I recently swapped out my 1996 Auto trans. For a 5 Speed out of a 1995 with a blown Motor. I had the motor rebuilt at the same time as well as all the seals in the manual at that time. I installed an ECU from a 1997. I removed the Auto trans computer as well. Now, I have a check engine light that won't go out and it says that I have an ECU - TCU communication error? (I didn't change the wiring harness) I'm not sure what else needs to be connected? If someone can send me in the right direction, it would be great! Thanks in advance.

 

The ECU and ALL of the other sensors need to talk to each other. Is the new ECU from an automatic car?

The TCU is the Transmission Control Unit, used only on automatic cars.

Look at the Wikipedia link Transmission control unit - Wikipedia, the free encyclopedia for a starting point.

You have a 1996 automatic transmission wiring harness, a 1995 manual transmission. and a 1997 ECU. With all of the emissions changes (different sensors, different programming) that have happened over those years, you may have an interesting task ahead of you. You know that, right!

Consider discussing this with a Miata specialist mechanic. I doubt any of the Mazda publications (Workshop Manuals will help directly.). You could start by comparing part numbers from the various year Manuals. I suspect the parts all need to be capable of talking to each other.

If you don't have a shop nearby, a call to Flyin Miata may provide some guidance.

Do you need to pass an electronic (OBDI or OBDII) emissions in your area, in other words is the check engine light a concern or simply an annoyance?

 

Hey Charles, the ECU is from a 5 Speed. I was under the impression that the 96 & 97 were identical in electronics. My biggest question really is how does an ECU from a 5 speed know the the transmission communication isn't right when the TCU isn't even there? I'm fairly certain that I'm just needing to make a connection between a few wires but not sure which ones? As for the check engine light, it is part of the registration process here in Utah. So I'm pretty much dead in the water.
Thanks Ali

 

We have all of the wiring diagrams right here on the forum.

I'm not sure why you are seeing the code. Yes, '96 and '97 were the same. I can't tell you functionally if it will make an operational difference or not. It may cause the computer to remain open loop during driving.

Study the diagrams for clues as to why.

 

As I understand it, you still have the 1996 auto trans wiring harness. Check to see if there are any connectors that go to the auto transmission. if so, it is likely that the ecu expects to see a resistance from those connectors, or possibly a voltage, either of which you may need to supply. As sixshooter suggests, compare the two wiring harnesses....perhaps a connector can simply be deleted.

 

Ok. I'll try to look at the diagram and track down which wires are different. Thanks for the info. 😊