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Hey all, I've been lurking for a while but this is my first post, so thanks in advance to anyone who replies, and sorry for the length! I've got a 2007 Mazda 3 that a couple of weeks ago failed to start. It cranked but failed, and then eventually succeeded after 10 minutes or so, but the check engine light was on.

It was good for a week or so, with the CEL on for about half of that, when it happened again. Failed to start, got it started, and CEL on. I also noticed the engine stuttering, and almost stalled out when braking; this smoothed out over time. Same thing happened this week, brought it to the dealership, and was told PCM was fried somehow and would cost 4800 to replace PCM and wiring harness.

Now, I noticed that it had rained heavily the night before each of the failures, and am guessing moisture caused a short somewhere. That being the case, is it possible that the car should be safely driven when dry and it starts/runs fine? Would the car be considered safe to drive if the PCM is truly fried? Lastly, would it be possible to repair the short or cause of damaged PCM rather than replacing the entire wiring harness and PCM like the dealership indicated?

Thanks again!
 

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$4800 is ridiculous. The PCM might very well be damaged and can obviously be replaced. I have not priced them out, but I have priced the TCM (sub $500). Do you have a 2.0L with an all-in-one PCM/TCM or do you have the 2.3L with the separate modules? That might change the price.

I was looking at prices of wiring harnesses a year ago and if I remember they were in the $500 range. Having a new one without brittle wires and connectors would be sweet, especially when doing a project on an engine that involves taking connectors on and off.

Replacing the wiring harness would a pain, but it is doable as a DIY project. I would scrap a car before I paid nearly $5000 for a PCM and wiring harness. I had to remove the wiring harness and reinstall it when I did an engine swap.

If you drive your car the way it is, then you could get stranded at any time.
 
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