Mazda 626
4 cyl
107k miles

2 years ago I had a rebuilt transmission installed. About a year later, of coarse after the 1 year warranty In cold days sometimes it takes a little time to get moving. For the most part the car ran good for a long while until last week. Ok here we go: I was driving on the highway and the transmission started to shift up and down bucking like i was getting hit from behind. It does it low or high speed. I took it back to the shop and of coarse when they test drove it and scan for codes they could not find anything wrong. Its intermitted! A friend of mine thinks it might be electronic control module that controls the transmission. Does anyone of any clue or guide me in the right direction. I really need this car, my kids are missing school.
Please help....

 

What year is the 626 pegt10? Auto transmissions in the 94 and later 626 are a bit prone to failure due to fluid overheating for lack of an external air to oil cooler.
Does the transmission operate normally outside of what sounds like shifting in and out of overdrive and 3rd gear?
One thing I have run accross in the past with Mazda transmissions shifting in and out of overdrive at random times is a faulty Trans Fluid Temperature Sensor. In most Mazda transmissions, overdrive gear is disabled untill the fluid temperature reaches a certain point. If the sensor is reading a normal temperature and allowing overdrive and then suddenly sends a very low temp signal to the computer, the computer will shift back into 3rd gear untill the sensor is sending a good temp reading again. If the shop can get the concern to duplicate then have them monitor the fluid temp sensor voltage for correct signal.
A fault code often will not be set because the fluid temp is still within a possible range. Computer is just not programmed to recognize that a fluid temp signal change from 200'F to -10'F in an instant is not out of the ordinary.[:@]

 

I too have had a rebuild on an 02 626. It often shifts a little wierd, and hard. As the previous poster, it is now out of warranty. While doing a little disassembly today to cahnge the fuel filter...I discovered what I had already thought to be true. This thing has a Ford transmission. The same thing they used in the Probe if I am not mistaken. I also read that the Tranny is to small for the engine, and prone to failure. I don know what all year models this affects, but it doesn't appear to be good. Someone told me that the transmission shift sensor could be at fault. They also told me that it is located inside the transmission. Is this true?

At the same time I noticed a part on top of the tranny (I had the whole air intake removed atm). It had a Ford logo. It also had a alignment mark on it (like someone tried to mark the position before they removed it). The mark, and a couple of part specific marks seems to be outta wack. The #s on the part were YL8P 7F293 AA. I gotta wild hair up my butt to align the marks and see what happens...ne one know what I'm lookin at?

 

I really think this is the 1st auto transmission I have ever seen that doesn't have some hoses running to the radiator to cool the trans fluid. I stood there with my mouth hanging open looking to draw flies for quite sometime. It does , however, have a trans fluid overflow line that spills out near the battery (and typically ends up on my garage floor).