I'm trying to research and fix my 93 Accord. D4 light is always on, My D1 and D2 (and Reverse) gears always work. Every once in a while, after about ten miles driving (in 2nd gear), D4 light will turn off and if I shift to D4, tranny will work as intended. The big problem I am having is I don't get any codes. My check engine light has never come on. I have tried many times to short the plug under glove box, and I'm wondering if I'm using the wrong one. Anyone else had problems without the CEL or D4 light flashing a code? CEL light is not burnt - it comes on when I start car, then goes off. I'm hoping to attach pix of plug I used to get codes, and the other possible problem with tranny - the connector to a possibly shorted shift solenoid. But without codes, I'm stuck.

 

Since the Check Engine Light (CEL) comes on (for ~ 2 seconds) and goes off after you start the car means the ECU is probably good. As there is no CEL, this means there is probably no ECU trouble codes.

The TCU monitors transaxle operations and if a fault code is stored will turn on the D4 indicator light. TCU trouble codes are not the same as ECU trouble codes.

Since your D4 light remains on steady and does not blink when you jump the blue service connector (yes, that is the correct connector from your pic), it may mean a problem with the TCU. First try to reset the TCU by pulling the 7.5A back-up use from the under-hood fuse box for about 10 seconds. If there is no difference, then pull the TCU and open it up to visually inspect for burnt resistors or blown capacitors.

Honda Electronic Transmission Problem- Troubleshoot, Inspection, Repair, Replace.

The shift solenoid may also be the source of a problem too.

 

Thank you. I just figured I'd have to get some code(s) from either the CEL or the D4 light, as did so many of the other people who posted. Checking out the TCU is my next step, but I was really hoping to get a code first, to verify that indeed it was the solenoid. I should mention that at one time I disconnected the battery for a day, and the D4 light came on as soon as I turned the key.
I'll post an image of the TCU whether there's obvious damage or not, and take it from there.
This is tricky stuff....I appreciate your help.

 

Removed TCU today, seemed OK compared to other posts, but when I magnified pix, seems like possible leakage on capacitators 28 & 33. Hopefully someone out there can confirm damage. If so, how the heck do I replace these? Seems like I'd need magnifiers and jeweler's tools...
Also wondering if this might have caused the short on the shift solenoid connector or is that a separate problem??!!

 

Does look like damage. You would desolder the damaged components with something like a solder wick (desoldering braid) and an soldering iron. Many people do use magnifying lamps during solder work; but, it can be done without it. I like to use solder tips with a fine tip. Some guys at electronic part shops or electronic repair shops will sometimes only charge you a little to replace, as it is only a few minutes work if you bring the board to them.

The solenoid and/or solenoid connector may be a separate problem.

 

I hear people saying they had good results just by "cleaning the solenoids" What does that mean? Am I supposed to spray a solvent through the openings, or somehow disassemble the actual solenoid part? Otherwise both assemblies looked good when I removed them - filters clean and fluid bright red.

 

"Cleaning" the trans solenoids is really making sure the "cone" is seating off to the housing. They don't come apart....or should I say they do but don't go back together ...for cleaning. In the link below you will see them apart but DO NOT do this. The pic is for "example" and to show the internal workings.

Honda Electronic Transmission Problem- Troubleshoot, Inspection, Repair, Replace.

 

I gotta say that one image in the link is the one I had seen earlier that got me to wondering if I had to disassemble them. Thanks for setting me straight there.
I'm sorta doing what I can while I wait for the capacitors to be shipped to me. I checked the resistance - 15.9 to 15.6 on all. Plus, they all clicked when I applied current.
Still, I read somewhere else to pour carburetor cleaner in the openings while applying current to activate the solenoids and clean the insides...should I do this while they're out?

 

If they are out already.....you won't hurt anything.

Just me here but I like brake cleaner for these types of things. True "carb" cleaner is designed to leave a "film" behind where brake cleaner is not....there is a chemical engineer on here that can correct me or chime in......if we want to get down to the difference in the chemical make up between the two.........

EDIT: I realize the amount of residue left by carb cleaner vs. brake cleaner is so small it really doesn't matter.....just making a point.....sorry.

 

Finally got TCU back from repair shop, replaced three capacitors. Installed it and got the same results, except when I got back from test drive the D4 light would turn on just briefly, then go off, for the next three times I turned key from lock to II position. Has something to do with ATF or tranny warming up enough to allow things to work as should, maybe? After an hour, D4 light was on constantly again.
What's killing me is I'm still not getting CEL or D4 codes so I can't diagnose. I know CEL works, cause it gave me the correct code when I failed to reconnect IAC sensor. Starting to think that something else is messed up with TCU if it can't give me codes...
The only other thing I'm thinking might be bad is that the shift solenoids don't click anywhere as loud as lockups do. I have a chance to buy both sets used for $100 locally and might do that, unless someone has any suggestions or confirms solenoids should all sound the same.
Waiting patiently for any help...currently unemployed, so I got plenty of time