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2009 Mazda 3 2.0l replaced PCM after P0758, worked for a while and code came back with new PCM

2284 Views 25 Replies 3 Participants Last post by  dkeruza
So my son's Mazda 3 started throwing code P0758, transmission was on limp mode. I cleared the codes, and nothing, as soon as I put the car into D, codes came back.
I research a little online and most of the people pointed to the TCM module being bad. These 2.0l cars don't have a TCM, the tranny is controlled by the PCM.
Before I went ahead and ordered a replacement PCM I performed a wire continuity test from the PCM plug to the Plug in the transmission, test passed, then I checked the resistance of the solenoids, and the test passed, then I supplied 5V to the solenoids and I could hear the solenoids click, so the test passed.
I ended up ordering a re manufactured PCM and after dealing win the damn PATS (My son only has 1 key) I was able to start the car. Codes were gone, and car was shifting perfect in the driveway. I took it for a test drive, and everything was good.
My son left, and 20 minutes later, he called me and said that the car is doing the same thing again. Transmission in limp mode, AT and MIL lights on.
I still have to pull the codes to make sure the code is be the same. But I am pretty sure it will be.

My question is, can a "faulty" solenoid keep blow one of the lines in the PCM? Or could be something else?

What I am thinking is that the solenoid might get "shorted" maybe intermittently and blow the PCM line?
Should I replace the solenoid before playing with a new PCM?

There is nothing else in between the PCM and the solenoid to be causing this issue. Just the wires.

Any suggestion will be appreciated.
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I have a question before I mess up putting the valve body back in the transmission.
The rod that I marked with the red circle in the 1st picture should go inside the part I marked with the red circle in the 2nd pic, right?


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Thanks. Seems like it's kind of shown in page 50. But still, not super clear. Anyway, common sense says that it goes where I pointed in my pics. Its the only way that the rod in the valve body will move mechanically.
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I just want to say that the problem is fixed. New pan, new harness, new computer and car is good to go.
I wanted to say thanks to @Akmnhg5A for all the help and support.
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Congratulations! It just feels great to be successful after the journey of discovery and your own hard work.
Yes it does.
I hope my experience will help someone else down the road.
21 - 26 of 26 Posts