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Discussion Starter #1
2010 Mazda 3 hatchback won’t start, forgets (electronically) it’s in park when sitting overnight.

Please help, I’m at a loss,... Ive tried everything I
can think of. .... consisting of: 2+ weeks at
dealership, over 1000$ in parts/labor and over
30hrs of my own time trying to fix it. Nothing fixes
problem.

My wife has a 2010 Mazda 3 hatchback, automatic, 2.5l. The car basically “forgets” it’s in park when sitting overnight (or long periods of more than 3-4hrs) and therefore wont start. You have to either wiggle the shifter (25% of time) without switching gears or go from park to neutral and back to park (75% of time) .... then it remembers, and it starts. By “forget” I mean Electronically doesn’t recognize and doesn’t light up the green “P” indicator even though mechanically it is in park. So it doesn’t think it’s in park, so it won’t let you start it.

Once it runs, it runs fine. No issues. Shifts through gears perfect. No codes on any reader. Goes into park fine (lights up). Can be re-started if it’s less than an hour or two. Like no issue at all. Then leave it overnight and problem back next morning like clockwork.

I’ve tried all usual things to fix it, and Every time it works for either a day or two and it returns. Or not at all. So far I’ve replaced/adjusted:

Neutral safety switch (3x actually, incase I got bad ones and both aftermarket brands one from
autozone, one from oriely’s, and one for action auto).

Dealer-replaced the lever, nut and washer coming
from transmission. Per some service announcement on an older model. It was corroded at time. That lost me car for two weeks while they ordered it. Issue came back 4 days later.

Brake-Pedal sensor. No change.

New battery. (It was 4.5 years old and one day it
was dead in morning, no obvious sign what drained it. Just opted to buy brand new one due to age, been fine for a month since. No issues).

Adjusted the shift cable Multiple times. Adjusted
the neutral safety switches multiple times. Made sure all lined up. Cleaned connection clips.

I just finished replacing the entire shift cable. And
the bracket that holds it to the transmission (in case bracket was bent or internal corrosion or kink in cable). Ordered both OEM from Mazda dealership but put them in myself. Repair last half day, next morning issue returned like clockwork.

Cleaned little black switch inside shifter housing.
(Tiny metal flap that has two small wires. Can’t
reach it since 8mm bolts that hold top panel spin but don’t come out. But cleaned dirt and discolored grease off. Makes a faint clicking sound when car goes into final park. Not sure what this “does” but I’m desperate, so I cleaned it).

This problem has been going on for 5+ months. So annoying. And I’m literally out of ideas. Anyone have any possible causes? I can’t find anything else on internet.

P.s. I did see one for a manual transmission said it was a corroded wire into starter, but that doesn’t seem to be issue on wife’s car. Wire seems fine and car does start no problem once it electronically knows it’s in park and can.

Had one suggestion to replace wire leads inside clip to neutral safety switch, possible corrosion there. But haven’t tried it yet and no obvious signs of corrosion in clip itself.
 

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So what exactly happens when you turn the key? Is there a click? Does anything on the dash light up? Could it be the AT control module (the one located under the battery, at least on my 2004) going bad if you think it's electronics-related? I believe it's the computer that controls the ATX but you'd have to replace the entire module in order to verify and they're typically not cheap. Did you inspect the switch/fuse/relay box in the engine compartment or perhaps yours is in a different location. Apologies again, I have a 2004 so I'm used to where everything is on that generation.
 

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Discussion Starter #5
It is a push button start, so no turning of key.

And everything lights up except the parking “P”, (radio works, lights etc.) but it won’t start because it doesn’t think it’s in park. So it doesn’t disengage the safety feature. No click, since it won’t even send power to starter (which is fine btw) to try.

Remind it it’s in park with a jiggle or a quick switch from park-to-drive-back-To-park and try again and the “P” lights up And it starts up nice and smooth first try. Then it runs smoothly all day, easy gear shifts, starts and restarts first shot multiple times and no issues at all. Leave it sitting overnight and next morning issue returns like clockwork and have to remind it again.

And yes, to answer where the other post is going. Brand new neutral safety switch (3rd one in six months bc that’s the obvious choice so I keep trying in vain hoping the prior ones were just bad lol) is adjusted properly, as is the brand new shift cable (went thread by thread with two people ensuring exact adjustment). No issue at all with where gear is Vs what is showing. And the lever on the transmission pin is brand new also bc I already took it to dealership to fix this issue and they kept it for two weeks and changed that out for me. Ensuring me it would fix the problem. It obv didnt.

All parts from the tranny pin to the inside shifter are brand new, shiney and properly adjusted.

I’ve got this question posted on 5 repair forums and no one seems to have experienced anything like this before.

So far closest “ideas” I can try next is a bad ground lead somewhere near NSS. Perhaps inside the connector pin harness (like water got inside), a bad -#7 ground on the tranny case itself for the TCM, or a bad primary ground under the battery box (unlikely, since I had that off to install the cable). But it’s been raining for two days here so can’t (I won’t) open electronics up at all until it’s nice and sunny and dry out.
 

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Discussion Starter #6
Any other possible thoughts?

Others have mentioned possibly a bad TCM or a Bad computer; but at over $800/ea it’s not something I buy and hope for the best. Since car works perfectly once started, anything over about $300 doesn’t make sense on the cost to benefit ratio. At that point I just politely ask the wife to deal with it forever, buy her something nice to distract her and duck when I tell her 🙂 lol
 

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Strange problems

Reminds me of a car problem story somebody once told me. Old Dodge truck refused to start every morning until about 10 am. Dealer baffled as well as several independent mechs. Finally somebody decided to look a little closer at the distributor cap which appeared to be brand new. Found some mold growing on contacts. Scraped off and truck started. Changed out the cap for one that sealed a little better. Problem solved.
My version was my 94 F-150 that kept dumping me on the road and refusing to start. Once I got it to a shop if would behave perfectly. Got tired of dealer throwing parts at it. Finally got it to act up at an independent mech's shop. By then, whatever it was had ruined the computer. They kept it for several days tracing wiring in between other jobs. Finally found crimped and almost broken wire on the radio noise suppression capacitor that intermittently ground out on the engine block. I had noticed this wire before, knew what the part was, and just didn't think it important. Point is, problem is likely staring you in the face. You will find it and probably kick yourself for overlooking it. Hope it happens soon. Good luck.
 

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2010 Mazda 3 hatchback won’t start, forgets (electronically) it’s in park when sitting overnight.

Please help, I’m at a loss,... Ive tried everything I
can think of. .... consisting of: 2+ weeks at
dealership, over 1000$ in parts/labor and over
30hrs of my own time trying to fix it. Nothing fixes
problem.

My wife has a 2010 Mazda 3 hatchback, automatic, 2.5l. The car basically “forgets” it’s in park when sitting overnight (or long periods of more than 3-4hrs) and therefore wont start. You have to either wiggle the shifter (25% of time) without switching gears or go from park to neutral and back to park (75% of time) .... then it remembers, and it starts. By “forget” I mean Electronically doesn’t recognize and doesn’t light up the green “P” indicator even though mechanically it is in park. So it doesn’t think it’s in park, so it won’t let you start it.

Once it runs, it runs fine. No issues. Shifts through gears perfect. No codes on any reader. Goes into park fine (lights up). Can be re-started if it’s less than an hour or two. Like no issue at all. Then leave it overnight and problem back next morning like clockwork.

I’ve tried all usual things to fix it, and Every time it works for either a day or two and it returns. Or not at all. So far I’ve replaced/adjusted:

Neutral safety switch (3x actually, incase I got bad ones and both aftermarket brands one from
autozone, one from oriely’s, and one for action auto).

Dealer-replaced the lever, nut and washer coming
from transmission. Per some service announcement on an older model. It was corroded at time. That lost me car for two weeks while they ordered it. Issue came back 4 days later.

Brake-Pedal sensor. No change.

New battery. (It was 4.5 years old and one day it
was dead in morning, no obvious sign what drained it. Just opted to buy brand new one due to age, been fine for a month since. No issues).

Adjusted the shift cable Multiple times. Adjusted
the neutral safety switches multiple times. Made sure all lined up. Cleaned connection clips.

I just finished replacing the entire shift cable. And
the bracket that holds it to the transmission (in case bracket was bent or internal corrosion or kink in cable). Ordered both OEM from Mazda dealership but put them in myself. Repair last half day, next morning issue returned like clockwork.

Cleaned little black switch inside shifter housing.
(Tiny metal flap that has two small wires. Can’t
reach it since 8mm bolts that hold top panel spin but don’t come out. But cleaned dirt and discolored grease off. Makes a faint clicking sound when car goes into final park. Not sure what this “does” but I’m desperate, so I cleaned it).

This problem has been going on for 5+ months. So annoying. And I’m literally out of ideas. Anyone have any possible causes? I can’t find anything else on internet.

P.s. I did see one for a manual transmission said it was a corroded wire into starter, but that doesn’t seem to be issue on wife’s car. Wire seems fine and car does start no problem once it electronically knows it’s in park and can.

Had one suggestion to replace wire leads inside clip to neutral safety switch, possible corrosion there. But haven’t tried it yet and no obvious signs of corrosion in clip itself.
There's been a lot of parts swapping, some of which doesn't make sense. Based on your statement of moving the shifter, I'd say it has something to do with a switch, wire, or connector. It appears some of the items you adjusted are the ones I would have attacked as well. I'm going to argue against the TCM unless you can find one from a scrapyard to use as a test. There's something in the path of cycling the shift lever that's causing whatever is out of whack to work. The transmission for my car was rebuilt a couple of years ago, and there are times when I shift to part the 'P' is not illuminated. I attribute that to a linkage out of adjustment; however, I have never experienced the lack of starting issue which has plagued your car.

Looks like you have some serious troubleshooting that's going to irk you to no end. Keep at it as I am one of those who would love to know the resolution.
 

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do you have a wiring diagram and multimeter
measure the neutral/park input to the tcm before and after the jiggle
 
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