General

DIAGNOSTIC TROUBLE CODES

Diagnostic trouble codes (DTC's) are codes stored by the Transmission Control Module (TCM) and the Transfer Case Control Module (TCCM) that help us diagnose Transmission or Electronic Transfer Case problems. They are viewed using the DRBIII(R) scan tool.

Always begin by performing a visual inspection of the wiring, connectors, cooler lines, transfer case 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 or transfer case problem. Ensure that the engine is running properly and that no PCM DTC's are present that could cause a transmission or transfer case complaint.

If there is a communication bus problem, DTCs will not be accessible until the problem is fixed. The DRBIII(R) will display an appropriate message. The following is a possible list of causes for a bus problem:

Open or short to ground/battery in any of the bus circuits.

Internal failure of any module or component on the bus

Each Diagnostic Trouble Code (DTC) is diagnosed by following a specific testing sequence. The diagnostic test procedures contain step-by-step instructions for determining the cause of a Transmission or an Electronic Transfer Case DTC. Possible sources of a DTC are checked and eliminated one by one. It is not necessary to perform all of the tests in this book to diagnose an individual DTC. These tests are based on the problem being present at the time that the test is run.

If the TCM 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 DTC's will be stored in the TCM immediately as a 1-trip failure, it may take up to five minutes of accumulated trouble confirmation to set the DTC and illuminate the MIL. Three consecutive successful OBD II trips or clearing the DTC's with a diagnostic tool (DRBIII(R) or equivalent) is required to extinguish the MIL. When the TCM requests that the PCM illuminate the MIL, the PCM sets a DTC ($89) to alert the technician that there are DTC's in the TCM. This must also be erased in the PCM in order to extinguish the MIL.