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Old 10-15-2012, 02:28 AM   #1
kerrn
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'92 Accord, TCU problems, D4 light stuck on

The D4 light is on all the time. I've been reading about TCUs and I've got mine out of the car to inspect it. Found 2 caps and 1 resistor burnt out. I replaced those along with all the other electrolytic capacitors and put it back on the car. It didn't make a difference. Then I checked a bunch of resistors and diodes from around the burnt caps. Reheated some solder joints, checked the connectors, the grounding. All looks fine. But the light is still on and the car is sluggish. Then I checked the solenoid connectors, the ground wires under the hood, the fuses (Is there a fuse for the TCU somewhere? I couldn't find it.) I found that some wires (from the ECU/TCU connectors) had the insulation chewed off by rodents (but they weren't shorting) and I masked those with electrical tape. I want to test the wires with a multimeter but I can't find a diagram anywhere. All I could check was the black (ground) wire.

The TCU is a 28100-PXO-A21-M1 (PXO or PX0?) and I couldn't find one like it for sale. On the other hand I'd rather DIY this because I'm short on cash after fixing a bunch of other things on this car.

Any tips, any ideas? What should I do next?
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Old 10-15-2012, 02:29 AM   #2
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Pull the TCU codes , they will pinpoint the problem for you.

http://cb7tuner.com/vbb/showthread.p...light=tcu+code

Could be a possibility that the electrical wires chewed off are not sending proper electrical power.
Another possibility is that the TCU is just done for. Try swapping in another TCU.

Last edited by TheFatMan; 10-15-2012 at 02:31 AM.
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Old 10-15-2012, 02:39 AM   #3
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Or get a salvage yard tcu
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Old 10-15-2012, 07:10 AM   #4
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Reman TCU doesn't have to be an exact match, if your car is 9091, get any 9091 TCU for your type of transmission. Same for 9293, just be sure to get an auto TCU. A reman unit is going to last the life of the car. My guess though is that the unmarked voltage regulator has a burned out center pole on your current board.
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Old 10-15-2012, 07:20 AM   #5
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Cloudsac has a diy on how to fix the tcu. Follow it and get a spair tcu and fix it with the diy just in case you beed it. Mine has been good for 6 months after fixing it.
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Old 10-15-2012, 09:26 AM   #6
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The D4 light being stuck on is indicative of an error code. The TCU is doing its job. Everyone assumes that when the D4 or S light starts acting up that they need a new TCU.

Take TheFatMan's advice, in the order that he gave it. What the other guys say is useful only if you find that you really DO need to repair or replace the TCU
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Old 10-15-2012, 11:01 AM   #7
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deev is right, my D4 came back after replacing the TCU, I had a faulty shift solenoid I had to fix or buy TCU replacements once a month. The solenoid from a JY was a cheap preventative fix IMO, but my TCU was so far gone that I had to replace 60% or more of the components to even get the codes. The previous owner liked to drive in 2nd gear only I guess. The longer the TCU acts up the more internal components it can harm.

I still have a spare reman TCU from fleaBay, just incase. I've also been working on a TCU replacement. I'll be ready to reveal that in the next coming months after some more refinement.
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Old 10-16-2012, 09:31 AM   #8
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Sorry about the delayed response, I'll be more prompt next time.

@TheFatMan, @deevergote: I shorted the blue connector, the D4 light stays solid on. The Check Engine light turns on too but it doesn't blink either.

@ryandavis33: I live in Europe and this car (especially the US model with A/T that I have) isn't popular here. I can't source parts locally, used or new, my only option has been to order straight from US. I am a bit wary about buying used salvage parts from abroad without the possibility of testing the part in advance. But at this moment, I don't know if I have a choice.

@wildBill83: Where do I get that '9091' number from? I'll get the TCU out of the car to check the voltage regulator. Are there more than one? If so, could you mark it for me on this image (I suspect it's the one with the heatsink)? I didn't take the solenoids out but I checked them with a meter and then with a battery and I think they're fine.

@10thAnnivCB7: Who is 'Cloudsac' or where is that DIY? Google didn't return a thing. I've read a few threads about replacing blown caps and resistors and I've tried that. Replaced all the electrolytic caps and two (15 ohm, if I remember correctly) resistors. I was hoping someone could point me to some other 'suspect'. Like wildBill83's suggestion of a faulty regulator.

Thank you all! I didn't expect so many comments. I've gotten used to other, less active, forums.
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Old 10-16-2012, 09:40 AM   #9
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When you jumped the blue service connector, what did you do next? The key should be in the II position, powering all accessories, but leaving the engine off. That is when the lights will flash the error codes.

As for the TCU repair thread, 10thAnnivCB7 was being lazy and didn't link to the thread he mentioned... and misspelled the member's name that he was referring to. You'll find the thread HERE



I should've realized you were from Europe. Your English is better than that of any American on this site! Are you in Romania?
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Old 10-16-2012, 10:04 AM   #10
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Do you have any appliance or TV repair shops in the area? A trained electric technician should be able to fix the problem. Also, did you check the diodes? I had to replace some diodes as well. The voltage regulator that killed my board is the one next to the failed caps/resistors in that photo. Is that photo of the inside of your board? By 9091, I mean 1990-1991 year models, I have found that the last couple of characters don't matter as they relate to a lot code 28100-PXO-???-?? should be what your current one looks like.

Also if you buy remanufactured, buy from a reputible seller with a return policy, don't buy a junk yard item because it will fail again. Always contact the seller and explain to them what you are doing.

I have both a working 28100-PXO-931 and 28100-PXO-722-M1 and they both work great in my 93 SE.
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Old 10-16-2012, 10:39 AM   #11
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@deevergote:
I followed that exact procedure but nothing flashed. I'm pretty sure I had a good connection.

Yes, I read cloudasc's thread. It's what made me check the TCU in the first place.

And yes, that's where I'm from. It took me a moment to realize that you're a moderator!

@wildBill83:

I checked some diodes and resistors from and around the path of the previously burnt components. None of the ICs or smaller ceramic caps though (I don't have a capacitance meter). I have a limited experience servicing electronics but I figured I'd do the easy stuff myself. I'll check that regulator and see how it goes.

That picture isn't mine, I found it online. From memory, it has an identical layout.
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Old 10-16-2012, 10:46 AM   #12
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I had to replace the miscolored thin film and cermic caps on mine as well, look for discoloration on them. Be careful, I pulled up a few traces when desoldering components and had to rebuild traces with 24AWG wire.

The first thing you should do after getting a TCU that will shift gears is to drive it for 30min and then try and pull codes again. You may get flashes then and may be able to diagnose if the TCU failed on it's own or something is drawing too much current and not operating correctly.

I believe I spent $50 USD replacing components on mine just to get it out of limp mode. My time + that $50 was easily worth the remanufactured unit I bought for $85.
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Old 11-03-2012, 07:07 PM   #13
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Quote:
Originally Posted by lfse View Post
Hey all,
My TCU was blown (and i'm no good at a soldering iron), i replaced it and now the car won't start... like the engine won't even try to turn over - which was never a problem before.
Am i missing something? I spent about two days going through the forum reading up on how to make the swap and it seemed fairly straightforward. I'm not super knowledgeable on cars, just good at following directions. Everything's hooked up just as it was prior to me taking the thing out so i'm just wondering if i'm missing some simple step to reset things?
Any help is greatly appreciated...
Good to see a newcomer that uses the search function, and welcome to the site. First thing I would check would be fuses, a fuse might have blown while you were doing something, and could prevent the car from starting.

If your car was able to start with the previous TCU, have you tried putting it back in, and seeing if your car will start? I don't think a bad tcu would prevent the car from cranking, but it is worth checking.

When you turn the key to acc, does everything come on like normal still? Do you see the check engine light flash on, and then turn off? Can you hear the fuel pump prime?
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Old 11-06-2012, 08:25 AM   #14
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In the future, please don't hijack someone else's thread. It is good that you search, but this discussion was about kerrn's car, not yours.
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