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Automatic transmission.jpg

Most ecomodders would not buy a new car that has an automatic transmission but many people prefer an auto or already have a car that is an auto. In many automatic cars the ECU controls the gear that the transmission is in at any time. People with an automatic transmission can make their car more efficient by manually controlling the gear the car is in making the car shift earlier when accelerating.

This modification is easier than changing out an automatic for a manual transmission.

Car makers introduced this type of transmissions in the final decade of the 20th century. Different car manufacturers have been using a variety of labels for their manumatic transmissions, such as 'tiptronic', 'Geartronic', 'Touchshift', 'Sporttronic', and others.

Performing this modification with the torque converter lock up mod will bring the transmission efficiency much closer to that of a manual.
This modification may not work well if the torque converter remains ECU controlled.

Note: Some of the very new automatic transmissions have been reported to have the same efficiency as manuals.

Thread for discussion on this wiki page


Instructions for mod

This modification involves taking control of the signals between the ECU and the transmission. There are likely to be 3 solenoids to be controlled depending on how many gears are available.
- An overdrive gear which in most conditions should likely be engaged
- 2 solenoids that work with each other to select the actual gear

Consult a wiring diagram or workshop manual for initial information about electrical connections to the automatic transmission.

Many work shop manuals and wiring diagrams will not have detail about the connections to the automatic transmission and it is very unlikely to detail the voltage levels required for each gear selection. When the transmission solenoid signal wires and voltage levels for each gear can't be found from documentation, perform the following steps to locate the signal wires

Diagnostic LED

- Locate the automatic transmission
- Identify all control wires that are connected to the transmission. The wires of interest are likely grouped together on one connector
- Cut a small section of the insulation away from each of the wire.
- For each of the wires solder a wire to the location where insulation was just cut away. Ensure the new soldered wire is long enough to extend into the cabin of the car
- Solder a LED and resistor in series to each of the new wires in the cabin. Connect the other side of the resistor plus LED to 0v which is the most exposed metal in the cabin
- Take the car for a drive. If the correct wires have been found the driver will see the LEDs light up in a particular arrangement for each gear selected. If the LED states do not correlate with any shift changes locate different wires from the transmission and repeat. Note: there can be up to a few second delay between signals changing to a shift change
- Note down the states of each LED in each gear configuration so that you know the control signals required for each gear when connecting the manual switch.

Performing the modification
The following modification assumes that the signals found are similar to the signals shown in the following table

Gear Selection Gear Select Signal Wire 1 Gear Select Signal Wire 2 Over Drive Signal
Reverse 1st 0V 12V 12V
Neutral Irrelevant Irrelevant Irrelevant
Drive 1st 0V 12V 12V
Drive 2nd 12V 12V 12V
Drive 3rd 0V 0V 12V
Drive 4th 12V 0V 12V

Manual gear selection control

- Once the signal wires have been isolated trace them back to the closest location to the cabin which is likely at the ECU.
- Cut the signal wires and solder wires of the suitable gauge (thickness) and length to reach the desired mounting location.
- If the driver wants to be able to select between automatic and manual control a selection switch should be installed. Using a single pole double throw switch (2 position switch) connect the common terminals to the transmission side of the signal wire. Connect the other end of the signal wire (the ECU side) to one of the other switch terminals. The other terminal of the switch will be connected to the manual control signals.
- Using a 2 pole 4 (or above) throw linear or rotary switch, connect the 2 common terminals to the isolating switch or transmission signals. Connect the terminals which will be selected when rotating the switch so that it will give the required voltages for the transmission solenoids when the switch is at the appropriate gear selection
- Using a 2 pole single throw switch connect the overdrive signal to the isolating switch with common connected to the transmission side of the switch and the ECU side connected to one of the terminals. The other terminal would be connected to either 0 or 12v depending on the LED state observed for this signal when the transmission is in overdrive

This arrangement will allow the driver to select between the ECU controlled gear selection and manual gear selection

Note: Most cars will have an ECU which checks the load of the transmission solenoid signals therefore if the ECU "sees" an open circuit it will likely throw errors however the car will likely still work without any issues as long as manual gear selection is used for the remainder of the trip.
Note: Some cars may not have their automatic transmission controlled by the ECU.

User experiences

Please enter your user name and any relevant data in the table

User data
User Name Car Make, Model, Year Cost of Mod Time to Perform Mod MPG Before Mod MPG After Mod MPG improvement guess Instruction Link
Saand Mazda, 626, 1991 $5 4 Hour Only improvement likely if shifting causing lower RPMs

Problems / Consequences of mod

- Incorrect installation may cause poor gear control
- Going into manual gear control causes the ECU to go into an error mode, car will still drive however going back to automatic gear selection may not work well.
- Shifting into incorrect gears could cause damage to the transmission and the car to stall


Forum thread links

Freezing the Slushbox. Torque Converter on-demand lockup switch

External links

The Free Mod Series: Part VIII Electronic Transmission Controller - Toyota Forums :: Toyota Nation

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