No communication from computer to transmission

[StaceH]

I'm so frustrated with my 2008 Mazda 5 right now! Any ideas would be appreciated.
One day out of nowhere the car's AT and engine light turned on and the car locked into fail safe mode. (only drove in 3rd gear) It would flip in and out of this mode periodically. Since I saw the AT light I took it to a transmission guy. He pulled the codes that said the transmission was not communicating with the cars computer but that there was nothing wrong with the transmission. He said to get the computer reflashed ($100) and see if that worked. Took it to the dealer got it reflashed and nothing changed (notcool)
The Mazda dealer said for $50 more they would run a full computer diagnostic so we paid them for that but since the computer wasn't communicating they couldn't really run it or learn anything (and yes they still charged us again.) They said their best GUESS was the TCM (transmission control module) and that for $900 they would be willing to change it and see IF it helped. We didn't like the $900 IF so we took it elsewhere and put in a new TCM for $300. After the new TCM went in the car shifted fine but still had the AT and engine lights on so we were told once again to try reflashing the computer.
Took it to a different Mazda dealer who attempted the reflash but because the TCM and PCM were not communicating with each other it could not be reset or reflashed so they charged us for the reflash anyway and said your van still doesn't work but we have to charge you $100 for that 20 freaking minutes it took us to try reflashing the computer... SO ANNOYING!
We took it back to the guy who replaced the TCM to look at it again but I don't think he knows what to do next.
HELP!

 

[Indelibility]

Sounds like you have a bad Turbine Speed Sensor, It might also be an issue with the Shift Solenoid.

 

[markuszoom5]

If you can, take it to the dealer and trade it in, let somebody else figure it out, hopefully they don't test drive it, as a dealer near me does not care. I still have my 2010 Mazda5 and believe in it strongly, until something like this happens, hopefully not. Then I will trade it in and hate everything Mazda, like I hate VW now. But we shall see. Shame that the dealer cannot fix it, big shame...to me they are nothing but uneducated losers. What are you supposed to do? Give them a blank check? It looks like you already paid over $500, that's a luxury car payment.

 

[rodslinger]

Usually the simplest explanation to an issue is the correct one. Did anyone just check the CAN signal wire, power or ground wire running to the TCM or between the TCM and ECM if it has an intermittent open? Check continuity from end to end while wiggling the plug and the wire harness. That should have been ruled out first before all this other work.

And I'm not sure the dealership or a transmission shop is your best bet for this. I find dealerships aren't very capable at diagnosing anything that isn't on a TSB or obviously falling off in front of them. Transmission shops aren't good electrical shops either. Find a good, competent general repair shop that has some strengths in real troubleshooting.

 

[prrowe00]

Had the same problem, computers not communicating. Dealer found a pressure switch code also and so I changed that. Still didn't help. I got a used computer off a 09 and cleaned the wiring contacts really well and made sure the wiring harness had no stress at all on it. I haven't had the problem since. Crossing my fingers.