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Bad TCM? [Mazda3] (www.reddit.com)

submitted 2 months ago* (last edited 2 months ago) by [email protected] to c/[email protected]

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I let the smoke out of the automatic transmission of my 2007 Mazda 3 and it's at Aamco now. What apparently happened is I got a tear in the boot of the passenger side CV axle, which let out the transmission fluid. The Aamco guy said my transmission is ruined, which seems fairly obvious to me, so I found a remanufactured one online for a better price than what Aamco would offer. They agreed to install it anyway and even with their labor estimate I'm saving a good amount of money.

The trouble is that now that they've started work and have removed the old transmission, they're telling me that the old TCM, speed sensors, fluid pressure transducer, and neutral safety switch have also gone bad and cannot be reused. Based on a previous experience, I believe they are correct about the neutral safety switch, but I am doubting the diagnosis on the TCM. I asked how they made this determination with the TCM and the reply via SMS was "WE DETERMINED IT WAS BAD WHEN SCANED WITH THE COMPUTER THERE WAS NO COMMUNICATION WITH THE TCM". After I let the smoke out and the AT light came on, I limped home in fourth gear and then scanned for codes. I came up with P0733 (Transmission Gear #3 incorrect ratio) and P0894 (Transmission Component Slipping). If the TCM was not communicating, wouldn't I have gotten a U0101 code?

I'm not trying to be a cheapskate, but a replacement TCM isn't cheap and I don't want to spend more than necessary.

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[–] [email protected] 1 points 2 months ago* (last edited 2 months ago) (1 children)

CV boots don't hold fluid in the transmission. That's held in by a seal in the transmission housing. That they told you this is all you need to know about AAMCO.

Get your car out of that ripoff known as AAMCO, and into a small local shop - ~~they'll source a good used transmission and replace it,~~ likely for half or less of what AAMCO is going to charge you. Edit because I missed you already found one.

I replaced a Honda transmission recently (auto), it was $800 via ebay (came from an outfit that sells large components like this). It arrived perfectly clean, wrapped and pallete. Then replaced it in an afternoon.

If the TCM was bad, it would've died before the trans quit... So you would've had lights, and it wouldn't have shifted. The transmission dying isn't going to kill a TCM. Losing fluid means the clutches overheat and glaze, which really reduces their coefficient of friction (they slip). Nothing about that would affect a TCM which is a very robust, purpose-built, control module (some would say computer, I'd say more like a CNC). Sounds more like they hooked it up wrong, or the wrong transmission was sent (sometimes there are similar transmission thatcan look nearly identical, but have different configurations of controls).

AAMCO is a combination of incompetence and snake oil salesmen.

[–] [email protected] 1 points 2 months ago

I am also suspicious of these sorts of chains, but my usual mechanic couldn't take the job and Aamco was the only local transmission shop who would pick up the phone, so here I am. ¯_(ツ)_/¯ Anyway, I took the allegedly bad TCM from them and I'm going to send it to Upfix for testing and repair. If Upfix says it's actually fine, they'll just charge me a bench test fee and then I'll have to have a confrontation with the people at Aamco.