I recently got a Mazda 5 given to me. It is having issues that I am thinking is the PCM module failing. Former owner stated it would drive along at 35 to 45 mph then it would flash the AT light and you would eat the dash (.as though some one were applying the brakes hard) i have not been able to duplicate this issue. It does shudder and flash AT light at 10 to 15 mph . Yesterday it down shifted at 65 from 5th to 3rd. Issue seems to be less if in manual mode, not totally gone. Also the check engine light along with the traction control light come on at same time. Inaddition the radiator fan and ac compressor were on when heater was on and set to 85 degrees. Computer has been setting following codes ,
U0101 Lost communication with transmission module
U1900-A0 ABS brake system receive error
No transmission codes
I had Auto zone pull codes and an independent shop that serviced car for former owner check also.

nice car otherwise but dont want to throw money away. Im.thinking the PCM IS FAILING. The climate issue with the ac compressor and radiator fan always on when heat is on is making me lean this way. Again this is the first mazda for me so the , ac ,radiator fan issue , could be normal or evidence the PCM starting to fail.
What do you think ?

cheers

 

Not uncommon for the TCM to fail in this age vehicle.

 

i went in and moved the TCM to the firewall .The troubles went away and only issue new, was a sometimrs hard shift into srcond. Well yesterday it dtarted throeing a AT light flash. Weird thing is that no hard codes , I checked last night with reader. Also whrn i shifted into manual mode the AT light came on for a few seconds solid.

I sm thinking that it may be a connection issue. Dirty or ?? When i relocated TCM I jad to remove batt box etc ehich included disconnecting the PCM. IM contemplating disconnecting the TCM snd reconnecting. Sll in all slot better just not 100% better yet. Cheers , thsnks for the replys and motor on

PS i hate these tiny keyboards on phones. Swolen fingers frow wrenching and being a carpenter make for interestingly sprllrd posts.

 

I would have carefully looked using a magnifying glass all the tiny connectors on the ECU/TECM harness connector before considering relocating it from the OEM location.
That relocation which I often read on the forums is a bad idea!
When we get any vehicle in the shop that the customer has done that or bought the vehicle with the previous owner remounting the ECU/TCM we have them sign a disclaimer waver.

 

Thank you ! We went for a 70 mile drive and not an issue. The hard 2nd gear shift calmed down . Time will tell. If its better , no issues i shall remount under battery box.

Thank you Callisto and all posters

 

Maybe also time to think about doing a pan and filter service on the transmission. This way you can see what is in the bottom of the pan and also attached to the magnet. You will also be able to see if there is accumulated varnish forming on the valve body.

Also if there is room you can place Theral protectors on the ECU/TCM.

 

First time on this Forum.
I have a 2011 Mazda 3i w/ 2.0 liter engine. Check engine light would come on for a while and then go off after a while. Tried to sneak it in for annual inspection when light was off and was failed for:

P0101: Mass or Volume Air Flow A Circuit Range / Performance
P0139: O2 Sensor 12 Circuit Slow Response
U0100: Lost Communication With ECM/PCA
U0101: Lost Communication With TCM
U0121: Lost Communication with Anti-Lock Brake System Ctrl Module

Car drove fine before that with no problems at all, only w/ check engine light on.
Shop unsure which module to replace first if it needs to be replaced.
Thanks for any information on this.











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Welcome to the forum

So to answer.....START OVER

First and this is very important for you to save money and also get the correct diagnosis.

Find a shop that has an ASE sig posted somewhere on the property.

Thank you for posting the DTC but they are at this point ancient history and cant really be used to help you.
Going and looking at each one is a total WASTE of time and worse if you are a DIY and not a trained Automotive Technician specifically a qualified Diagnostic Technician. Hence look for a shop with ASE because they should have at least a certified ASE working for them.
However, if you feel FROGGY look up me username and posting and you are sure to find one of several responses, I explain how to properly get the most current ECU, PCM,TCM information using a Grade Dianostic scanner that connect via a cable directly to the OBDII Diagnostic connector.


ASE






When any member is posting asking for help PLEASE include IMPORTANT information like the miles and transmission type with your response.

 

Now there is a new issue with the car. When rolling a stop sign, not a complete stop it is acting like it gets confused as to what gear is should be in, first or second. It hammers BAD AT light comes on and thrn goes off as I accelerate. No hardcode, light permanently on on dash. I dont know if it may be a bad.solrnoid or ?? As usual any and all input appreiaciated. Slowly getting better just not 100% yet, and.the same for the driver.

 

If I had not posted yet.... on at least this thread... you need to drop the pan and do a filter and pan fluid change. this way you can see what has settled in the pan as well the visual of the valve body for a varnish that may be causing shifting issues as the ones you are describing.

A failed solenoid would be stuck in gear or no shift into gear at all

Some minor mechanical problems like dirty valve body will not necessarily generate a DTC. NO vehicles ECU is that sophisticated yet form any auto manufacture. In fact by all accounts of where we are in the tech world they are really dinosaurs.

Case in point the often misused and understood phrase "ADAPTIVE" setting in any ECU. As if they are some minor AI computer. LOL