'92 accord - D4 light stays on - no TCU code
 

i started this adventure in another thread which can be found here

https://www.hondaaccordforum.com/for...14/#post278371

but i checked the error codes and have more info and questions now so i thought a new thread was in order. here's the story from the start.

my friend has a 92 automatic accord EX. approx 10 months ago she noticed it bogging down intermittently--sometimes several times a week, sometimes it would go several weeks without the problem. she said the check engine light would come on when this occurred but would not come back on when the car was re-started.

approx 4 months ago, the D4 light started staying on and once started in P, the trans could not be shifted out of P. if started in neutral, the trans can be shifted to other gears but the trans will not shift on its own and must be manually shifted through the gears.

i googled the hell out of the D4 issue but not the bogging issue because i didn't hear about the bogging until today. what i found online suggested the gear selector switch at the base of the shifter had failed so i replaced that. it did not fix the problem. i searched more and found people talking about the faulty TCU:

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

so i pulled the TCU and took a look but as i posted in my previous thread, there are no super obvious failures on the TCU. one of the diodes has a small brown dot on it that looks like it *might* be burnt but nothing like any of the pictures i've seen which show blackened crap all over the board.

today i found the blue error code plug behind the passenger kick panel and shorted it with a wire. the D4 light did not flash but the check engine light flashed the code 43, aka fuel supply system. this seems in line with the intermittent bogging down that my friend reported prior to the trans problem, which i suspect to be a dying fuel pump.

here are my questions:

1) is the same blue plug used to retrieve codes for both the engine and the transmission? if not, where is the trans code plug on a '92?

2) i have read that a faulty TCU can give the trans error codes 1, 2, 7, 8, 9, 15 or none. any idea what the chances are of receiving no code for a faulty TCU?

3) has anyone found any connection between the engine error code 43 and this shifting problem? i imagine that these are two separate problems occurring simultaneously but want to rule out the possibility that they could be linked.

4) any advice on anything else the fuel supply code could be for besides a fuel pump? i replaced the fuel filter on the car approx 15 months ago so i don't think it could have become clogged just a few months after that.

thanks very much for your help, guys.

1) yes
2) a good guess is a faulty TCU code give all or no codes, its faulty
3)
4) fuel supply could easily be low fuel pressure - proper method is to tap into the fuel rail with a gauge and get a reading.


Edit** a failing fuel pump could and would def cause bogging issues.

Also I posted a WTB cheap 4th gen TCU for you on another board. I have seen them going for $20 shipped there.

i posted this on the other thread but wanted to post it here as well because i hate repair threads that never conclude. much more helpful to the community to post findings.

so we got this fixed and it turned out that it was in fact the burnt diode causing the TCU to malfunction. thought i'd post the finding since i had only read about capacitors and resistors causing this shifting issue and nothing about diodes.

also, after talking to various mechanics we learned that the engine error code 43 can indicate a bad O2 sensor even though the code means fuel supply issue. sort of a weird yet fairly common glitch with this model of accord. replaced it and no bogging so far.