The TCM receives inputs, processes information and actuates the output elements to provide optimal shift points. See Fig 1 . The TCM is programmed for maximum shift comfort and fuel economy. The TCM on most BMW vehicles is located in the E-Box next to the ECM (DME). There are several types of TCM housings:

35 Pin TCM (TCU) - used on the 4HP transmissions.
55 Pin TCM - used on the A4S310R (THM-R1).
88 Pin TCM - used on all others up to 1998.
134 Pin TCM - used on all BMW transmission from the 1999 model year. (Note- the 134 pin TCM was introduced on the 1998 Models equipped with the A5S440Z).

Fig 1: Electrical System Components
Courtesy of BMW OF NORTH AMERICA, INC.

The 134 Pin TCM is also referred to as SKE (Standard Shell Construction). The SKE housing uses 5 separate connectors. On transmission applications only three connectors 1, 3 and 4) are used. Connectors 2 and 5 are blank and are NOT used. The connectors are blue in color to avoid confusion with the ECM (DME) connectors which are black. See Fig 2 .

Fig 2: Identifying Transmission Control Module & Connectors

Courtesy of BMW OF NORTH AMERICA, INC.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Transmission Control Module

Use the Manual With the Right Hardware

When to See a Mechanic

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