Description of On-Board Diagnostics: Overview

DIAGNOSTIC TROUBLE CODES

Diagnostic trouble codes (DTCs) are codes stored by the PCM (NGC) or TCM (EATX) depending on the powertrain application and help diagnose Transmission problems. They are viewed using the DRBIII scan tool.

Always begin by performing a visual inspection of the wiring, connectors, cooler lines and the transmission. Any obvious wiring problems or leaks should be repaired prior to performing any diagnostic test procedures. Some engine driveability problems can be misinterpreted as a transmission problem. Ensure that the engine is running properly and no engine DTCs are present that could cause a transmission complaint.

If there is a bus communication problem, trouble codes will not be accessible until the bus problem is fixed. The DRBIII will display an appropriate message.
Each diagnostic trouble code is diagnosed by following a specific testing sequence. The diagnostic test procedures contain step-by-step instructions for determining the cause of a transmission diagnostic trouble code. Possible sources of the code are checked and eliminated one by one. It is not necessary to perform all of the tests in this book to diagnose an individual code. These tests are based on the problem being present at the time that the test is run.

All testing should be done with a fully charged battery
If the control module records a DTC that will adversely affect vehicle emissions, it will request (via the communication bus) that the PCM illuminate the Malfunction Indicator Lamp (MIL). Although these DTCs will be stored immediately as a 1 trip failure, it may take up to five minutes of accumulated trouble confirmation set the DTC and illuminate the MIL. Three consecutive successful OBDII (EURO STAGE III OBD) trips or clearing the DTCs with a diagnostic tool DRBIII or equivalent) is required to extinguish the MIL. When the Transmission Control system requests that the PCM illuminate the MIL, the PCM sets a DTC P0700 ($89) to alert the technician that there are DTCs in the Transmission Control System. You must also erase the DTC P0700 in the PCM, in order to extinguish the MIL.