08 mazda 5 P0758 shift solenoid B questions

Hi All,

I'm having the same issues, CEL and AT, stuck in 3rd, hard shifts, every morning, but sometimes working fine by the afternoon. Unfortunately, I know NOTHING about cars, I only understood about 10% of this thread and I am terrified of this issue. I'm a young, broke girl who paid way too much for her '08 Mazda 3 with 100k miles. I've already put a new alternator into her this year, which wasn't my idea of 'cheap' and now the thought of a new transmission is keeping me up at night. I have NO IDEA what to do and I was hoping you guys might be able to offer some advice. Where do I even start? Go to the dealership as they might be able to know what is wrong right off the bat as mentioned above, and potentially save myself several attempts? Or go to a local shop and tell them to...? I honestly can't decipher what the issue here is, some people are saying electrical and others replace the solenoid... where do I start? Any help is so so much appreciated, I feel way in over my head!

Thank you so much.

The first thing you need to do is determine if the same trouble code is being triggered (P0758). Drive to your local auto parts store (AutoZone, Advance Auto Parts, O'Reilly Auto, etc.) for a free code check.

Then is can determined if this is an electrical issue and hopefully not necessitate the replacement of your transmission.
 
The first thing you need to do is determine if the same trouble code is being triggered (P0758). Drive to your local auto parts store (AutoZone, Advance Auto Parts, O'Reilly Auto, etc.) for a free code check.

Then is can determined if this is an electrical issue and hopefully not necessitate the replacement of your transmission.

Sorry I forgot to mention that, I took it to AutoZone last night and the code they gave me is: "P0758 Shift Solenoid B Electrical"

Googling that is how I found you guys :)

I just want to be sure of what to do/say before I call and make an appointment. That way I can feel better prepared for what they'll tell me I need, and what its going to cost me!

Thanks again for any help, I really appreciate it!
 
There shouldn't be much that you have to say besides telling them your symptoms - stuck in 3rd, hard shifts, etc. This type of repair does not require a dealer, just your local reputable mechanic. In one of my previous posts, I had mentioned the need for programming, but if your '08 Mazda3 is similar to the '08+ Mazda5, then that is not likely since the TCM is a separate module. Basically, any shop with a scanner should be able to give you a proper diagnosis. Talk to them about what you can expect, and if you don't feel comfortable with how they treat you, go elsewhere. Keep in mind that any repair shop will charge a diagnostic fee whether you already know the trouble code or not. It's just part of the procedure. The code is the clue, but there still must be time spent to determine the cause.
 
Solenoid is a device that use electricity to mechanically push / pull something. It is a "fancy word" for electrically controlled mechanical switch. In transmission valve body it controls whether fluid goes through one path or not.

Now when it is stuck in one position you can imagine it would engage the transmission wrong, which means wrong gear or burn up something (i.e. the clutch pack) somewhere.

The original poster found black grits in the fluid, that means it is already too late and has burnt something and is no longer electrical only.

Why the code, why the electrical only error? It may be the solenoid, may be the wiring or connector's plug, or may be the computer. Who knows which one it is unless you test all of them?

Unless the fluid has wrong electrical insulation spec or incompatible with the insulation material inside the tranny, I'd say this is manufacturing related instead of the fluid you put into the tranny.
 
valve Body diagram.

Hey all. Hope someone can help me here.
08 Mazda5, 110k, automatic. I got it at 97k, previous (1 owner) had all dealer service intervals done. Not positive on how often tranny fluid was changed, but it looks brownish.

Anyway, when the CEL and the AT light pop on, it shifts hard, esp in reverse. Clear the codes it shifts normal until the light comes on, which is quick. I haven't driven it very far since the lights have come on, hopefully a tranny fluid change will do the trick. Codes read P0758 code-shift solenoid B

Anyway, the biggest question I have right now, calling around for parts, none of the main FLAPS (NAPA, O'Reily, ect) even show the parts.
The local Mazda dealership showed 7 different shift solenoids, at varying <$100 prices, and wasn't sure which solenoid was 'B'.
I had it to the Aamco, and they think it may be just the shift solenoid sensor, but just speaking to the dealer the guy wasn't sure what sensor that would be.

Does anyone have any diagrams showing which solenoid would be regulated by shift sensor B, and where that sensor would even be?

Also, how can I tell exactly which transmission I have?

Thanks!
Hazen
 

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Hi all, this thread was quite useful because I just had this exact same problem.

Chessman, I joined this forum specifically to thank you. The symptoms you described matched mine exactly. I went through the diagnostic procedure in my shop manual and everything checked out ok, the diagnostic procedure then says "replace the TCM". Since the problem was intermittent I was convinced the cause was a bad electrical connection, the source of almost all intermittent problems. I could not believe the TCM could be the source of an intermittent problem. In many hours of trying, I could not find any conditions that would produce the suspected bad connection. Then I saw your post, so I ordered a new TCM and put it in. Fixed! Fortunately for me I am only out the $400 for the TCM and a bunch of hours in a cold garage. So thanks for sharing.
 
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