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Discussion Starter · #1 · (Edited)
I've got a 2010 Mazda 3, 2.0 w/ 5 speed automatic, 125k miles. Suddenly the car was jumping around gears, when I put it into "manual mode", it was blank where it typically shows what gear you are in. I was also able to bounce the revs up and down like it was in neutral, but while maintaining a steady speed (this was while going uphill too). Now it's gotten worse, and it seems to be stuck in what feels like second gear and will not engage reverse. I am able to move the gear shift into all positions with no issues, it's like the transmission is not shifting. I just did a full transmission fluid flush and put in a new filter, and also replaced the TCM, just the issues still persist. Could this be the Shift Solenoid B sticking? The transmission fluid was pretty bad, so it wouldn't surprise me if it was stuck, but to me that doesn't explain why the gears are not showing when I shift it to manual.

My other thoughts were if the computer that I put in is bad as well, I did buy it from a shop that pulled it off another mazda 3 on their lot, all numbers did match on the two computers. My other thought is it could be a bad Transmission Position Sensor.

Edit for some testing I did:
  • Hooked up a code scanner, and I get U0101 Lost communication with Transmission Control Module PERMANENT
  • Shift Solenoid B is getting 5v when the car is put in drive, so the TCM is working for that part.
  • I checked the resistance on Shift Solenoid B and got 2.5 ohms, so it is good.
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