Most car enthusiasts are pretty comfortable with the idea of rewriting
management software or adding electronic modules to alter control of the engine.
But electronic modification of auto transmissions? Uh-oh!
In this article we’ll introduce you to the world of aftermarket controllers
that are designed for use with late-model electronic-controlled automatic
But, first, let’s run through a quick run-down on how an auto transmission
Electronic-Controlled Transmissions –
How they Work...
The operating principles of automatic transmissions have remained essentially
unchanged for decades (with the exception of CVTs).
There are two main sections of an automatic transmission – the
hydraulically-controlled planetary gear unit and torque converter.
In older-style transmissions, the planetary gears are controlled by a valve
body which relies on changing fluid pressure. Fluid pressure is controlled
primarily on the basis of road speed and throttle position - this diagram shows
how these two variables oppose each other from opposite sides of a spool valve.
Movement of this spool valve directs fluid to a specific planetary gear control
clutch and/or band, so controlling gear changes. A separate
kickdown mechanism and P-R-N-D-L manual control valve are also necessary for
complete transmission operation.
The automatic transmission is mated to the engine using a fluid coupling
known as a torque converter. The engine drives an impeller to produce energy in
the hydraulic fluid while a turbine (connected to the transmission) converts
this hydraulic energy into mechanical force. When required, the torque converter
also allows a considerable amount of slip between the engine and transmission.
This allows the car to come to a stop without stalling and multiplies applied
torque when accelerating (because the engine can turn faster than the
transmission). The amount of torque converter slip varies at different rpm and,
unless there’s a lock-up mechanism, there will always be some degree of slip.
As early-generation electronic transmissions were introduced, it became
common to use electronic control for secondary functions - such as kickdown and
torque converter lock-up. The torque converter lock-up mechanism (aka torque
converter clutch) is used to improve engine efficiency and fuel consumption at
cruise. In this situation, the impeller and turbine sides of the torque
converter are locked together to eliminate slip.
Today, automatic transmissions have evolved further to incorporate full
electronic control. The vehicle’s transmission computer (which is now typically
integrated into the main ECU) controls a set of solenoids to control fluid
pressure and, as a result, gear change characteristics. Up to 14 inputs are used
to determine shift properties and sometimes six solenoids are controlled by the
transmission control unit. Note that hydraulics are still used to apply the
clutches and bands that trigger a gear change – the electronic part of the
system is used only for control.
Powertrain Control Solutions
Universal Transmission Controller
The Powertain Control Solutions (PCS) Universal Transmission Controller is a
highly sophisticated stand-alone aftermarket transmission computer.
The US-built PCS Controller is programmed using a Windows interface with the
availability of up to 16 digital inputs, six analogue inputs, two temperature
inputs and four speed inputs. In most instances, the controller is programmed on
the relationship between road speed, engine load, engine rpm and throttle
The PCS Transmission Controller offers programmable shift points, selectable
shift modes (power, towing and economy), six pulse-width modulated outputs, six
digital driver outputs (ideal for engaging a lock-up torque converter), four
frequency outputs (including one for speedometer drive) and a data logging
capability. It can also be configured to work with separately available
All electronic components in the PCS Controller are suitable for automotive
application and a weather-sealed plastic connector is built into the case. The
PCS Controller is claimed to control every type of electronic transmission from
Ford, Nissan, GM, Toyota , Mazda, Chrysler and many
other manufacturers. Note that the company is also interested in developing the
Controller to suit currently unsupported transmissions.
Cost is around US$700 plus the necessary wiring harness (which typically cost
or www.transmissioncontroller.com for
The Baumannator TCS electronic trans control is designed for use with the
Ford AOD-E/4R70W and E4OD transmission (as used in post ’98 light trucks and
Mustangs up to mid ‘90s). It is hoped that more transmissions will be supported
in the future.
Fitment of this stand-alone unit gives complete electronic transmission
control and allows you to install either of these Ford transmissions into custom
built vehicles. A throttle position sensor can be added when using the
Baumannator TCS behind a carby engine.
The micro-processor based controller is tuned via Windows-based software to
control shift pattern on the basis of road speed, throttle position and other
inputs. The line pressure curve (versus load) can also be tuned to improve the
torque capacity of the transmission and part-throttle shift firmness. Torque
converter clutch operation is also adjustable on the basis of throttle angle and
Two different sets of calibration data can be stored into the Baumannator to
give on-the-fly adjustment and there’s the option of sequential-style gear
operation using OE cruise control switches.
In addition to enabling fitment of the Ford AOD-E/4R70W and E4OD
transmissions into custom-built vehicles, the Baumannator can also be integrated
into the wiring loom of vehicles that are factory equipped with these trannies.
The system has a reputation for being very easy to wire and tune.
The system retails for US$425 or US$550 including harness.
Compushift is another US-based product that’s designed to control popular
Ford and GM transmissions. We believe that they support the GM 4L60/65
transmissions used in various Holden vehicles. The Compushift
is supplied with a harness and throttle position sensor to enable transmission
installation into any vehicle.
Designed by HGM Automotive Electronics, the Compushift uses a digital
processor that is delivered with predetermined programming. If required, simple
changes to the program can be made with screwdriver adjustment. There is no PC
or laptop interface.
The Compushift controls six shift solenoids and torque converter lock-up is
user-adjustable based on road speed, rpm or gear. A backlit LCD display
unit/programmer is also available as an option – this shows transmission
temperature, hydraulic pressure, gear position, torque converter lock-up and
throttle position. It also functions as tachometer, speedo, stopwatch and
The components are contained in a powder-coated aluminium box with mounting
flanges and features automatic protection against failed solenoids and
Cost is US$1185.
TCI Automotive TCU
Here’s another US-based stand-alone trans controller. At this stage, the TCU supports GM 4L60E and 4L80E transmissions with
the Ford products yet to come.
Using the TCU (Transmission Control Unit) and T-Com WP software, the user can
program line pressures, shift timing and shift firmness. Tuning is quick and
simple – initial calibration requires only basic information on tyre size, gear
ratio and transmission type. After this information is entered you’re ready to
program the shift data.
The TCU incorporates a waterproof case, complete wiring harness, T-Com WP
software, instructions and a laptop connection cable. Adapters are available for
fitment to carby engines.
Prices range up to around US$900 - visit http://www.tciauto.com/tci.htm
Stick around for Part Two (the final) of this series – there are a bunch of
other aftermarket controllers to check out!