Not sure if this problem would apply to "regular" H3's since mine has been highly modified with the LS3 conversion (see other thread) but since it's still the same tranny here goes:

Couple of months back noticed the "D" light would sometimes blink on and off while driving. At first I thought the transmission computer was blinking some kind of error code but it was not making much sense and didn't do it consistently. After a few weeks it started more frequently and I noticed it would blink whenever I turned the steering wheel to the left. That was very odd and I was thinking it had to do with a wheel speed sensor or something. A little further on it started downshifting to "3" and the "3" light would come on when I turned to the left (we are talking about a very slight left turn as in lane changing). After a bit of messing with it I finally determined that it was not the left turn that was causing this but the shift in the center of gravity. If I would drive on a shoulder with the body leaning right it would do the same thing. Then I look for a bundle of wires or something else under the car that's swinging to the right and causing a connection to break but can't find anything.

Anyone have any ideas??

 

Yaw sensor is on steering colum isn’t it? Or is it under driver seat.

 

I did not know there was a yaw sensor. What is the purpose of it and do you have an idea as to how it would be affecting the transmission?

 

Is the transmission fluid full? Is it possible to park on a grade and simulate the problem? Check for transmission codes while it is acting up. Next I would wiggle some wire looms. Under the dash and around the transmission. There might be some wires rubbing on an improperly mounted loom after your swap. Sounds like an unusual problem and might be difficult to pinpoint it. Might even be a faulty transmission range sensor or a selector cable failing or out of adjustment.

 

I forgot to update this thread. We did finally fix that blinking D light by replacing the shifter cable. I can't see how that was the problem but I can't argue with success...