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Richard, Motorcycle Mechanic
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Experience:  Senior Mechanic & Technician
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2004 Honda Fourtrax TRX400FA. Flashing Code 12, performed

Customer Question

2004 Honda Fourtrax TRX400FA.
Flashing Code 12, performed all recommended testing as indicated in the manual. Replaced the shift control motor, traced the continuity and voltage of the wiring, and also replaced the ECM.

Still flashing Code 12. Also have the 4X4 light flashing 4 times indicating a "system voltage" issue.

Nobody, including Honda dealerships, have been able to help.

Maybe you can????
Submitted: 7 years ago.
Category: Motorcycle
Expert:  Eric replied 7 years ago.


testing with the voltmeter, on the battery terminals. what is the highest charging voltage you get while reving the motor?

Customer: replied 7 years ago.

I haven't tried that. I will give it a try this week and get back to you.


The battery seems to be charging well. What type of response would I be looking for and what would it indicate?


Ie...under 14volts might indicate...? Is this a way to tell if there is a short to ground?

Expert:  Eric replied 7 years ago.
im looking for a very high voltage, like beyond 15 volts. 13-14.5 or 15 is normal. but anything that touches over 15 is an overcharge and i have seen it happen on this atv before. ill await your results.
Customer: replied 7 years ago.

Could this be why my winch, which is directly wired to the battery, only works intermittently?


Another note I should make is that I keep blowing the 30 amp control motor fuse. I have bridged the fuse temporarily because I kept going through fuses. I would assume that the shift control motor is drawing too much voltage, but it doesn't even actuate when I try and do the reinitialization process.


It's odd because sometimes the machine will find neutral, but as soon as I put it in gear it goes right back into limp mode.


Frustrating as all hell!

Expert:  Eric replied 7 years ago.
blowing the 30amp fuse just may confirm my suspicion on this. but no the winch being on the battery is totally fine. in fact it would be best mounted there then anywhere else. i dont believe that would be causeing all of this. now really interested in that charging voltage!!
Customer: replied 7 years ago.

Ok, so I checked it tonight.


When idling without the lights on, it was registering at 16.9 volts. When I revved the machine it went up over 17.5 volts.


When the machine was idling with the lights on, it was registering about 14.0, but when I revved the machine it went over 15.5 volts.


So, now that we have proven your hunch, what do I need to replace now? Sounds like the voltage regulator which is right behind the ECM?

Here's my conundrum, if you are right on this, will the machine really work fine? Possibly right? Funny that the machine was throwing the 12blinks code, which seems to be completely erroneous at this point.


If this works, I certainly have NO PROBLEM paying you for your help.


Fingers are crossed, let me know what you think.



Expert:  Eric replied 7 years ago.
Yep, definately overcharge. Yes your atv should work properly after replaceing out that regulator. When the ECM is sensing the differentcomponents it does this by resistances, and voltages. Each has their range of operation or what the ECM determines what is wrong. And that goes for values high and low. And this will throw codes accordingly. I'm sire you find some results with this.
Customer: replied 7 years ago.

I'll get the part on order, install it, do the reinitialization, and if all is well, I'll certainly hit the ACCEPT button and get you paid. Might throw in a bonus too (if possible) if this is the fix FINALLY.


Thanks again - I'll be in touch shortly.



Expert:  Eric replied 7 years ago.
Great, I'll await your results.
Customer: replied 7 years ago.

Hi Eric,


Sorry I've taken so long in getting back to you on this. I actually ordered the rectifier this week, and hope to have it installed this weekend. As soon as I get it installed and *crossing my fingers* if the issue is resolved, I'll be sure to hit ACCEPT and get the funds released.


Thanks for your patience.



Expert:  Eric replied 7 years ago.
ok no problem, just let me know how it all turns out, thank you for the update
Customer: replied 7 years ago.

FACCCKK.....still no good. The machine will not exit limp mode and code 12 is still flashing. I replaced the rectifier with a new one, still no dice.

I tried the initialization procedure, but it will not actuate the shift control motor. It just reverts back to code 12. I've had a few private messages from others who have this mysterious problem and have not solved it, having done the same things I have.

Now what?

Expert:  Eric replied 7 years ago.
What is the charging voltage mow?
Customer: replied 7 years ago.
Hmmmm....I didn't check that, as I assumed all would be ok given the new rectifier. I'll have to get a voltmeter again and check it.


BTW....if it's still not ok, then what?
Expert:  Eric replied 7 years ago.
i was just makeing sure the voltage went down. the code twelve only meant one of two things. if the voltage is back down to a good running voltage. it would be safe to say that the ecm might have gotten fried from the overvoltage. but ill reserve that till we take a look at the charging voltge.
Customer: replied 7 years ago.

Hi Eric,


I tested the voltage when running again, and it ranges from 14.9-15.5 at idle, lights on/off, and when revving. Obviously the rectifier was a culprit.


I have a quote in ebay on another used ECM from a machine being parted out. Trying to save a few bucks given my past expenditures to get this machine running properly.


I'll touch base when I get it and get it installed.



Expert:  Eric replied 7 years ago.
great. would love to hear this atv working.
Customer: replied 7 years ago.

You and me both ....haha.


I'll hopefully have it within 10 days, and it's easy to install. Man-o-man.....if it's not the ECM at this point, then I'm really stumped.


We'll see how it goes. I'll be in touch when I get it installed.



Expert:  Eric replied 7 years ago.
ill await your results. good luck!
Customer: replied 7 years ago.

Hey Eric. Wow - too long since my last post. I just received the new ECM about a week or so ago, and installed it tonight.


Exact same symptoms as before. Goes right to 12 flashes. Cannot do the initialization procedure because it will not "find" Neutral.


Thoughts? I'm guessing I have 3 good ECM's at this juncture given that I have 3 and no symptoms have changed.



Customer: replied 7 years ago.
Hi Eric,

Hopefully you are still around? I'm not sure how much I promised to pay you to help figure this out, but I'm willing to "up" the fee given the long drawn out process.

I had another observation last night, as I've had some time to look at it. There are 3 sensors or switches just inside the left side engine cover, which detect the D/N/R position. I noticed that one of the connections was severed inside the boot. I stripped the wire, and made the connection again.

Now, when I turn the ignition on, holding down the UP/DOWN shift keys, it will show the shift position as " - - " and it just blinks slowly. If I start the quad, it is almost in a semi-limp mode. I have full reverse - which I've not had since I got the quad. I have one gear forward. Nothing shows up on the heads up display for ESP or auto mode, the " - - " just flashes slowly. I think I need to trace all three connections for continuity between the connector and the ECM plug just to ensure there isn't a short on one of the others.

I tried to perform the initialization sequence, but it still seems that the machine cannot find Neutral. If it could, I think the initialization process would be fine.

I think it's a step in the right direction.....I feel like we're closer to resolving the issue. Oddly, if I just start the machine normally it goes into the Code12 limp mode, but I'm certain it's none of the shift control motor circuitry due to having checked all circuits and replaced all components. I think it's still an erroneous code due to other issues.



Expert:  Eric replied 7 years ago.
i believe those have a seperate neutral light, and reverse light, do those appear to go on and off now?
Customer: replied 7 years ago.
Yes, the neutral light and reverse light are separate. They do go on and off when I move it in and out of gear.
Expert:  Eric replied 7 years ago.
that harness being cut brings up many questions. with that being found, investigating that area as much as you can for any other signs of breakage can help. the tests and such that i have mentioned have all assumed that wiring is ok. being that most commonly wire breakages are not common on these. if you cannot find any other breakages, i can help with a series of tests with an ohm meter to see which wires have continuity with each other and that helping finding out why you keep getting this code. these can be a little tedious, but ill be happy to help with those if that is an option you would like to explore. thanks
Customer: replied 7 years ago.

With the code 12, I verified all the wiring for the shift motor circuit. I've not verified any other wiring. Given that the machine seemed to not be able to find Neutral, I started looking for other options related to the shift positioning/switches. I found a recommendation on which shows the switches and to test for continuity. I've not done that test yet, but I intend to this week for sure.


I don't know if you are able to manually reposition the shaft, or whatever the switches correpond with, to make the machine see Neutral again? I find it very interesting that I can get the machine to start the initialization, but as soon as the machine needs to show Neutral, it fails. Before that, I can start the machine, and now I have full Reverse and 1 speed forward. No gear selection shows up on the heads-up display though.....


Any recommendation you may have, I'll do my best to perform.





Customer: replied 7 years ago.

Hey Eric,


Do you have recommendations on what tests to perform with a multimeter?

Customer: replied 7 years ago.
Customer: replied 6 years ago.
OK....I'll pay anyone else willing to help out with this issue?
Customer: replied 6 years ago.
It would appear that I've stumped the experts.......
Expert:  Richard replied 6 years ago.
I am not stumped on this one. Not yet any way.

Do you have a little more time to spen on this ?

What is the battery voltage with the igntion switch off, then with the igntion switch on.

Then give me battery voltage with the igntion on, run/stop switch set to run, press the starter buttton for 15 seconds ( at this point the engine should be turning over) record te lowest battery voltage you see.

Start the ATV. What is the battery voltage at idle. 1/4 throttle, 1/2 thorttle, 3/4 throttle and full throttle. You should record each reaching after 5 seconds of reaching the point.

Now what code do you have right now ?

Have you tried to erase the codes ?

please write in complete sentences.

Check the 30AMP fuse in the fuse box, is it blowed ? You can check the fuse by settin the meter to OHMS which is resistance.
Customer: replied 6 years ago.
HI....thanks for the email.

I will have to try this with a voltmeter, as you've outlined.

I'm still getting code 12. I think it has to do with the N/D/R sensors, or possibly the shift linkage at this point. At times it will "find" Neutral, but not for long.

Finding Neutral is what's preventing me from reinitializing the machine I believe.

Can you tell me how to erase the codes?
When I hold the UP and DOWN error, I turn the key. I then press UP, DOWN, UP, and the shift indicator shows a slow blinking "--". This way, I can use reverse and 1 gear forward. Otherwise, I simply get limp mode if I just start it.

Thanks for the recommendation, I'll try it when time permits.

Expert:  Richard replied 6 years ago.
I have posted the diagram below to erase the codes you are seeing.

Do you not have a service manual ?

Have you done the initial setting procedure ?

I have posted the erase procedure and the initial setting procedure since you have replaced the ECU. If it fixes the ATV, please press accept.

Please update me. I like to work on the problem quick and find the problem, the more days you wait, then the longer it will take as I keep my mind set on your question..

Customer: replied 6 years ago.
I do not have a service manual, sorry.

I will try erasing the error code and the initialization procedure again.

If it works, I'll definitely press the "ACCEPT ANSWER" button.

Expert:  Richard replied 6 years ago.
That will be fine, when can I expect you to return with the results. I would like to solve this today, as it is the last day of the month and I try to close all my questions out and take care of the customer. If the procedure doesnt work, please repsond with the readings I have asked for. I have a good feeling that it will work.

Please make sure that when you click or if you do click accept, that you accept from the correct expert.


Stay warm

Customer: replied 6 years ago.
It won't be today that I get to try it, but likely through this week I'll get a chance to have a look.

I'll be sure to get back to you right after I try the steps recommended.
Expert:  Richard replied 6 years ago.
I have just looked over the information you have provided regarding the 30 AMP fuse blowing. This usally blows when the vehicle has seen alot of water and/or the control motor is fried.

I have some more porcedures as we progress Ill give those to you. I dont want to get to far ahead right now.

If I think of anything else I will post it, just make sure to get me all readings I ask for.

The below doagram goes along with the initial setting procedure as I see it dodnt load in the other post.graphic

Edited by RACETECH on 11/30/2010 at 6:55 PM EST
Customer: replied 6 years ago.
I already got a new shift control motor, and installed it.

I can't comment on the water immersion, as I bought the machine used. I can comment that the undercarriage was impeccably clean and in excellent original condition. Same with the plastics. It was used primarily on a farm. It hasn't been ditch banging much, if ever.

I can check the 30A fuse again, but ever since I replaced the voltage rectifier, it hasn't blown to my knowledge. I'll check though.

Thanks for your help, glad to see someone is still interested in addressing this Honda Fourtrax enigma.

A bonus is in store if we get this thing fixed!
Expert:  Richard replied 6 years ago.
we will fix it