Transmission Control Systems: Description and Operation: Diagnostic Trouble Codes: Overview

The TCM continuously monitors system performance. When a problem is detected in the electrical control or hydraulic portion of the system, the TCM stores a Diagnostic Trouble Code. Most DTCs cause the transaxle to enter limp-in or default mode (see Default Desensitization). With the DRB6 Scan Tool in the Transmission portion of the diagnostic problem, it constantly monitors the transmission control module to see if the system is in limp-in mode. If the transaxle is in limp-in, the DRB6 will flash the red LED.
Always begin by performing a visual inspection and then read the diagnostic trouble codes (DTC's) using the DRB scan tool.
The DRB6 will direct you to the specific test(s) that must be performed. If more than 1 code exists, diagnostic priority should be given to the most recent code.
If there is a BUS communication problem, trouble codes will not be accessible until the problem is fixed. The DRB will display an appropriate message. The following is a possible list of causes for a bus problem:
- open a short to ground/battery in the PCI bus wire pin 43
- internal failure of any module or component on the bus

NOTE: THE PCI BUS SHOULD HAVE ABOVE 0.6 VOLTS WITH THE IGNITION ON, HEADLAMPS ON AND ALL DOORS OPEN.

For more detailed information about diagnosing PCI bus problems, refer to Powertrain Management. The bus error message displayed by the DRB should be helpful in diagnosing the PCI bus.
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. In certain test procedures within this book, codes are used as a diagnostic tool.
DTC's which affect vehicle emissions will illuminate the Malfunction Indicator Lamp (MIL). Although these DTC's will be stored in the TCM immediately, it may take up to five minutes of accumulated trouble confirmation to illuminate the MIL. Three consecutive successful OBDII trips or clearing the DTC's with a diagnostic tool (DRBIII or equivalent) is required to extinguish the MIL.