. Depressing the "LO" button on the CCC will display the next available test type for the selected system. This allows the display to be stepped through all available test type choices. This list of test types can be repeated following the display of the last test type.
3. Depressing the "OFF" button on the CCC will stop the test type selection process and return the display to the next available system selection.

DATA, INPUTS, OUTPUTS, OVERRIDES, CLEAR CODES or SNAPSHOT
^ Selection of the "DATA?", "INPUTS?", "OUTPUTS?", or "OVERRIDE?" test types will result in the first available test being displayed. Four characters of the display will contain a test code to identify the selection. The first two characters are letters which identify the system and test type (i.e. PD for PCM DATA) and the last two characters numerically identify the test (i.e. PD01 for Throttle Position).

While selecting a specific test, any of the following actions may be taken:

1. Depressing the "HI" button on the CCC will display the next larger test number for the selected test type. If this button is pressed with the highest test number displayed, the lowest test number will then appear.
2. Depressing the "LO" button on the CCC will display the next smaller test number for the selected test type. If this button is pressed with the lowest test number displayed, the highest test number will then appear.
3. Depressing the "OFF" button on the CCC will stop the test selection process and return the display to the next available test type for the selected system.
4. Depressing the "LO" button after override is displayed will put the system into "ECM CLEAR CODES?" display. Depressing "HI" or "LO" at this point will either clear codes or bypass code clearing.

^ Selection of "CLEAR CODES?" test will result in the message "CODES CLEARED" being displayed along with the selected systems name. This message will appear for 3 seconds and then return to the next available test type.

^ Selection of the "SNAPSHOT?" test type will allow the recall of all "DATA" and "INPUT" values for the selected system from a specific point in time. Those values may be retrieved for either a snapshot that was manually triggered, or if the selected system allows, a snapshot from the setting of a code.