On-Board Diagnostic Operation

ON-BOARD DIAGNOSTIC OPERATION

Diagnostic Trouble Codes (DTCs)
Diagnostic Trouble Codes (DTCs), when set, indicate that the IPC has detected a malfunction in a particular circuit or other system. Other system malfunctions are generally, but not exclusively, reported to the IPC via Class 2 data message. The IPC is programmed with routines for intemal checks that it follows only under prescribed conditions (called Test Conditions). When these conditions exist, the IPC checks certain circuits or systems for a malfunction. These checks are called failure conditions. When the failure conditions are true, a DTC is set. Some DTCs alert the driver through a Driver Information Center (Driver Information Center) message. Other DTCs don't trigger a driver warning.

Diagnostic Trouble Codes are not stored in the IPC's FEPROM and therefore will not be retained after a battery disconnect, either from the vehicle or just the IPC.

CURRENT DTC:
When the IPC determines that the test conditions and failure conditions for a particular DTC are true, it sets that DTC as 'Current.' All DTCs remain current at least until the next time the IPC fmds the test conditions are true and the failure conditions are false. A few DTCs remain current until the next ignition cycle or until the failure conditions are false several trmes.

HISTORY DTC:
After a DTC has been set, the IPC continues to monitor for the test and failure conditions. For most DTCs, if the test conditions are true and the failure conditions are false, the DTC is changed to history. some DTCs require the test conditions to be true and failure conditions false several times or require an ignition cycle to change from current to history. If there are no current DTCs for a period of 50 ignition cycles, all history DTCs will be cleared.

DIAGNOSTIC TROUBLE CODE (DTC) DIAGNOSIS
This section uses diagnostic charts, wiring diagrams and descriptive text to direct you in performing specific tests to locate and repair the problem. The diagnostic chart is a step by step procedure to determine the circuit or component that is the source of the problem. The wiring diagrarns and text describing the system, test conditions, failure conditions and actions taken when a DTC is set are located on the page facing the diagnostic chart. Refer to "PC Diagnosis Procedure' later in this section for details.

DIAGNOSTIC TROUBLE CODE DISPLAY
To display the DTCs, the ignition must be in the "ON" position. The "OFF" and "WARMER" buttons of the Climate Control Center on digital IPCs, or the Climate Control Panel for Analog IPCs, are depressed until all the segments of the display are "ON". The Driver Information Center will display the DTCs in the following manner:
1. All DTCs set. Each DTC will be displayed along with its status, current or history.
2. The order of DTC display will be PCM, IPC, ACM, SDM, TCS, RSS, PZM , IRC, RFA, CCP and PHN (CCP and PHN will only appear on vehicles equipped with these options).
3. Depressing the FAN DOWN button will bypass DTC display.

IPC CLEAR CODES
The IPC clear codes option may be used to clear stored IPC DTCs. When selected, the IPC Clear Codes option immediately erases all DTCs stored up to that point, and the Driver Information Center to displays "IPC Codes Clear." Once a malfunction has been corrected, clear DTCs so that any future service work is not needlessly confused.

Many IPC DTCs have complex test and failure conditions. Therefore, simply clearing DTCs, exiting diagnostics and watching to see if the DTC sets again, may not indicate whether a malfunction has been corrected. To verify a repair after it is complete, you must look up the test conditions and duplicate those conditions.