hi, everyone first time poster.

I have a 1992 accord coupe with 4 cylinder and automatic transmission. It has 223k on it. The automatic transmission only has about 100k or so, I had it replaced a few years ago with a salvage yard unit. Now that I know a little more about my car I think the real problem back then was the TCU.

My current problem is that the car goes into limp mode (transmission in 2nd gear and will not shift) when it has sat overnight. If I unplug the TCU for a few minutes it will work flawlessly all day long with no problems after restarting during the day but the next morning it is back in limp mode.

The TCU was replaced with a new or reman unit when I had the transmission replaced a few years ago. The tag on it says OKI Telecom - Suwanee, Georgia. I looked inside it and it looks pristine, no burned resistors or leaking capacitors. The ECU also shows no evidence of burned resistors or bad capacitors. The ECU housing is dated 1992 so it may be original (I thought the shop replaced it also when they did the trans swap).

Some additional info: The check engine light does not come on but my D4 indicator on the instrument panel does not illuminate when the shifter is in D4. Park position does not illuminate either, the other positions illuminate on the instrument panel. The Cruise control will work occasionally but usually doesn't and the car occasionally does the up and down surging idle (coolant level is good and air bled from the system).

At this point I would just be guessing if I started replacing parts, hoping someone can give me some guidance on what to try next. thanks in advance.

 

The D4 light helps you see transmission codes.

On those accords, there is a little window on both the ECU and TCU. There is a light in there that will flash codes. I think the procedure is the same as the check engine light procedure, except you look in the window and count the flashes there. There is a link for checking engine codes in the common diy thread on top of the gen tech help forum.

I can't remember if you had to short the connector to check the codes on the actual computers. You can try counting codes with the connector shorted or not, and let us know what you find.

 

I have the TCU and ECU plugged in but loose from the mounting bracket, I looked over all sides, top & bottom of each and could not find a window. I took the covers off the units, jumped the connector and turned on the key, the Check engine, battery and Oil lights all came on and stayed on. No codes flashing at the D4 indicator and I could see nothing flashing or anything that looked like a light inside the TC or ECU.

Check engine light does not stay on without the jumper in place.

Edit: just checked the DIY section and found this: "On 86 to 90 accords, you just turn the key to the II position and count the flashes on the LED of the ECU or TCU to get the engine and transmission codes like in the above paragraph." Looks like from 91+ there is no LED light.

I have a wiring diagram, wonder if I could tap into the wire going out of the TCU to the instrument panel light and count readings on a multi-meter? Looks like it would be the wire labeled "D4 IND CONTROL"

2nd Edit: I just tapped into the "D4 IND CONTROL" wire with the CEL jumper wire in place and key on - all I got was a steady 12 volts with my multi-meter. That's puzzling because the D4 indicator light in the instrument panel does not come on.

 

What is the part number on the sticker for the ECU and TCU? For example, the Honda part number for a 92 AT DX ECU is 37820-PT3-A56.

 

ECU: 37820-PT6-A51
TCU: 28100-PXO-731-M13EX

Also, when I turn the key on with the jumper wire out the CEL comes on for 2 sec or so then goes out, the D4 light does not come on at all.

 

You have the proper ECU and TCU for your accord.

I always forget when honda stopped having that window on their ECU/TCU, but it was around 92/93.

As for the D4 light, you said that you have 12V for the light, but you never mentioned if you had ground. Let me see if I have any wiring information for your car.

 

I dont know everything for all the models of comps and rules, but I have a 92, and the d4 is what blinks for codes. Just cleaned my speed sensor to stop code 15 from tcu.

Does your d4 ever come on? Possible bulb burnt?

If u warm up the car drive a few or so blocks then shut it off does it work normall again?
Mine did that for a min, was shift and lock silenoids.. U can test those, I think u even might be able to with them on the tranny

 

I tested the solenoids, one seemed weak, I had a complete spare set that tested good so I changed them out to no effect.

 

Not sure how to check for ground unless I disassemble until I have access to the instrument panel. I had the multi-meter clipped to a major ground point on the passenger kick panel, it feeds to the instrument panel via a "junction B" on my Haynes wiring diagram.

I cleaned the ground at the thermostat housing, will see what that does. Next I am going to change out the coolant temp sensor. After that I guess I'll pull the instrument panel and check that D4 bulb. Sound like a reasonable process?

EDIT: Cleaning that thermostat housing ground appears to have fixed the cruise control....I'll see what happens in the morning with a cold start.

 

If you checked the 12V side of the D4 light with the electrical connector unplugged, then the other side (that would lead to the bulb) should have some resistance to ground. You don't want to see infinite resistance, just the resistance of the light bulb. EDIT: Depending on your meter, you may have to go through the different ranges of the resistance to determine if the circuit is open.