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-   -   AT light on when cold, codes U0101 P0745 U0073 (http://forum.mazda6club.com/atx-transmission-discussion/289969-light-when-cold-codes-u0101-p0745-u0073.html)

jpnsco 01-23-2014 01:58 AM

AT light on when cold, codes U0101 P0745 U0073
 
2003 Mazda 6, 2.3L, 138k miles

When starting it in the morning, the AT light is on and it jumps when putting it in R.

Turning it off and back on usually clears the AT light and it drives fine.

No CEL or other lights are on.

Mechanic reported an open circuit in the wiring harness going into the Trans, and gave me the following codes:
U0101 - Lost Communication With the TCM
P0745 - EPC Circuit Fail
U0073 - CAN Communication Bus Fail (web search shows diff description)

Taking it to a Transmission shop tomorrow and will report back.

Final Impact 01-23-2014 11:04 AM

Good luck at the shop as it may not be a trans issue. The 101 and 73 indicate a serious lack of communication between the on board computers in your vehicle (there are like 12). Its in limp mode when that happens. The 745 is likely after the fact as in limp mode the TCM controller jacks up the line pressure so you can do 3rd gear starts and not instantly burn up the drive clutches.

I'd disconnect the battery and unplug and inspect ALL MAJOR COMPONENTS!
I.e. ECM to BCM, TCM, DASH, ABS, etc. You're looking for corrosion, burns, pushed pins, opens, anything. And frankly because its mostly OK, simply reseating the "suspect connector" will likely fix the issue.

Q? is the interior glass holding moisture - is the car damp inside? What are the temperatures in your area? Does it go away when the car warms up and is driven for say 15min?

jpnsco 01-24-2014 05:45 PM

Thank you for the reply.

Shop is saying it's a bad solenoid inside the transmission and quoting $675 to replace it.

I did give it the once over but didn't see anything obviously wrong.

Haven't noticed moisture inside, and it spends most of its time around San Jose, CA. Temps are not that cold and it's been super dry lately.

I started it Monday morning (AT light was on and it jerked shifting into R), drove 1 mile, then turned it off and back on - AT light was off and it shifted fine.

Not enough time (or expertise) to handle it myself so will just let the shop do the repair then report back here with the results in case it helps someone else.

Thanks again.

chyno 02-24-2014 05:32 PM

i have the same cel on my i got the p0745,u0101,u0155,and u0100 and.im tryin what to ...i looked up.the p0745 and they.say i should.do a.tranmission flush only of the oil dirty good.luck report back please asap

Final Impact 02-24-2014 06:06 PM

Others have fixed problems by unfastening and reseating the connections I mentioned above. It is a valid fix.
Looking at the connections without unplugging them will not help the communication errors. Good luck.. .. ..

dagerm89 02-24-2014 06:41 PM

Quote:

Originally Posted by chyno (Post 3879058)
i have the same cel on my i got the p0745,u0101,u0155,and u0100 and.im tryin what to ...i looked up.the p0745 and they.say i should.do a.tranmission flush only of the oil dirty good.luck report back please asap

To echo FinalImpact, check and try reconnecting the connections he talked about. These codes have to do with communication and circuits so it's likely an electrical problem.

The workshop manual for the Mazda 6 doesn't mention anything to do with transmission fluid in regard to these issues so doing a flush probably won't fix anything. It never hurts to inspect your fluid though.

jpnsco 03-22-2014 04:14 PM

Reporting back... Shop said it was a failing Pressure Control Solenoid. Replaced that (p/n 48431) and a few other parts and it's been running/shifting great since. $688.01 out the door.

dagerm89 03-22-2014 07:38 PM

Quote:

Originally Posted by jpnsco (Post 3935609)
Reporting back... Shop said it was a failing Pressure Control Solenoid. Replaced that (p/n 48431) and a few other parts and it's been running/shifting great since. $688.01 out the door.

Ouch. Glad you're up and running though.

Final Impact 03-22-2014 10:48 PM

Quote:

Originally Posted by jpnsco (Post 3935609)
Reporting back... Shop said it was a failing Pressure Control Solenoid. Replaced that (p/n 48431) and a few other parts and it's been running/shifting great since. $688.01 out the door.

I echo this comment below!

Quote:

Originally Posted by dagerm89 (Post 3935857)
Ouch. Glad you're up and running though.


FWIW: A solenoid can not produce a CAN BUS error. However, simply unplugging the TCM from the harness could fix the error but NOT the solenoid issue.

Q? Are you sure those were not "stored errors" perhaps after emission testing or something like that? As in maybe they happened at different times and were NEVER RELATED???


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