Environs

I've just recently purchased this car from a friend. Replaced the captive rotors (whew was that fun!) but now the car is having shifting issues with the auto transmission. When you start the car. The dash light shows park and d4 lighting up and the car will not shift beyond 2nd gear. Prior to this when driving the dash lights would switch from D4 TO D3 randomly but it would always shift through all the gears. I checked the fluid and it seems okay. Any suggestions where to start? At first I thought it was. Mechanical. But no idea think it's more an electronic or linkage issue. Thanks.

1991EX

My guess would be the TCU

Environs

sorry to be ignorant, but what is the TCU and is it hard to fix?

justinsbg

He's talking about the Transmission Control Unit, which is the computer that controls the transmission operation. It's a very common problem on 1990-1993 Accords. If you open up the unit you want to look for any burnt spots on the PC board around the capacitors(it's located behind the passenger's floor board and it's the bronz colored computer). It's usually one corner of the TCU that fails. It can be repaired, by me if you choose for about $80.00. I use better quality components to repair the TCU than what's installed. Check your codes as well. If you have shift solenoid codes you'll want to test them. Sometimes they fail which then causes the TCU to fail. If you don't fix the solenoids, the problem with the TCU will return. If you need any help diagnosing the solenoids I can help you with that.

Environs

justinbg, I did noticed the check engine light came on a few times when this started but then it went back off. I will try and pull the TCU and look at the board.

How do I check the codes on the shift solenoid? I am debating on getting a used TCU from the junk yard today to swap it out. Does it need to be an exact fit?

Environs

I took out both modules in the passenger foot kick and removed covers from each. Neither one looks like it has any scorch marks etc on the board and all of the connections seemed pretty solid. Other thoughts?

justinsbg

For the "un-seasoned" guy you need to look very closely at the PC board. There are numerous things you need to look for. Capacitors leaking, slightly dis-colored resistors, any signs of dis-coloration at all on the PC board. I don't recommend a junkyard TCU but if you have to do it then I guess you have to. The part number for the TCU will be under the words "at control unit" on the box ex. 28100-pxo-732. Try and find one from a vehicle similar in year, or part number. Like I said, it's an extremely common problem and a used TCU will probably be in bad shape or on it's way. If you want something that will last a long time get yours rebuilt. Re-check the board with a magnifying glass.

Environs

I just got back from a junkyard as I also got an oil pan (this one had hit something and wasn't leaking but the seal was bad so am replacing all of it). I did get a PXO-732 unit (the one in the car was a 722 unit); is there any difference? The junkyard unit came off a 93 Accord LX (mine is a 93 10th anniversary model). I'm going to throw it in and see what happens. I will inspect the original unit as well more thoroughly and reply back here.

Thanks for the help!

justinsbg

I'll have to check with one of my parts guys to see if there is a difference in part numbers. If you plug it up and everything works properly, I'd say go with it. I'm thinking there won't be much difference in those numbers. I'll get back with you about it a little later.

Environs

I just installed the 732 unit and everything seems to shift 100% a-okay now. Is there something else I should check (you mentioned solenoids) that could be causing the TCU unit to go bad. Or should I just run it as is? Amazing one little box like that causes so much trouble.

Environs

Interesting to note; After installing the 732 unit, it will start right up, drive, turn off, then when you go to immediately restart, it won't. I have to wait about 5 minutes then it's fine again.

So...I swapped back the 722 original unit and it was surprisingly fine for about a mile and then is started acting up again; would display P and D4 while driving, D4 would turn on and off intermittently while driving, and at one point after being stopped at a light, the D4 light flashed and I could feel the transmission slipping and not wanting to go into gear beyond 2nd (what the original problem was). Swapped back the 732 and seems to be okay. Draining tranny oil now, which looks as black as old motor oil.

What else should I do diagnostic on to see if it is something beyond the TCU?

Environs

Seems like the 'new' TCU unit has the transmission running slightly higher RPM. I noticed the RPM at about 25-2700 at 65mph whereas before it was right around 2100 or so.

justinsbg

Your post has me a bit confused. Are you saying that the TCU fixed your shifting troubles? Also, are you asking me for diagnostics on the shift solenoids? Definitely change the fluid. Older Honda transmissions are tougher than the newer, but the fluid needs to be changed at least every 30,000. I would change it now, drive it about 3,000 and change it again.

Environs

I did change the fluid last night. Old fluid was jet black so it was way overdue, not to mention a LOT of metal flake on the metal plug bolt. Almost looks like someone dipped the tip in Never-Seez. I'll take your recommendation and change it in a few thousand miles.

As near as I can tell, the TCU I got from the junkyard appears to have fixed the problem. Only thing I can tell any different is that it runs at a bit higher rpm's on the highway now.

Environs

Seems like teh new TCU is giving the car starting issues now. Sometimes it will start and then others it will not start = try and let sit for 5 minutes and try again. 50/50 it will start.

justinsbg

The TCU shouldn't cause the car to have starting problems. It doesn't have much to do with the engine cranking. You need to look elsewhere for cranking problems. What are the symptoms when the car won't crank? Is it temperature related, no spark, no fuel?

Environs

when it finally started tonight, it started right up, however a few hours later when I went to leave, it sounded like a grinding noise for a second and then actually started (whereas before it would do this and just not start). Could it be the starter? Odd that everything is starting to go at once. It did sit pretty much all winter in complete dis-repair though, so all the bugs are starting to come out I guess.

Environs

I'll check the spark plugs tomorrow and see what they look like. Sure they could use replaced.

josie625

I am experiencing the same problem with my 93 automatic accord 10 yr anniversity that has 176000 miles on it. I got my car checked out by a transmission shop and they could not detect what was wrong with my car. My car will sometimes show i'm in P and D4 at the same time. Also if driving on the highway once i hit 65-70, the car slows and becomes harder to drive. When i got the car look at the no codes came up but they said it could be the transmission solenoid. Is that the problem or could it be something eles?

bluebonnet

I've got one with the D4 light on. Won't down shift on its own, I have to shift down to first gear before it will engage. I then have second gear not shifted into, but I can then manually shift into 3rd gear

bluebonnet

We will pull the computer and examine it now.

totalaccord

If it's the TCU, it's an easy and CHEAP fix (even for a novice solderer like me). Here's the link that I used.


http://people.consolidated.net/etrid...ordtcufix.html

Hammer90

I just had the same problem with my 92 Accord EX with 1) showing both Park and D4 and 2) having acceleration problems.
I pulled the TCU. One transistor looked bad but tested ok. However - found someone who really knew capacitors and resistors at Radio Shack. The wires on several of the capacitors were burned out - but the capacitor itself did not look bad. The wires have to be looked at very closely. Anyway several capacitors & resistors were replaced and the car now runs like a champ. Cost me $20 total. New TCU from Honda is $630. Remanufactured boards run a couple hundred.
Also, be careful when you pull the board out of the TCU box - there are several small spot ties and screws holding it in.
I think there are several model for these boards so would use the same model. Mine was PX0-731. Honda has replaced that model with PX4-732 so that should be OK too. Would not bother with a TCU from a junkyard car unless very low mileage.

Numerous postings talk about the service check connector - never could find that little guy on my car - drove me nuts.

MAD_MIKE

Never found it?



If you had the carpet pulled back it should have been easy to trace it out from the harness. No loose or cut wires anywhere? I've usually found them tucked behind the right side kick panel just floating at the top.

honda.girl.1991

I am having the same problem, I hear a grinding knows, my P and D4 symbol are not on through. I just hear a grinding noise when driving. I know what is going on I have a 199656 miles in my 1991 Honda Accord. Is it te TCU?