1990 accord LX tranny problems.

Well I'm working on my sister's car she has taken it to AAmaco twice and spent 700 bucks and nothing was fixed. So now I got to take a look at it. We start the car up and start driving around everything shifts great. However once the car is warm then the tranny will stay stuck in 4th or 3rd. It won't downshift so when you start to take off the car is dragging and barely able to move. I can however shift through the gears manually. If I drop the lever to 1st then the gears change and I can take off. AAmaco said after the Diag that it was the shift control solenoid and replaced it and called us back stating the car was done. So I go grab the car start driving and as soon as it reached operating temprature the problems started happening again so naturally i took the car back and wondered why the hell they don't test drive the car after the work was done to it adn was assured it was test driven "Extensivly." Last night I go pick the car up again because it was a "loose connection" on the new control solenoid and again operating temp the car wouldn't shift. I call them up and was told they need to do a soft tear down on the tranny and we need to pay another hefty sum that the car just isn't worth that much.

Any Ideas on what I should look at or look for in order to get this working? I know manual transmissions like no other the automatics confuse me a little.
Thanks in advance for the help.
Nate

I am sorry to hear about this!
I am not big help in transmissions but I have just one word for you:

DO NOT GO TO AAMCO any more. I paid them about Three thousand dollars in one year!!! for two trannsmissions with no luck.

I hope somebody with better knowledge in transmissions will respond...


Good luck,

Sam

It's hard for me to offer anything useful at a distance...but it does sound a little familiar...

A friend's '89 Camry was doing something nearly identical.

First, I don't know how far your knowlege of these trannies goes, so bear with me.

You have the valve body, it uses a hydraulic circuit to open valves that make shifts at certain pressures. The pressures are governed by engine speed, the faster the engine runs, the faster the pump in the tranny turns.

So at it's most basic, the tranny will shift based on road speed, when the engine's RPM climbs to the point the pressure is at the threshold for a shift, a valve in the valve body opens and allows fluid into a new circuit, that makes it shift into and hold the next gear up, and so on...

To allow it to be able to hold a lower gear longer, to help it under load or hard acceleration, you need a way to sense engine load and delay the upshift when needed. We used to do that by vacuum modulator, manifold vacuum is directly related to engine load, under load vacuum is very low, so the modulator would override the valve body's operation until a higher vacuum level returned, then it would allow the valve body to make the shift happen.

Then in the 80's a lot of them went to detent cables, it was the cable that ran from the throttle down to the tranny. It used cable position to override valve body operation in the same sort of way...the harder the gas was pressed, the more pressure was needed to overcome that override, and upshift was delayed until higher rpm or the throttle was released somewhat....

Then we went to electonic control. This mates the throttle position sensor to the tranny control computer along with vehicle speed info from the VSS and other inputs to decide when the proper time to shift is.

There is probably two shift solenoids on that tranny....they work like binary code to provide the correct valving for each gear (1-4)...so for instance (this is not correct, just for reference, your manual will show the actual pattern for yours) they might work like this:

Sol#1 Sol#2 GEAR

OFF ...ON ...FIRST
OFF ...OFF.. SECOND
ON ....ON... THIRD
ON ...OFF.. FOURTH (OD)

So the TCU applies the proper combination to the solenoids to hold the gear it wants it to be in...if a solenoid doesn't work, or gets stuck applied (depending whether it's supposed to be on or off when the problem occurs), it will cause a gear to not engage, and/or get stuck in another gear.

So if say in my example #1 gets stuck applied when it warms up, then when it should be in first (OFF-ON), it will actually be holding in third (ON-ON, because #1 is stuck on) and you will have what you have....and a command for second (OFF-OFF) would actually be a command for fourth (ON-OFF)...this is just an example, but depending on the actual logic pattern the solenoids use, a solenoid failing to operate (stuck OFF) would produce the same kind of problem.

These kind of problems can get tricky...I would hope they actually verified that there was a problem with the solenoid they replaced...if so, you may be dealing with something hard to find, like a wiring sag that lays down or shorts out when the engine warms up, and the solenoid was not working right because of that and not the part itself or another issue with fluid pressure inside the valve body, not even related to the electronic control.

You could try unplugging the TCU and see what happens...if it seems to improve without it's influence, then it can be assumed the problem is in that part of the system, so a solenoid, wiring, or TCU could be suspect. You'd need to umplug it after it has sat and cooled off, because if there is a problem with a solenoid sticking after warm-up, it will remain stuck and still cause the problem even after unpugging the TCU, at least until it cools off and releases.

So when you drop it down to low and take off, do you then have to upshift manually through each gear, or do you just throw it back up to D4 once it downshifts, and it upshifts up OK on it's own? The difference is critical, I need to know which it does.

So when you drop it down to low and take off, do you then have to upshift manually through each gear, or do you just throw it back up to D4 once it downshifts, and it upshifts up OK on it's own? The difference is critical, I need to know which it does.
I never tried that... I'll try it next time I get a chance between school and work. After reading the symptoms (I forgot to mention the s light flashes) It seems more of a tcu/tcm problem. Anyone know if it is just the capacitors that go bad? If so I can replace them and be on my merry way (I've had to do that to at least three of my cars now is replace the capacitors in the ecu) I'll test it out and let you know what I find about the up shifting. I believe ijust put it to 4th and let it up shift on its own but I didn't pay enough attention to recollect.

I'm inclined to agree...it sounds like there's a problem with the electronic control end....usually if a valve body blows off pressure or sticks, or you have a weak pump or something that causes low fluid pressure once the engine warms up, you wouldn't have any manual control and it wouldn't upshift itself....

I don't know anything specific about the Honda TCU...the one in my friend's Camry was not serviceable...after I unplugged it and it to test a theory and the lower gears returned, he wanted me to just leave it that way....so I didn't get the chance to actually diagnose the root cause...

did you read the sticky post at the top of this forum about the S light flashing?

Yeah I saw it in the sticky. I went to pull codes and clicked the sticky to make sure the code was what i was thinking of then saw the flashing "S" after I posted this thread :banghead: Now I'm just trying to find out if I have to match any numbers or anything on the TCU/TCM and the range of years that would work. 90-93 sound right?

Yeah I saw it in the sticky. I went to pull codes and clicked the sticky to make sure the code was what i was thinking of then saw the flashing "S" after I posted this thread :banghead: Now I'm just trying to find out if I have to match any numbers or anything on the TCU/TCM and the range of years that would work. 90-93 sound right?


Hey! Jackpot!

I found this while trying to look up the TCU# for you...

Sounds like exactly what's happening to you, doesn't it?

Gives me more confidence it probably is the TCU...they said it is serviceable, so if you fixed that other one, you might could fix this one too...


1990-94 Honda Accord/Civic auto transmission controller ECM TCU removal directions:
The engine and transmission computers for the Hondas are usually located under the carpet of the passenger side floor/foot rest area. Remove the carpet, which may require loosening the door jam or trim areas of passenger kick panel. Once the carpet is pulled back you should see a large (and you'll find out soon, quite heavy) "bash" or protection plate. This can be removed by extracting the fastening screws to the plate and moving the plate to the side. There are two or three plugs in each unit. Depress the center of the tab and pull away from the unit. The transmission computer is the one with the prefix part number "28100" and the engine controller has a prefix of "37820". As we stated, the trans controller is much more prone for failure. Be sure to check your distributor and ignition components before investing in an engine controller. Most trans computers and repairable and you will likely be in "limp mode" or "fail safe" mode which is 3rd gear and rev only and the "D" or "D4" light will flash or stay lit. Often the Sped sensors or shift solenoids are adversely affected and must also be replaced. Be sure to have them tested before reinstalling reman trans computer.

Hey! Jackpot!

I found this while trying to look up the TCU# for you...

Sounds like exactly what's happening to you, doesn't it?

Gives me more confidence it probably is the TCU...they said it is serviceable, so if you fixed that other one, you might could fix this one too...


1990-94 Honda Accord/Civic auto transmission controller ECM TCU removal directions:
The engine and transmission computers for the Hondas are usually located under the carpet of the passenger side floor/foot rest area. Remove the carpet, which may require loosening the door jam or trim areas of passenger kick panel. Once the carpet is pulled back you should see a large (and you'll find out soon, quite heavy) "bash" or protection plate. This can be removed by extracting the fastening screws to the plate and moving the plate to the side. There are two or three plugs in each unit. Depress the center of the tab and pull away from the unit. The transmission computer is the one with the prefix part number "28100" and the engine controller has a prefix of "37820". As we stated, the trans controller is much more prone for failure. Be sure to check your distributor and ignition components before investing in an engine controller. Most trans computers and repairable and you will likely be in "limp mode" or "fail safe" mode which is 3rd gear and rev only and the "D" or "D4" light will flash or stay lit. Often the Sped sensors or shift solenoids are adversely affected and must also be replaced. Be sure to have them tested before reinstalling reman trans computer.
I like the repairable sound to that.. (read cheap) But I need a little more details and I have problems searching the intranet for some reason. I know Capacitors are known to go bad on these old computers but I'm wondering if there is anything else that would need to be replaced.