MIL29 IACV Intermittent problem

[veloman]

My 2011 NT700VAA with 59K miles on the clock has suffered an intermittent and infrequent MIL29 IACV fault for some years. This problem has gradually become more frequent to the point I have had to do some investigation.
All indications so far have been that the problem is a wiring problem around the area of the ECU. But all checks on the wiring as per the workshop manual suggests the wiring is sound. No problems show up with my multimeter even when giving the wiring a vigorous vibration test. I am now wondering if I have a problem with poor connection between the 33 pin plug and ECU in spite of liberal doses of contact cleaner,

Some questions for you knowledgeable folk over there

Is it possible to buy a 33 pin plug as used on the NT700?
Is it possible to depin the 33 pin plug as used on the NT700 and if so how?
Could a sticking IACV throw a MIL29 fault?
The “B” plug on my ECU has a metal “chastity belt” that prevents its removal, why does it have this (No mention of one in manual)?
How is this “chastity belt “ removed apart from cutting it off as the nuts are dummies and the bolt looks like an allen key head but isn’t (just a round recess)?


The last couple of times I’ve tried the bike, before riding I’ve checked all four wires to IACV and they look sound with no shorts or breaks, I see the correct resistance, around 107 ohms of the IACV coils on each pair of wires and repeatedly turned the ignition on without a MIL29 showing, I get half a mile down the road and the MIL 29 comes on!
Any suggestions welcomed!

 

[rc_heli_nut]

If you checked all the wiring, and it sounds like you did, it's likely you have a failing iacv motor. Not a common problem on Hondas in general, but I've put a few on older Accords.

You did not state your location, but here in USA the part is available from Partzilla, part# 16430-MEW-921. Clean the housing on the throttle body thoroughly before installing the new part.

Not sure what to tell you about security strap on ECM, my NT didn't have one, I suggest leaving it alone as it's likely the problem is not there.

 

[veloman]

Thanks for the reply and for my sins I live in the UK. I'm not planning to remove the B plug, I seem to have caused enough problems by trying to get to the bottom of the problem which has involved multiple unplugging of the A plug and which has definitely led to a more permanent MIL29, I was just curious as to its purpose and why some seem to have it and others don't. I asked the question about the IACV because that is something that I haven't checked by removal or replaced. I'll bear your comments in mind when I can definitely rule out any problem at the ECU end. The reason why I still suspect the problem lies at that end is.....
Last night I went out and turned on the ignition, MIL29 was present. I removed the ECU from its holder and let it hang horizontal on its cables and turned on ignition, MIL29 was cleared. I have previously gone through this action and have had exactly the same results and returning the ECU to its normal position brings back the fault yet when I check the wiring with the plug in any position it checks OK. At the moment I can only think I have some sort of a problem between the plug and ECU which hasn't been cured by use of contact cleaner.
I have just found a seller on eBay who sells a plug very similar but which comes up as not suitable for NT700. I'm awaiting a reply to see if he has a suitable plug or if the pins he sells are compatible.

 

[rc_heli_nut]

Last night I went out and turned on the ignition, MIL29 was present. I removed the ECU from its holder and let it hang horizontal on its cables and turned on ignition, MIL29 was cleared. I have previously gone through this action and have had exactly the same results and returning the ECU to its normal position brings back the fault yet when I check the wiring with the plug in any position it checks OK. At the moment I can only think I have some sort of a problem between the plug and ECU which hasn't been cured by use of contact cleaner.
I have just found a seller on eBay who sells a plug very similar but which comes up as not suitable for NT700. I'm awaiting a reply to see if he has a suitable plug or if the pins he sells are compatible.

Well, that changes the diagnosis a bit. For now, hold off on replacing the iacv motor. I suspect a previous owner or tech may have damaged the harness pins, at least on the one ECM connector you unplugged. I ran into this a lot as an auto service tech, where a previous diagnosis was attempted and T-pins or paperclips were used to probe the connector, causing damage to the pins, which now have intermittent contact with the ECM pins. Flexing the harness, as you did by hanging the ECM temporarily restores continuity as the wires and pins move.

Unfortunately the only good way to fix this is to get a Honda connector pin release tool for the harness, and pull the pins out one at a time from the connector shell and attempt to re-shape or replace the pins. It's also worthwhile to check the crimps where the wire meets the pins, the wire strands can get cut by test pins shoved in the wire-side of the connector shell.

I worked at a couple new car dealerships, and witnessed techs having to replace entire vehicle body harnesses because someone damaged the harness in this manner. Of course, you have to remove the entire vehicle's interior to do this. Not fun!

Sorry for the long post, but hope this helps you with the fix.

 

[veloman]

Thanks very much for your input. I think you may well be correct and that I may well be the "tech" with the paper clip! I confess I have used these although I was very careful not to push them in hard. The problem has certainly become worse since I started checking the wiring which was when I used the clips. I had kind of got round to thinking that I would have to look at removing the pins to inspect further and have been looking at various Youtubes on pin removal. They suggest that it is possible to do with a thin screwdriver applied in the right place although the last thing I want to do is damage the plug further and I'm a bit apprehensive without fully understanding the correct method for this particular plug. I'll look into getting a pin release tool. Thanks again for your help.

 

[rc_heli_nut]

I would not use a screwdriver to remove the pins, it damages the latches in the plastic shell, then the pins don't stay in place.

The pin removal tools are a thin rolled metal sleeve, with a handle, that unlatches the pins the right way. A quick web search turned up many choices for removal tools, you may have to buy a universal kit to get the right one for the ECM harness.

 

[ARKNT]

First good luck with your problem. Those intermittent problems have always been the most difficult for me to repair. Usually takes a while. Try to be meticulous in your efforts.
It sounds like you've done it but I would look very, very closely at the connections there at the ECM. Use lights, magnifiers to help if needed. The ECM doesn't fail often so that increases the odds of a connection issue. A poor intermittent connection may be quite difficult to see or measure.
Keep us posted on your results.

Arknt

 

[veloman]

I will certainly let you know how I get on especially if I find the cause of my frustrations!!! You are right, I need to take a really close look at the connections and will do after I've had a few days off to clear my head as I am just going round in circles now doing the same checks with the same results.
I've ordered what might be the right plug from China, at £2.35 I thought I'd take the chance. If nothing else it might enable me to work out how to take the plug apart so that I can remove the pins to make a closer inspection. Its going to take 36 days to arrive though!
Another thing I thought I might try to get me out of my continual circling would be to remove the IACV and see if the motor spins when it throws up the MIL29. I'm not sure yet what that might tell me but it would be a bit more information. I have tried listening for the beep that the manual says should be heard when the ignition is turned on but I can't hear anything even when there is no MIL29 returned. The fuel pump makes too much noise at the same time.

One thing that is puzzling me is that on the occasions that the fault has come on as I was riding along it never goes off on its own. At the very least it needs the ignition to be turned off. Then on occasion the fault disappears, on other occasions it needs the wiring around the ECU to be jiggled around to clear it as well. I'm wondering if the ECU only needs to see a momentary "glitch" in the IACV or its wiring to throw up the alarm and then latches with the alarm on until the ECU is reset by cycling the ignition.

 

[rc_heli_nut]

One thing that is puzzling me is that on the occasions that the fault has come on as I was riding along it never goes off on its own. At the very least it needs the ignition to be turned off. Then on occasion the fault disappears, on other occasions it needs the wiring around the ECU to be jiggled around to clear it as well. I'm wondering if the ECU only needs to see a momentary "glitch" in the IACV or its wiring to throw up the alarm and then latches with the alarm on until the ECU is reset by cycling the ignition.

You are correct, and the glitch that the ECM needs to see to set a code is likely to be the open circuit that intermittently occurs at the harness near the ECM. The NT's ECM is not that sophisticated, so for a motor circuit like the iacv, setting a code for that circuit may be limited to obvious failures like opens/shorts. In other words, the ECM is likely not able to set a code for a iacv performance concern, such as high/low idle. Modern cars can, but the NT is not a 2023 Honda.

I assume under normal conditions, the iacv is working, since you did not mention idle speed concerns. On a cold start, with the bike idling in neutral for a few minutes, does the idle speed get brought down as expected as the engine warms?

I think you are on the right path, and you'll find a damaged pin or two at the connector shell. Keep us posted.

 

[veloman]

Thanks for the explanation and I'm glad the NT isn't too sophisticated. At the moment I wish the NT had all the sophistication of my Velo, just a magneto and dynamo to worry about!!

When I've to turn on the ignition without getting a MIL29 I have started the engine and it does indeed drop revs as it warms up as normal. Then thinking the problem is fixed I ride it down the road and up pops the MIL29!
If the MIL29 comes on with the engine warmed up the bike seems to behave normally. If it comes on with the engine cold the revs stay high even when the bike has warmed up which is real pain to ride as tickover and gear changes are affected.

I'm pretty sure I need to somehow remove the top part of the plug (where the wires go in) before I can even think of removing pins. I've had a try and lifted the top part slightly but it seems very tight and I'm wary of trying too hard without knowing if I'm doing the right thing. Here's a couple of pics of the plug in case of any tips

 

[rc_heli_nut]

The top part of the plug holds down the silicone seals around the wires, there's usually a way to release this part of the plug, look for some lock tangs between it and the main piece. A small thin screwdriver can probably be used to release top part.

You'll need to get the silicone seals slid up the wires to get the pin release tool in there.

 

[veloman]

Thanks for the info. I found a plug on eBay UK that looked like it was the right one but the listing of suitability indicated not suitable for NT. However seller reckons it is suitable from photos I've sent him of the NT plug so I've ordered one. Hopefully seeing the pins when it arrives will enable me to locate the correct pin release tool and make some progress.

 

[veloman]

Plug has arrived and its the right one! I now understand how the wire end of the plug comes apart and have been able to do that on the ECU plug albeit with some difficulty as the wires resist moving the end cap and silicone moisture barrier very far away from the plug. I've also found that the front part of the plug similarly comes away to reveal square holes instead of the round ones in the front cap and have done this on the new plug but not yet on the ECU plug of the bike. Looking at these square ends I can see a plastic tag that must lock the pins.

On the photos of one of the new pins two small projections can be seen that I'm sure must engage on the tag in the body.

What I haven't worked out yet.
Is the pin removed by inserting a tool from the rear or from the front? The logical way to me would be from the rear and lifting the tab clear of the pin projections but looking at the ECU plug with its wires in there seems very little room to insert a tool whereas from the front there would be.

And why two projections on the pin to lock it? Are there two tabs in the body and does the right tool lift both?

Not knowing what shape of tool I need I've ordered a bunch of 36 in the hope that one will be the correct one. Does anyone recognise the type of pin and method of removal?

Thanks in advance for any info. and apologies for my lack of knowledge but this is all new ground for me.

 

[rc_heli_nut]

The locking tangs on the pins are visible in the pictures you posted, on the right side of the pics. So the pin release tool would be inserted wire side of the connector shell. Once the pin is released, remove pin and tool together.

Put some Isopropyl alcohol on the silicone seals to move them up the wires. Un-tape the harness to gain more room if needed.

I would attempt to re-shape the existing pins first, if you concentrate on the 4 wires for the iacv only, this shouldn't be too difficult. Remove the wires one at a time from the shell, and put back one a time to avoid mix-ups. The part of the pin that's damaged is likely the metal leaf that runs down the center of the pin, it's fairly easy to bend it back into position with a pick, but you need to re-shape it so it has drag/tension on the ECM pins again.

The other alternative is to replace the connector shell and all the pins on the ECM A connector, you'll need a special crimper to install the new pins on the wires.

 

[veloman]

Thanks for your prompt reply heli_nut it's really appreciated, makes me a wee bit more confident with an expert giving advice! Although I have a complete plug and more than enough pins (not all the pin spaces are used on the NT and the unused ones have plastic blanks fitted) I hope I don't have to go that route. I'll do as you suggest and just concentrate on the four pins. From what I could see it will be a tight squeeze putting a tool in from the rear but at least I know now which side the pin tangs are on. I've had another look at the new plug and it seems to me that only the tang nearest the front end of the pin may be used to lock the pin in. There only seems to be one tab on the plug body. Perhaps the extra tang on the plug is for another application?
I'll let you know how I get on when the release tools arrive.

 

[mikesim]

The tool is usually inserted from the front. The fingers of the tool compress the metal tangs on the pin allowing it to be removed by pulling the wire and pin toward the back of the connector.

Mike

 

[veloman]

Thanks for the input Mike but I think the pins fitted to the NT ECU plug are of a different type. The "flexible" tang which I'm assuming has to be moved by the tool is part of the body of the plug. The projection on the pin that the plastic tang of the body engages with is "solid" and is part of the main body of the pin if that all makes sense. A tool going in from the wire side would hopefully lift the plastic tang clear of the pin projection.

 

[veloman]

Although thinking about it, going in from the front would certainly be easier but would mean removing the front cap of the plug. Possibly then it would be possible to insert a two pronged slim tool so that the prongs passed either side of the pin projection and lifted the plastic tang clear that way. I really don't know but have some pin removal tools coming so I should be able to see if any of the double pronged tools do the job or if one of the single prong ones works from the wire side.

 

[mikesim]

In looking at your pics again, I think I was mistaken in my advice. It sounds like rc heli nut has some experience with this particular connector, so I would follow his lead.

Mike

 

[veloman]

With the benefit of having both pins and plug body to hand I agree Mike. My only concern at the moment is that in the brief look I had at the wire end of the plug after moving the top cap and seal out there did not seem much (or any) room between the top of the pin that secures the wire insulation and the sides of the square hole for each pin. When the ordered pin removal tools come I'll have a try and see if I can get one down sufficiently to release the tab.