TCU S light blinking no 4th Gear

[BreckAConner]

Good Afternoon,

Monday my CB9 decided it wanted to give me trouble. I went to leave work to go to another building and while starting the car up I noticed the S light was blinking and being in D4 I had slow acceleration. I've been manually been shifting between 2nd and 4th, but it doesn't matter if I'm in 4th I only get 4th gear only and no OD. Before this all happened I noticed on the highway at 75mph that the RPMs would flutter between 3000/3100 to 3500 on a straight road. Like it was switching between OD and 4th? Now when I drive on the highway with the S light blinking it's a steady 3500 RPMs. I'm not sure what to do, here are the things I have tried.

Reset TCU - Problem comes back after a few hours of driving

checked TCU - Board looks clean no burnt spots

checked/cleaned solenoids - click and looked clean to begin with

Here's the tcu codes I get: 1 2 7 8 14 ( I think maybe 4 or 5, can't remember)

Researching on other websites I have found to try and switch the ECU and TCU out, but I'm doubting that's my situation. I'm going to later try the ECU I have a extra PT6 for my Oddy build.

[oni_cb7]

The ECU has nothing to do with how the transmission is acting. It sounds like your issue is the TCU. I know that you said it doesn't look burnt, but I thought the same thing when I had this same issue. I took the TCU apart and looked at every tiny piece. It could be a burn, it could be a crack in the solder, or it could even be just a wet spot under a capacitor. Either way, it can be extremely hard to find the exact issue on the TCU (I spent 3-4 hours staring at mine to find the issue between multiple times looking at it). Eventually, I found two leaky capacitors and you could barely even tell there was an issue.

Do yourself a favor. Find someone with a working auto TCU (no issues driving the car). Swap this TCU into yours to see if the issue goes away. If so, then replace your TCU.

[BreckAConner]

The ECU has nothing to do with how the transmission is acting. It sounds like your issue is the TCU. I know that you said it doesn't look burnt, but I thought the same thing when I had this same issue. I took the TCU apart and looked at every tiny piece. It could be a burn, it could be a crack in the solder, or it could even be just a wet spot under a capacitor. Either way, it can be extremely hard to find the exact issue on the TCU (I spent 3-4 hours staring at mine to find the issue between multiple times looking at it). Eventually, I found two leaky capacitors and you could barely even tell there was an issue.

Do yourself a favor. Find someone with a working auto TCU (no issues driving the car). Swap this TCU into yours to see if the issue goes away. If so, then replace your TCU.

I hope I can find someone with the same accord, all my buddies have 5 speeds that I know that have CBs. I'm going to take a look in my garage and see if I can't find my old TCU unit from my other CB. I switched to a 5 speed with that car and I'm not sure where I put the TCU. I hope it's nothing major.

[BreckAConner]

Fixed it, was the TCU unit. I did try the ECU before you replied earlier so just in case any one asks the ECU didn't help anything obviously, and like oni said. Now when I went to the yard I pulled a 90/91 TCU and 92/93 TCU. My CB9 is a in between of a 91/92 since it was the first year it came out. I don't know why but my 91 has manual seat belts, has an airbag and came with a f22a6. All the other regular CBs of USDM coupe and sedan have auto seat belts, no air bag and have F22a1s or a4s (as I have seen). I don't know why they made the 91 CB9 this way, but it's just a little odd in my opinion.

My CB9 is a 91 and it has the sports mode button. When I put the 92 TCU in the CB9 it worked but the sports mode button didn't. The sports mode stayed on the whole time while driving. When I switched to the 90/91 TCU it fixed the sports mode button where it would function properly. The 92 TCU worked but I didn't want that sports mode light on my dash on constantly, I'm picky about those things. Hope this helps someone if they come across this thread.

[Fleetw00d]

Earlier this year I had two TCMs repaired by "mandigital" on ebay. You ship him your TCM, he repairs it and ships it back. Quick service (repaired and shipped within a day). Lifetime warranty. $75; more expensive than fixing it yourself (if you're handy with that sort of thing) or some used ones (no guarantee to work or last), but a heck of a lot cheaper than new ($600+) from Honda even if they were available. Might want to have the bad one repaired as a back up (or put it back in and keep the one in the car as a backup).