Mazda 3 repeat pcm failure
Good morning all
vehicle came in a few weeks ago with a customer complaint of a/c wasn’t cold, engine was revving up on its own with little to no throttle response and rough running. Towed in
we found a po606 and p2107. My tech determined the cause was a bad pcm and I agreed as ive seen this before. We replaced the pcm and programmed . Used a brand new pcm from the dealer. All was well in the world and we sent her on her way.
Vehicle just came back on hook One week later. Lady said Car would not start this morning. Tow truck driver said I jumped it and it fired up. He unloads it as he pulls it into my lot it starts running rough again with same symptoms and now the same codes as before. Once again the disgnostic chart leads me right to another bad pcm.
Not sure what to do from here. Anyone have any ideas?
Mike Becker has recently posted an insightful video about chasing ETC codes: youtube.com/watch?v=WnjTe7… Your situation is likely to be different (not the same car brand), but many testing principles should still apply.
I have seen acid-intrusion in the harness , from a previously leakomg-battery. It manifested itself as a throttle fault/default. This occurred because the acid created continuity between the high-frequency throttle-drive circuit and the TPS signal circuit. A continuit-check of the circuits revealed NOTHING however with the circuits active, I could see the drive-circuit activity on the TPS…
interesting are guys thinking I should chace the etc code and ignore the pcm internal error code at this time ?
Oh no, I’m not saying that....I just offered you something from my own experience, is all👍
Yes, ignore your 606 code. Most times those are set be poor power to the PCM, or intermittent power to the PCM. Start scoping the powers and grounds to the PCM while wiggling things. Most likely you have a poor connection somewhere and when you put in the first PCM, you fixered it for a while.
Definitely, I'd want to look into that TAC DTC before the PCM DTC. "Garbage in garbage out", as the PC programmers say.
The acid issue I have experienced on a Ford edge. It corrupted the TP reading as well. Spraying the harness with battery terminal cleaner, the kind that changes color, showed it was acidic. Thoroughly washing it helped, but it did not resolve. The harness was replaced at that point and the issue subsided.
Brandon is correct. My experience although not as much as Brandons is that about 50% of any type of internal module failure or performance code actually has nothing to do with the a PCM. It can be caused by low battery voltage , bad powers or grounds to the PCM. The PCM can only diagnose what it's been programmed to diagnose. If it gets"confused" for lack of a better term any thing is possible…
I dont know if it relates , I have had bad coils back feeding causing the 60X codes on Fords a few times, dont know if this is a possibility ?
Do a drag/tension test on the female terminals on the pcm connectors, especially those related to the throttle body. I have found that before on 2 different Mazdas. You will notice certain terminals noticeably loose compaired to others. See if you can duplicate the tb codes by wiggling or twisting the pcm connectors while the engine is running. Good luck.