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Discussion Starter #1
Hello all,

I have a 2005 MDX with 173k on it; Literally just got it a few weeks ago (private sale for almost nothing... so not bitter) knowing about this issue.

Here's what I know: (Same for both hot and cold engine)

1, Reverse gear has no issues
2, Shift into D5, and it's there instantly - no waiting
3, Drive off, but does not shift at all

Stop car.

4, Shift into 1, pull away
5, Shift into 2, it changes to 2
6, Shift into D3 (or D4/D5), and it changes back down to 1

I've looked at the oil level stick, and personally I think it's over full - pictures attached of clean stick, and then immediately after checking levels.

Previous owner was told (by Acura dealer) that it needs a new tranny for $5k and nothing else will fix it. Hence she gave it to me for almost nothing.

Any ideas? Is it really in need of a new transmission and nothing else?

I've read that overfilling ATF can be as bad as low level ATF, but could it be the cause of this issue?

Thanks
 

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Dealers ALWAYS tell you that the "only fix" is a new transmission, so I'd say you should at least start out with the assumption that you might get lucky on this one. I once bought a very nice Volvo (V70 T5) for chump change because it "needed a tranny". What it really needed was a $30 part that took me about 30 minutes to replace. ;-)

Anyway, there are a host of things that can cause shifting problems - normally this starts with horribly dirty fluid, but yours looks pretty good. Either the PO had it flushed trying to fix it, or it's had regular fluid changes. I would certainly suggest getting the fluid to the correct level - get the car up to full operating temperature (probably a challenge given that you can't go over 30mph...) and then park it on level ground, and check the fluid within 60-90 seconds. It should be between the "dots".

Beyond that, there are a host of shift solenoids, sensors, and valves that can cause all kinds of mischief. It's a LOT easier to troubleshoot a transmission if you can get your hands on a laptop and HDS (Honda Diagnostic System) software and cabling. With it you can monitor the condition / position of every sensor and shift solenoid, as well as twiddling the shift solenoids manually (so you can hear if they're "switching" or not). The alternative of trying to troubleshoot by throwing parts at the tranny based on the symptoms can get expensive and time-consuming, but can also work out if you get lucky.

And finally, are there any flashing lights (like the D5 light)? That might be telling you something, too (and might not require an HDS to troubleshoot).
 

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Discussion Starter #3
hey habbyguy,

Thank you SO MUCH for throwing your thoughts into the ring - I really appreciate it.

Just drove it down the (long!) driveway, and can confirm no flashing lights; 1,2,D3-D5 and R are all steady green, P & N being steady red.

Just to reiterate, driving it "manually" from 1st to 2nd works fine, then from 2nd to D3 it reverts back as if it was shifted to 1

side note:, the "A/T Temp" light came on briefly (went out as soon as I came to a stop) - this is the first time i've noticed this. That said I've done about 4 miles in the car since I bought it a few months ago (havent touched it during the snow!!!)

I took a quick look on ebay for HDS, and they range from almost nothing to $2k so I guess I need to poke around more to find what I need; I have many laptops in the house, so that's no issue.

And finally at this point, the speedo/odometer aren't working - previous owner said they were working fine before Acura dealer got it. (so... back story - car wouldn't shift, so owner had it towed to acura, they had it 24 hours, gave her a $5k quote, she said no, they put it back together, and now speedo isn't working) - I'm willing to bet a dime that this is related to the dealer.

Thanks again
 

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Shouldn't be hard to find the speedo problem. IIRC, the speed sensor that feeds the speedo might also supply info to the transmission... you might just get a twofer if you fix the speedo! ;-)

The HDS I got runs on an XP machine (though I suspect it will also run on a newer machine running an emulation), so I just got an old laptop for "garage duty" (I have other similar dealer clone software, and it all seems to want to run on an XP machine, which is great because they're so cheap and plentiful). I think mine cost a little over $100 and has a big gray interface box with a few lights on it. I see others now that don't have that box, but don't have a clue how they work (or if they work). I know it was fairly fiddly to get my HDS installed and running (which is common with the clones) but it was really worth it - I can drive along looking at all the statuses I'd ever need to check on the transmission real-time. That's come in really handy with a buddy's Odyssey van (with a similar transmission, though one with a sordid reputation).

I would make sure the fluid level is spot-on, then take it from there. I predict you'll dodge needing a new transmission, since the problem seems to be in the logic end of things, not the "turning horsepower into motion end of things".
 

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Discussion Starter #5
Hey Habby & anyone else out there ^_^

At 10f its not great fixing-the-car-weather but I have been out there, and looked at the sensors - there's a few of them in the area; the speed sensors are between 50 and 70 bucks each (input speed & output speed)

Which is likely to control the speedo? input or output?

It makes some logical sense that I can access gears 1 & 2, but it wont shift to D3 because the computer thinks im travelling too slow. Furthermore if I go a mile in D4/D5 (for which it selects 1st) it goes into limp-home mode.

So which sensor shall I start at?

There are no right or wrong answers :)
 

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Looks like the output shaft speed sensor (aka countershaft speed sensor). It's the one that controls the speedo, and is tied into the gear position logic circuitry.

This should give you a good idea of where to look. Of course, with the recent service attempt, I'd suggest taking a long, hard look at the connection to the sensor before spending the $$$ to get a new one.

 

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Discussion Starter #7
Thanks... just ventured out into the tundra that is New England. There's a big plastic dirt cover over everything. Gonna need to dig out the ramps and get it up higher to remove that.

That said, there was a vent hole to look through, and enough gap to slide my flashlight in; I was also able to get my hand in there - they are 'awkward access' tight.

I read elsewhere that if I remove the sensors I can check they're working with a multimeter; This article was for a Ford, and the correct resistance was, IIRC, 500-700 ohms. Does anyone know the correct resistance range for these sensors; Hopefully I'll get under there in the next day or three.

Any & all ideas are welcome people - THANK YOU so much for reading!!!!
 

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Discussion Starter #8
ok... lovely day to get under an MDX!!

So.... I pulled the output speed sensor, and looks to me like it's been ripped apart..... pictures attached.

Now I have a choice - put a $50 part into the tranny and hope it doesn't get shredded.... or conclude that the tranny is, at minimum, ready to be rebuilt.

Your opinions please MDX'ers
 

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I can't even imagine how that happened... it's hard to believe that the rotating shaft below the sensor "grew" enough to munch the end off the countershaft speed sensor. And it's equally hard to believe that the sensor "grew" so it could reach the spinning bits. Wow.

I guess it would make sense to order a new sensor, and then carefully compare the "sunk length" of the new sensor to see if it's as long or longer than the original (which would pretty much guarantee a repeat of the damage to the sensor). I'm not sure, but would guess that it might also be possible to shim the new sensor to put it a bit higher (relative to the gear showing through the hole) than the old one. A rubber or carefully chosen aluminum washer/spacer might do the trick (I'm thinking that there won't be real pressure pushing out against the sensor, since it's clearly above the transmission fluid level).

The only other thing I can think of is that the magnet in the sensor attracted metallic bits that then got caught in between the sensor and the gear, and slowly took out chunks of the sensor. If that's the case, the magnet on your transmission drain plug should be REALLY ugly - covered in shiny metal bits.
 

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Discussion Starter #11
Hi Habbyguy,

At least 2 other mdxers have had this issue; Unfortunately neither reported back after replacing the sensor - I'm going to assume this is actually a good sign.

None of my local junkyards have any MDX's so it's gonna be a few days to get the new sensor (none of the local auto-part places have it in stock)

At the very least this should fix the speedo.... I wonder what the actual chances of getting a two-fer and fixing the shifting issues are...

I can only cross my fingers!!!

EDIT: Part ordered and will be here 8am tomorrow.........
 

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Discussion Starter #12
So.....

fitted the new OSS - took it for a test drive... speedo working... gear changes working.... smile on my head.... yes!

then DISASTER.... it chewed up that sensor and spat it out - less than 0.2 of a mile down the road.

I am so upset and frustrated right now... and $80 lighter.

I am thinking it was remarkably STUPID not to do a mega-flush.... and I'm guessing my next move would be to do said flush, hopefully find some chunks in it, then start all over again....

any thoughts??

:(
 

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Just did a quick check - rockauto.com has the sensors for just over $40.

2004 ACURA MDX 3.5L V6 Speed Sensor | RockAuto

Also, looking at the sensor, I don't see any reason why it wouldn't be possible to use a washer under the bolt (between the sensor and transmission housing) to move the sensor up just a hair. Obviously, move it too far and it won't work - but it's clear it's too close now, so (and this is important) once you measure the damaged and new sensors you can figure out how thick of a washer you'll need to allow the sensor to clear the gear that ate the last two. It looks like the O-ring that seals the sensor is low enough that moving it up a mm or two won't cause any leaks.

Why this is happening is another question altogether. If the shaft the gear runs on is out of true, or the bearing/bushing it lives in is damaged - then you'll probably run into other problems down the road. But if it was my car, I'd certainly install a ($40) sensor with a shim, and hope for the best.
 

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Discussion Starter #17
Hey... Habbyguy....

I was looking around online, and found that the alternative OE part numbers are: Alternate/OEM Part Number(s): 28810PR4003, 28820PCJ014, 28820PCJ017, SU7838

And if you put those into ebay one-by-one this is one of the finds:

NEW HONDA OEM 28820-PCJ-014 Transmission Speed Sensor/Vehicle Speed Sensor | eBay

$6 each.....

I'm gonna give it a couple hours for (a) me to think and (b) anyone here to chime in, then I think I'll order not one but 2 of those....
 

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Maybe I'm not seeing what you did - when I click on that link, I get a host of sensors... some appear to be the right one (and are around $40 and up), and some are obviously very different. I'd be careful - you're just not going to find the sensor you want for $6. If you did, I'd suggest buying a LOT of them and starting an Ebay reselling business! ;-)
 
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