Initial Inspection and Diagnostic Overview

Always begin by reading the diagnostic trouble codes (DTC's) using the DRB or scan tool. This procedure begins with Test 1A-Entering Diagnostic Tests. This test 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 CCD bus bias or communication problem, trouble codes will not be accessible until the problem is fixed. The DRB or scan tool will display an appropriate message. The following is a possible list of causes for a bus problem:
- open or short to ground/battery in either or both CCD bus wires (pins 4 and 43)
- open or short to ground/battery in either or both TCM bias wires
- open or short to ground/battery in the diagnostic connector bus wires
- internal failure of any module or component on the bus

NOTE: The CCD bus should have 2.5 volts (+2.5 volts on CCD+ and -2.5 volts on CCD-)

For more detailed information about diagnosing CCD bus problems, refer to the appropriate Body Control Module Diagnostic Procedure.

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 to diagnose an individual code. In certain test procedures, 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 (DRBII or equivalent) is required to extinguish the MIL.

Hard Code
Any Diagnostic trouble codes that comes back within three OBDII trips is a "hard" code. This means that the problem is there every time the TCM checks that circuit or function.

Intermittent Code
A diagnostic trouble code that is not there every time the TCM checks the circuit or function is an "intermittent" code. Some intermittent codes, such as 12, 14, 15, 18, 19, 21-29, 41-44, 48, 56-58, 70, and 74, are caused by wiring or connector problems. However intermittent codes 50-54 are usually caused by intermittent hydraulic seal leakage in the clutch and/or accumulator circuits. Problems that come and go like this are the most difficult to diagnose, they must be looked for under the specific conditions that cause them.

Reset Counter
For the most recent code (Code 1), the reset counter counts the number of times the vehicle has started since it was last set. The reset counter will count up to 255 starts.

When there are no diagnostic trouble codes stored in memory, the DRB or scan tool will display "NO CODES FOUND" and the reset counter will show "RESET COUNT = XXX".

The number of starts helps determine if the diagnostic trouble code is hard or intermittent.
- If the reset count is less than 3, the code is a hard code.
- If the reset count is greater than 3, it is considered an intermittent code. This means that the engine has been started most of the time without the code recurring.

Trouble Code Erasure
A Diagnostic trouble code will be cleared from TCM memory if it has not reset for 50 warm-up cycles.

A warm-up cycle is defined by CARB as "sufficient vehicle operation such that the coolant temperature has risen by at least 40°F from engine starting and reaches a minimum temperature of 160°F.

The Malfunction Indicator Lamp (MIL) will turn off after 3 good trips or when the DTC's are cleared from the TCM.