pgrandstaff

92 Acccord EX, 2 door
206k miles

A few months back my car started down-shifting harshly when it shouldn't, for instance at cruising speed on a highway. The ATF fluid was low. I topped it off and no problems for 30+ days.

Then, the down-shifting issue returned out of the blue. This time, after a few instances of unwanted down-shifting the D4 light would come on solid. I was able to manually shift between 2nd and 3rd (I believe.) Cutting power to the computer and restoring would resolve the issue for 40 or so miles.

After a bit of this (and me doing lots of reading on this forum and at Techauto) it stopped giving me any troubles. During this time, I pulled the TCU and had a look at the board. It looked perfect. I saw no sign of any burned out components.

Everything ran perfectly for 2.5 or 3 weeks.

Today, I went down to the store. It started raining while I was inside. On the drive home, the down-shift hit me again, once I got up to about 63mph. It seemed worse than before.

I'm not sure if the rain is a clue or a red herring.

This time, the D4 light did not stay on. The car does seem to be stuck in 2nd gear though, no matter where I put the shifter. Cycling the power to it resolves the issue, but it returns in 1 to 4 miles.

I took it to a local Honda repair shop and had them change the atf fluid. The technician there was 100% my troubles are due to a bad computer, even though the board looks fine.

What do you think? Could it be the speed sensor?

It has not given any error codes, but I did not check while the D4 light was stuck on.

They quoted me $300 to refurb the tcu with a 3 day turnaround.

I see I can buy them for less than that online, and am comfortable with the work required to install it.

But, is there an advantage to having a shop do it? Any advice for shopping for a new one?

UPDATE: Checked error codes again, and the D4 light blinked a 15. Should I be looking at the NM Speed Sensor after all?

tamadrummer1120

From Code 15 you are getting an error with the mainshaft speed sensor. The the Vehicle speed sensor though. Do not get them confused. You would have a CEL if you have a VSS issue. You would need to check to make sure that the 2 pin connector going into the MSS has the proper voltage, continuity, and the correct resistance. Which can ultimately lead to a replacement in a new TCU.

But something else.....you transmission does not just 'loose' fluid. You may want to look into that. The fact that it is low and you have to top it off. That seems like an issue that need to be addressed as well.

pgrandstaff

Thanks for the answer! I'll check out the mainshaft speed sensor first thing in the morning.... looks like it should be within 400-600 Ohms. Not sure about voltages.

Yes, the low fluid scared me a bit. I've been watching it closely since and have observed no further loss over 2 or 3 months. I went quite a while where I simply didn't give the car the regular maintenance it needs. (Stupid, I know.) So, I'm hoping the loss of fluid was due more to the fact that it was ignored for too long than leakage or worse.

tamadrummer1120

well like i said, it shouldnt just 'leak'. check under the car to make sure there is no leaks visible. low trans fluid can have a very negative effect on auto trans' (obviously haha), but especially with these older, higher mileage ones.

Frank Allen

i have bought several tcu s at junk yards for 50 to 100 dollars, be sure to get the correct number. they all look alike but are not
Frank allen

pgrandstaff

Thanks, Frank. I'll be sure to match the numbers on the old unit.

Now, on the mainshaft speed sensor... I've located it, and will be checking resistance later today. What I'm unsure of is how to actually access it. Does anyone know the proper way to get at it?

It looks like I either need to remove the battery and battery stand or come at it from underneath.

I have not seen any leaks under the car, and the fluid level hasn't changed since the one time I topped it off. I'll continue to monitor it though.

pgrandstaff

Resistance reading was 494 ohms at 12 C (55 F), which seems to be in normal range to me. Going to try to clean the sensor itself if I can get it detached tomorrow.

holmesnmanny

I had a leak in the radiator connection a month ago or so. Also, there is a nut on that connection that can come loose. If it's leaking there, try tightening it up with a crescent wrench from under...You'll have to just drop the splash guard.

pgrandstaff

Well, I got under the car and discovered my cheap ratchet just won't handle the bolts on the splash guard. I poked around as much as I could looking for ATF leaks, but didn't find any sign of red fluid. There's definitely an oil leak, but no hint of red.

Going to take it into a shop and will post whatever I find out.

Thanks for the help.

pgrandstaff

Got the verdict today: Internal transmission trouble, requiring a rebuild.

They tested the computer and said it was in great shape, so glad I didn't replace that.