Toyota Repair: SMT Toyota Mr2 Spyder Transmission Issue

Question
Hi Ted,
I have just purchased a used ZZW30 Year 2000 mk. 3 mr2 spyder. It had only 30 000 kms on the clock and was used as a reserve car at a precision track driving school. It had an unknown service history.

The issue arises when travelling at a constant speed at around 2300 rpm in gear. The sequential warning light will turn on and i am unable to shift either up or down using the buttons on the wheel or the gearshift lever and will not register as being in neutral irrespective of the lever position. It stays in gear and still allows acceleration etc however when I come to a stop, the engine stalls and the engine warning light appears. It will not register as being in neutral until I remove the key from the igition and reinsert key. It then starts and runs as normal until it occurs again.

There are no gearbox noises or rattles. We took it to a Toyota dealer and had the synthetic transmission fluid changed and a diagnostic done.
The following codes were found.
P.1646 - transmission ecu malfunction
P.1646 - car communication malfunction
P.1882 - m/t code shift sensor malfunction
They cleared the codes also yet the problem persists
A 30000 km service was completed and no other issues were found
Grateful for any help you may be able to provide!
Callum

Answer
Hello, those codes indicate some major problems, as you can see, transmission ecu malfunction, will most likely need a new ecu and some other parts, the sequential shift transmission was nothing but trouble and very expensive to fix if something goes wrong, Toyota fixed many under warranty and this is why they stopped using this complicated shifting system, so be prepared to spend a lot of money to get this done, it may just be the ECU but there are other components and sensors involved not to mention the overcomplicated actuator system that can be affected. You can easily tie up $4,000 or so and parts may be hard to get.