Help Troubleshooting FI Code (IAT 9 blink) 2003 6th Gen

Hey all,

Originally encountered this problem when VFRWorld was down and I couldn't post so I ended up putting it up on VFRD, and then was on vacation. So I'm back now and wanted to get your input on this. This is the copy/paste:

Just replaced the thermostat on my 2003 VFR (stuck open) ... dealt with the nightmare of throttle body removal and reinstall, all went well.

Turned the key to ON and, damn, FI code. 9 blinks - IAT. So, I proceed to troubleshoot the intake air temperature sensor problem... (for reference, manual page 5-21).

I have a feeling the problem is NOT the sensor but something much more expensive Because:

Resistance across the sensor is ~4k ohms at garage temperature. When warming it in my hand, the resistance drops to ~2.5k ohms. This seems to be working appropriately.

The line voltage coming in to the IAT sensor is ~11V -- which is twice what it should be according to the service manual. Load voltage coming out of the sensor is ~9V (hard to tell since the battery is old and discharges quickly) but it appears that the resistor of the IAT sensor is working properly.

So, I think I've got too much voltage coming into the sensor, and the bike is seeing the 9V coming out of the sensor and saying "uhh... excuse me IAT but the temperature is WHAT?! you're crazy IAT, I'm throwing a code!!"

And, if I'm correct, this line voltage is coming out of the ECM? So I broke something in the ECM.

Does my troubleshooting thus far make sense?

Where is the ECM located?

Do you know the part number for the ECM off hand? I can't figure out which "page" of the parts fiche to look for it in.

If I find a part-out, what year of ECM can replace the potentially faulty ECM in my 2003? Can I use any 6th gen or does it have to be a 2002-2006?

Thanks for the help!

The next step for me is going to be adding resistors in place of the IAT to bring the 11V down to ~3v to see if this turns the code off to make sure this is in fact the problem...

____


I then found the part numbers for the ECM:

38770-MCW-L03

Can anyone verify this?

Looks like it is the same for 2002-2005, a different part number for 2006+.

Side note, $600 is a quarter of what I paid for the whole bike :doh: If this is the only option, keep an eye out on the For Sale board for parting out a 2003 VFR800.....

____

I had been emailing with Meatloaf since he was kind enough to send me a new IAT sensor he had... while I haven't be able to test that just yet, I'm not thinking thats the problem. Meatloaf is thinking that the battery voltage is NOT coming from the ECM, but rather a short somewhere. He sent me a VERY detailed and informative email (THANK YOU!) about why he thinks this is the case, and I'll post that here once I get his permission, but the main gist of it was that it is more likely there is a short as opposed to a fried ECM.

So my next step is going to be yanking the TB's off, AGAIN (hey, at least I'll be good at it!!) .... and just untaping the wiring harnesses and searching for shorts.

So I guess I'm not really asking for any more help right now but rather just posting this up to document the progress. Thanks for looking

EDIT: Info Meatloaf sent me in email:

If you are testing per the Honda Service Manual, you are going to find a few things that make your life miserable in the testing. The first thing that you are going to notice is that the manual says that you need TWO of the special test harnesses that plug between the two connectors going to the ECU and break out into a separate connector for you to use your multimeter on. These are unavailable to the public. I talked to my Honda dealer and they are not available as dealer items only. My guess is they are only available overseas.

This makes doing some of your testing a little bit tricky but after some thinking I was able to come up with a method that works great. Since my mom is a seamstress, I used some of her sewing needles to probe the wires that I needed at the ECU. You can simply just push the needle through the PVC jacket of the wires and this gives you a spot to connect your multimeter to while the ECU is still connected.

With all of this being said, I think you are looking at a short somewhere. The 11+ volts that you are getting is more than likely NOT coming directly from the ECU but instead two wires that have rubbed against each other, one of them being one of the wires that goes to the IAT sensor. It will be a royal pain the the butt to track down as you will probably have to untape stuff all the way from the ECU to the IAT sensor. If you do untape all of this, you will more than likely be able to seperate the IAT sensor wires from contacting ANYTHING including each other at which point your voltage should go back into the correct 5V range.

The reason that I say this is likely the case is two fold. First is that the ECU is a solid state part that has no moving parts. It is simply a programmed chip. Second is that the electrical system only puts out a few different variations of voltage and those are 1.3V, 3.3V, 5V, and 12V. When something goes wrong with the programming, the voltage that gets put out is usually an extreme difference of what is supposed to be put out. The 11V or so that you are getting is probably more than likely due to a low battery. I would be that if you were to test this while running the bike at 5K RPM or while hooked up to a battery charger that you would find your voltage be be much closer to the 12V spec that is output to other sensors and various electrical components of the bike indicating a short between the IAT sensor and one of these components.

After verifying that is when you will have to figure out what wire of the ones taped up with it is causing the problem as it might not be so obvious. Once you find it you should have an easy fix on your hands, but it will just be a time consuming and tedious job.

I know the woes you are going through as I went through this for no less than three days on my VFR. I had the additional stress of it happening right before MotoGP weekend and trying to get it fixed before the race when it all came down to being a simple thermostat that threw all the codes I was getting.

All of this being said, keep your eye out on ebay for a used ECU for the bike. Keep in mind that ABS and non-ABS ECU's are different. One thing that I have NOT verified is if there are differences in the ECU between 02-05 and 06-09 models. I think that there were some changes made as I believe the 06-09 models know what gear the bike is in to allow for different fuel maps per gear and there was a change in the VTEC engagement/disengagement points.

 

Before you go rippng wiring harness apart, disconnect the connector @ the IAT and the connectors @ the ECM. If it is a short to battery voltage it should still be present and you will still be able to read battery voltage (11v?) @ your IAT connector.

 

Thanks I'll give that a shot! That would be the big gray connector, right? There is also a red 2 pin and a green 2 pin connector right there as well..

 

Haven't had mine down that far, I dunno man....

 

You can post up whatever ya want from me El.

Just because it is 12v doesn't mean it is coming from the battery. It could be one of the 12v lines coming out of the ECU shorting with the 5v line going to the IAT. You might still have to disconnect the connectors going to the ECU and test for resistance from one of the pins at the ECU to all the pins that go to the ECU. If more than one of them has no (or very little) resistance, then you know which two wires you need to look at. You could then trace the two wires and find out where they touch each other to find the short.

 

+1 Meat, forgot to mention that one......:doh:

 

Good plan! I will get on that this week. It's getting warm, and I need to get this bike out on the road!! :banana:

Also updated first post with the info you sent me via email.

 

It seems kinda coincidental this should happen immediately relative to your replacing the thermostat. So...and I'm not 'dissin' your work or anything, and I haven't done the job recently so I'm not remembering the exact procedure. But is it possible you have a couple connectors turned around? It might be a good time to check your work.

I know there is also a recall on this model relating to the reg/rect and replacing the front fairing subharness. Wouldn't seem to be related to your issue but then main harness heat damage isn't unheard of. Matter of fact I replace the main harness on one a couple years ago. You might want to give that bulletin a quick look.

 

I agree w/ dizzy ck all connections one has to be mixed up somewhere

 

I've been through it a bunch of times... I don't know how anything could be connected wrong since they're all unique plugs and can only get connected to their appropriate sensor/plug. Any ideas if there are two that are interchangable??

 

I've been through just about all of the connectors on the VFR and the only ones that are the same are for the lights and the O2 sensors. All the rest are unique in either pin count, keyed, or shape.

 

Hmmm well that might explain why flipping on my high beams shoots light out the back of my tail pipes!! :wink:

Still digging... it's finally getting warm in the garage. I'll keep yas up to date...

 

:doh::doh::doh::doh::doh::doh::doh::doh:
:doh::doh::doh::doh::doh::doh::doh:::doh:
:doh::doh::doh::doh::doh::doh::doh::doh:
:doh::doh::doh::doh::doh::doh::doh::doh:

Well........... I'm an idiot.

It actually was a switched connector. Apparently the IAT sensor plug is the same as the one that goes to some vacuum solenoid on the right side of the air box. I didn't even have that plugged in completely missed it. What a disaster. I think that solenoid has something to do with VTEC.

I got the first band clamp undone on the throttle body ready to yank them again and saw a plug staring me in the face that I didn't even have hooked up to anything. Yep, sure enough it was the same as the plug I had on the IAT sensor.

Anyway, thanks for all the suggestions and help, thanks Meatloaf for the IAT sensor I guess I have a functioning IAT sensor I have no use for. I'll pay it forward to the next guy with a problem!!

Thanks again all I really appreciate all the support and information!

 

Actually I think that solenoid is for the evap canister and emmisions. It is what lets the gasses from the evap canister enter back into the airbox.

Glad it all worked out for ya. I thought the plugs were keyed differently but was wrong. Get out there and ride!

 

Yep. Bypass control solenoid valve.



The electrical connector that goes to that unit is the same setup as the IAT sensor.

I promise I'm not as shitty of a shadetree mechanic as this thread makes me seem :doh: lol

 

congrats... no strip all that crap off so you dont need to worry about that again.
ops my bad your still waiting on me to make my plates...

 

:vtr2: yep!!

 

You're not an idiot. Nothing bad happened. You didn't blow up anything. The machine was trying to tell you that you missed something but as many of us do, you had convinced yourself that that was impossible. As many times as that has happened to me you would think it will never happen again, but it probably will. Heehee. The bright side is now you know and next time something similar happens, you will most likely remember this little incident

 

I still feel like an idiot. lol

But yes nothing blew up... yet at least...

What does a machine know that I don't! A lot, apparently.