91 Accord LX/Automatic W Sports T/ TCU Problem? - Page 2 - Honda Accord Forum - Honda Accord Enthusiast Forums

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Old 05-26-2011, 07:41 AM
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Default More Info & Car At Mechanics

Proud to report my car is in the shop and per the reccomindations of this posts, he is going to check for the codes.

This is after the orginally described problem now has completely prevented the car from starting!

Since I also have done some research on the AT TCU. Per the information I found, I tried the disconnecting the battery (in desperate attempt to get it started so I could get to the mechanic) and wouldn't you by doing so reset the unit and the car started right up.

I will post the codes that we get to complete my thread. After I post the codes I plan to discuss the fix solution and will post what we determine.

Check this link out for some interesting information (ALONG WHAT POSTERS HAVE SAID; JUST MORE DETAIL AND DIAGRAMS)

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

Copied & Pasted Text From Link

The 90-93 Accord is a modern vehicle that relies on the computer to determine shifting points to increase comfort and safety. Without the computer the transmission won't shift and the car will simply move at a snail's pace or will simply default to limp mode, which can either be 2nd, 3rd or 4th gear. For example, a faulty transmission computer could cause the car to suddenly shift into lower gear while driving. This causes the car to drop in speed while the RPM shoots up. With other cases, the car will have a hard time accelerating from a stop unless the car is first manually shift to D2. The symptoms are followed by the 'S' or 'D4' shifter status light on the instrument panel blinking, or lights up or doesn't light up at all.
If the car won't shift into correct gears and displays a self-diagnostic light most likely the fault is not with the transmission. Sometimes a clattering sound may also be heard in the cockpit. This may be the sound of the transmission interlock system misbehaving, which may indicate a bad TCU.
Do not replace the transmission without first confirming the situation electronically. The fault is usually the Automatic Transmission Control Unit (also known as the automatic transmission computer or TCU/TCM.)

If there is a problem with the input or output in the A/T control unit the D4 or S light in the gauge assembly will blink. However, some PGM-FI problem will also make the D4 light in the gauge assembly blink. If there is a problem with the emission fuel control system the code will have to be retrieved from the check engine light first. Repairing the emission fuel control system is first priority. After repairing the PGM-FI system then reset the A/T unit's memory.

Problem: The usual problem with the Honda Accord transmission, namely the 90,91, -, - Accord, is a bad transmission computer. What happens is that the transmission computer has a couple cheap parts that fail. The failing parts may or may not automatically put the TCU into a saftey (limp) mode (aka, the "fail safe strategy.") The three known failed components are two resistors and a capacitor inside the transmission computer. The symptoms are of several types. The car "S" light or "D4" is on (just stays on D4 no matter what gear is selected) or blinking and the transmission won't shift into any gears or sometimes stuck on a certain gear. The trouble codes could be 1,2,7,8,9,15 or None. Shifter interlock control unit buzzes. When the driver steps on the gas the rpm goes high but the car refuses to move at the expected speed. By resetting the TCU, either by removing the fuse for a certain period or by disconnecting the negative battery for 5 to 10 seconds will eliminate the problem, but only temporarily.


The resistors R41, R42, R43, are overheated or burned and capacitors C27, C28, C32, C33, C5 leaking or shorted. Some resistors will be burned off to the point where no one can determine the values. A common sense approach is to consult a working TCU and read the color code on the resistors or start with the highest resistance and go down. Find the best wattage resistor or the best voltage capacitor that can fit.
The problem originates with the electrolytic capacitors leaking. Often, the capacitor short circuits frying other components such as your resistor. Another words, the burned resistor is a result of another component failure, namely the capacitor. The fix is to replace the bad parts. See the values below.

Parts values: R41 is most likely 15 Ohms; R42 is 15 Ohms, both appears to look like a 1/4 to 1/2 Watt; Capacitor C28 105`C 220uF 35V Nichicon H9146. Replace all of them or else the problem may return. If the problem returns, it's likely not your solenoids, but the parts on the circuit board.

sample: Before it was new and now it has fried.
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Old 05-29-2011, 07:23 PM
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Default Update: Mechanicís Report

So I went to take my car to my mechanic after discussing the TCU and ECU and wanting to get the codes as suggested. The night I went to take it, my car wouldnít start and my green S light ever so flashed as it normally does. So I decided like I normally did to try and start it, let it sit, then try again later, as it usually starts. Well after trying a couple of times a day for 3 days, still not starting. Frustrated wanting to get it to the shop, I decided to try to disconnect the battery to trip the computer. NOW I know it clears the error codes but I decided I already knew all the symptoms of the problem. I did so and it started right up. I drove it around and the speedometer started going goofy, the green S lights started flashing as the car seemed to shift down a little, but it ran fine. I drove around for a while to hopefully get some new error codes logged. I then delivered my car to my mechanic.

After a day I contacted my mechanic whom asked how I got the car to him (I told him it wasnít starting and I would get it to him right away.) I told him I disconnected the battery and drove around for a while to hopefully log some new error codes.

He said he was unable to get any ďhard codes.Ē He said he tried to get codes before about 6 months ago and didnít even get codes then. He also said he couldnít hear the fuel pump at all and felt it was bad or the main wire going to it could be going bad (as I asked if either was bad how did I get the car going all the time and got it going after disconnecting the battery just a night before.) Lastly he added there was some oil in the intake tube going into the carbonator air doctor-oil comes from the ďrigs.Ē

-What I Think Is Wrong With the Mechanicís Report
As I have mentioned I am NO mechanic and I am actually uncomfortable even making a guess. However what I have read and gathered from other sources seems to contradict the mechanicís report. Donít get me wrong he is a nice older gentleman who has helped me in the past, either we are communicating properly or just arenít on the same page.

I find this extremely hard to believe. How in the world both times do you not get codes when the car performs all the classic symptoms of a bad TCU? At that even if I cleared the codes how do you determine despite the known symptoms that itís the fuel pump? I swear I could hear the fuel pump when starting the car. I could even smell gas sometimes when trying to start the car.

I kind of think perhaps the fuel pump relay could be bad which from what I understand could be determined by Check Engine Error Codes. Also if the relay or wire is bad how did/does it start and I was able to drive it?

Itís an old car. I am surprised I havenít found oil leaking from the ignition!

-What I Think Should Be Done (Based upon what I have read and learned.)

1. Try again for error codes. Follow the codes.

2. Also remove the TCU and open it up. Look for signs of leaking capacitor or burning of the resistor.

3. Inspect fuel pump main wire (same as fuel relay?) Check the check engine codes.

As far as no codes, the only thing I have read is, 1. the shift valve solenoid is stuck, weak, or needs replaced. 2. No codes and line pressure confirms so, then a valve body is stuck. 3.Replace main relay will also solve the blinking D4 light.

-Parts Shopping Question:
Also is the TCU and the ECU the same thing/box. From the repair articles I read it seems to treat it as separate units. However some are referring it to as the ECU/TCU. Could someone please clarify these for me?

Sorry for the long post, but I figured the more details, hopefully better. Thank you all very much again for even just taking the time to read my narratives. Any feedback is greatly appreciated. I hope everyone had a great holiday weekend.
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Old 05-29-2011, 07:24 PM
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Default Interesting Link

For the sake of this post, I found this link I thought I should post on repairing the TCU. Has really great photos I thought.

1991 Honda Accord Transmission Control Computer Unit Repair
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Old 06-01-2011, 06:06 AM
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Default Voltage Reading

What kind of reading should I get if we test the fuel pump relay and the fuel pump with a voltage meter?

Our plan of attack is check fuel relay fuses, main relay, and fuel pump, to get some readings (hence needing the numbers.)

Then we are going to ignore the mechanic's computer hook up and go ahead and paper clip test the check connector to get some codes.

This will give hopefully where we are at. REALLY HOPE we find out something. THANKS!!
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Old 06-05-2011, 09:36 AM
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I have been on vacation and behind in responses.

Check fuel pump by 1) listening and 2) 12V to the pump power supply wire in the trunk (yel) for 2-3 secs, then 0v (mfr opens).

If no voltage supply, then check MFR voltage supply (blk/yel) for 12V. If good, then new MFR or repair MFR.

Generally, MFR and fuel pump problems do not cause ECU codes to be set.

good luck
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Old 06-05-2011, 07:06 PM
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Originally Posted by TexasHonda View Post
I have been on vacation and behind in responses.

Check fuel pump by 1) listening and 2) 12V to the pump power supply wire in the trunk (yel) for 2-3 secs, then 0v (mfr opens).

If no voltage supply, then check MFR voltage supply (blk/yel) for 12V. If good, then new MFR or repair MFR.

Generally, MFR and fuel pump problems do not cause ECU codes to be set.

good luck
Hope the vacation was nice....

Do you think it could be both 1) something with the fuel relay 2) the TCU - since I have classic TCU problems? It just seems we have symptoms of both..??

Also have some other conversations been involved in regarding this issue. will post them for reference.
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Old 06-05-2011, 07:10 PM
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Well, first you would want to check the fuel pressure after the pump as the pump is running with a [COLOR=orange !important][COLOR=orange !important]pressure [COLOR=orange !important]gauge[/COLOR][/COLOR][/COLOR]. You could also measure the volume of fuel the pump is able to move from the tank. Sometimes manufactures give volume specifications for that.

If fuel pressure is low or no existent, that is when you would probably do some voltage measurements. If the fuel pump isn't running, you would want to check power to the pump at its [COLOR=orange !important][COLOR=orange !important]connector[/COLOR][/COLOR]. It should be [COLOR=orange !important][COLOR=orange !important]battery[/COLOR][/COLOR] voltage, when the fuel pump relay is turned on. If you don't have voltage to the pump, you would chase the circuit to the source to see where it is open or excessive resistance is hiding.

If the voltage to the pump is there when the relay is energized, you would check the ground circuit. The ground is just as important as the power side of the circuit. Any excessive resistance or opens in the circuit is going cause a slow or a non moving pump.

If you have power and ground to the pump, the best way to check the circuit integrity is to voltage drop the circuit. [COLOR=orange !important][COLOR=orange !important]Voltage[/COLOR][/COLOR] dropping checks for excessive resistance in connectors, wiring, and switches. The circuit has to be powered up to perform voltage drop tests.

Read this great article:
MOTOR Magazine Article | MOTOR Information Systems


You know, the more I think of it and wonder, and I beleived I may have mentioned in my orginal post, is that something with the fuel relay system could be just it. Reason I say this is because when my [COLOR=orange !important][COLOR=orange !important]car[/COLOR][/COLOR] is in park running, its like it is sputtering and or idioling really low-like its choking or something. You would think its its plugs, wires, cap & rotar but I had all that replaced. Also sometimes when I went to start it, it would fire and trying starting and fumble some and I had to hold the [COLOR=orange !important][COLOR=orange !important]gas[/COLOR][/COLOR] in. Even then at times it would fumble, then I wouldn't be able to start it at all. After a few minutes I sometimes got it going and it ran like it normally did, with that green "S" light flashing away.

So we could be missing power or have a bad ground.

Interesting article. I downloaded the PDF of it and printed it out. I am going to show your post and the article to my motor head cousin. My trusty old mechanic was hospitalized so we are going to get to it here soon. I am going to send my mechanic a Get Well Card and a Thank You Card. Thank You Card? When I was a little kid I told him I thought it would be cool to be a mechanic. He set down his tools and spoke very directly to me and encouraged otherwise.
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91, accord, auto, flashing, gear, green, honda, light, lx, part, problems, resistor, resistors, sports, start, tcu

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