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PAIR and Flapper mod, with bonus snorkel mod for VFR

The Honda VFR is a beautiful machine, but its full potential has sadly been restricted to comply with different laws and regulations. There are fortunately some easy steps you can take to remove these limitations and get the full potential of the 800cc V4 engine.

All the mods are easy to do, and are fully reversible in case you want to restore everything to its original state. Please note that you are doing this at your own risk! Many VFR riders have however done these mods without any complications. The description and images are compatible with the 6th generation VFR, them being from 2002 to present date.

First things first. You will need to find the fuel tank. Ready? Okay, now locate the two screws on the front end of the tank and unscrew them.


Now lift the tank up slowly and make sure that the fuel lines or anything else is not stuck.

Fueltank open

Make sure to put something sturdy between the bike and tank to hold it up properly. This is of course much easier if the tank is almost empty, so take a long drive to empty the tank beforehand if you want!

PAIR valve

We’ll start out with a quote describing exactly what the PAIR valve does. If you know where this was taken from, please contact me and I will of course link there.

What is happening is that when the bike is running, the pair is opening to blast fresh air into the exhaust system. This was done to clean up the bikes emissions. This systems worked fine on all models. Even carb models have this system fitted. When the VFR went to the first fuel injected model the PAIR valve was still used again to clean up emissions without any problems. Then the VTEC model came along and it all went wrong. The reason for this is that the VTEC model had an O2 sensor fitted in the exhaust. What happens is that the PAIR valve is working pretty much from idle speed blasting fresh air into the exhaust system. The fresh air entering the exhaust is picked up by the O2 sensor which then thinks the bike is running lean (around 19:1) so sends a signal to the ECU to richen up the fuel mixture. The ECU is now pouring as much fuel into the engine as it can because the O2 sensor thinks its still running lean. The real fuel/air ratio being poured into the bike is now around 11:1 making the bike hard to ride and resulting in the snatchy throttle response we have all been talking about.

So what we want to do is to disable the PAIR valve altogether and the easiest way to do exactly this is to remove the cable controlling it! If you look on the right side of the bike under the very tank you just lifted, you will see cables and a connector like this.

PAIR valve connector

Now just unplug those connectors and use some electrical tape to make sure that no moisture gets into the open ends.

PAIR valve disconnected

Yes, that’s it! You have now successfully disable the PAIR valve from screwing with your O2 sensors. But why stop there…

Flapper valve

The air intake box is located directly under the fuel tank and you probably noticed the strange little valve on the top right when you lifted the fuel tank for the first time. Its sole purpose is to strange your VFR! That’s right, it limits the airflow at certain RPM’s to comply with regulations regarding emissions and sound. This is also know as the infamous flat spot around 5000 RPM.

It is however very easy to disable it. Just pull out the vacuum tube coming out of it and plug it with a plastic plug or similar. Do the same with the valve itself to protect against dirt finding its way in.

Flapper valve

Make sure to secure the tube with some tape to keep it from slipping out while riding.

Snorkel mod

Yes, you read that correctly. You beloved VFR has a snorkel and it has a hard time breathing through it. Just imagine going out running and only breathing through a straw in your mouth. Not a pretty sight.

The snorkel on your VFR is located on the front of the air intake box and it is made of soft plastic, so it is easy to just pull it out without even opening the air box!

Snorkel intake

Now your VFR finally has the ability to breathe properly, and it will behave much better at high RPM! Just be sure to save it if you want to be able to restore everything to its original state.

The snorkel

You will probably need to open the air intake box if you want to restore it.


I really don’t want to write anything here, but instead let you find out for yourself! I am sure that you will be amazed by what your VFR can do now. If this was not for you however, simply restore all mods, which should be very easy if you followed the instructions above.

Okay, if you really want to know the results, here goes. It’s a completely new bike! Gone are the hesitations on low RPMs and the flat spot around 5000 is gone, and the engine feels much more responsive at high RPMs! In addition to all this, it runs much smoother overall and has a more distinct and “meaty” sound to it. I have the Devil Magnum Carbon slip-on, which helps.

Leave a Reply


  1. Perfect, finally a description of what I actually want to do! As well as this, is it a good idea to get some o2 eliminators fitted?

  2. Can you please add something about the snorkel mod regarding riding in heavy rain.

    The purpose of the snorkel is to ensure water doesn’t get sucked into the airbox.

    Other than that, nice writeup + pics :)

    • Thanks!

      I haven’t tried it out in heavy rain, but if you do, have a look in the airbox to see whether water has entered it or not. I’m guessing that it would take a lot of rain before something would happen.

  3. Most of the articles I read refer to blocking the pair valve. It seems like disconnecting the pair valve solenoid does the same thing but much more elegantly. Why is blocking the valve so popular?

  4. Mmmm, interesting… it “inhales” better but I wonder if the stock exhaust will restrict the motor “exhaling” as well and thus limit the success of this mod… I’m having major surging issues lately and very rough running at low RPM… and snatchy throttle response… even in VTEC regimes… one thing caught my attention regarding this article and that is that everywhere I’ve read about this matter, the VTEC is stated as “famous” for runnning too lean… especially in constant throttle conditions (stoichometric mode), which is the only time the O2 sensors really come into play… I reckon I’ll give it a go as I’m desperate to have my butter-smooth ride back…

  5. I have a 2002 VFR. I bought it in September, 2010. The original owner bought it new in ’02, put 100 miles on it and parked it. It ran very poorly under 6000 RPM, was fouling plugs, surging, and cutting out at idle. I took the bike into a Honda shop and the problem was determined to be low output from the alternator. It was replaced and the bike absolutely rocks! I runs smoothly at all RPMs and floats the front wheel in first and second gear with no problem. By the way, I did the pair valve and flapper mods after the bike was repaired and it runs even better now.

  6. I worked at a Honda dealership in the early 90’s… and I owned a 1993 VFR750, just bought another recently… dyno runs with the snorkel removed showed a *loss* of 1HP at most RPM’s, and a *gain* of less than 1 HP at RPM’s above 9000. Torque figures were identical (within margin of error of measurements).

    This was consistent across 1990-1994 bikes, not just the VFR but many Hondas. I haven’t tested any newer bikes, but I wouldn;t imagine the results are any different.

    Removing the snorkel really adds no power but it makes the bike’s intake SOUND much louder… every customer we had swore their bike was much more powerful and they could really feel a difference after the snorkel was removed… although the horsepower and torque were essentially unchanged. Just my two cent’s worth.

  7. Easy to follow instructions and technical explanation. I just realised how much effort I was putting into riding around the poor fuelling. Many thanks Johnny.

  8. I worked my way through college as a part-time mechanic and helper in the largest dealership in the Southeastern US (one of the largest in the world). We performed all these mods on various Honda bikes, and ran dyno tests before & after each one… no seats of the pants golleee gee whiz this rocks #@$! but actual output power measurements.

    On most bikes, the PAIR valve mod makes no difference (less than 1HP + at top – at bottom, for a net gain of “zero”). But the PAIR valve on 5th & 6th gen VFR’s were not well engineered, the PAIR valve mod does make a difference on the 5th & 6th gens – not on the 3rd or 4th (except shaving a little under two pounds weight).

    The flapper valve does make a significant difference – barely measurable on some years but significant on others.

    The snorkel mod just makes the bike have more intake noise so it “feels” like more power – dyno results show less than -1 HP at low RPM and less than +1 HP at high RPM. Those numbers are actually within the margin of measurement error even for back-to-back computer corrected dyno runs of the same bike on the same day. Removing the snorkel does make one heck of a lot more intake noise at high PRM’s, the extra racket may translate to the bike “feeling” more powerful to some… literally makes no measurable difference in HP or torque. On low-end and midrange RPM, some years suffered reduced or mushy response at WOT when the snorkel was removed; some units also suffered longer 60-80 top gear roll-on times with the snorkel removed. However, everyone I ever spoke swore up and down that removing the snorkel made their bike WAY more powerful. People believe what they wanna believe, numbers don’t really matter…

  9. 2006 VFR800
    I did both mods, but it actually made it run worse.
    Tested one or the other, the bike ran a little better with just the PAIR valve connector disconnected (but Flapper connected)

    Having PAIR enabled and Flapper disabled made no difference.


    • I have my PAIR valve plugged. Use a marble. Cleans up a bit just off idle and low speed constant throttle.
      Blocked the tube leading to the flapper valve. Does not run as good. Seems to labor/run rough up to about 4500rpm. Can feel it thru the foot pegs. There might be an improvement at slightly higher revs but not worth it. Put the flapper back to standard. Tried this twice now and same outcome.

    • Same here mate, disconnected my pair valve connector and bike runs a lot smoother less snatchy, tried the flapper and exhaust started popping, seems better just with the disconnection. I’ve read elsewhere that disconnecting the pair actually leaves it on though which would mean more air into the exhaust system making the 02 sensor think the bikes running lean?? That’s probably why a lot of VFR owners remove the whole pair system,confusing isn’t it!!! Dont no what to believe. all i no is my bike runs better now, hope its not doing any damage, still looking around for info,good luck with yours,Mines an 03 vtec.3800miles

  10. Massive improvement to my 09 vtec. Before it had all the problems snatchy throttle flat spots and surging. I now have a different bike it seems revs smoother and not flat spots. Awesome mod.

  11. Cableguy – Dyno runs match your experience. Dyno shows “little to no” difference with the PAIR valve mod — a small enough difference that it’s within the magin of error in dyno measurement capability — but it does shave some unneeded weight. The only numbers I believe are those on they dyno or actual track/strip times. I’ve met very few people who didn’t think that any mod they performed was an awesome increase in power, speed, etc… even when dyno and track numbers said otherwise. IMO most motorcycle “power modifications” just make the bike louder and/or vibrate more so it feels more powerful. I put K&N filters & Slick 50 & other snake oil in that category.

  12. Hi, just done the pair mod to my 2004 VFR VTEC- it was afwul for me at low revs, junctions etc – it’s made a huge difference and feels like a new bike!!

    One thing bothers me- has anyone had any negative issues as a result, such as cat failure, emmisions problems etc? Any feedback would be great. Thanks.

  13. Alright, done the PAIR & the Flapper valve. Have not ridden it yet, so I’ll let you know. I’ll leave the Snorkel for the mo. When I 1st got my bike in June, I thought that it was just a matter of me adjusting to my new ride, trying to find the right amount of throttle to take off or slow cornering (not enough or to much), could not find the sweet spot.So here’s hoping.
    The bloody flapper valve is really annoying & IMO makes the bike sound like a POS & distracts from what is a sweet sounding V4.
    Has anybody else that’s done the PAIR mod, noticed any improvement in fuel consumption? The one thing that has really surprised me is the piss poor fuel consumption compared to my last bike (in line 4).

  14. Well took her for a blat today, 1st ride since I did the mods, blew a tiny amount of white smoke at start up. But I suspect this was water vapor as its 31C & 60% humidity here & it dissipated almost immediately.
    Bike went well, seemed a lot more controllable slow cornering & getting away at the lights, which is what I wanted, no more playing silly buggers with the clutch.Wrung its neck a few times well past 7000rpm in low gear & she just lifted her skirts & went for it. Nothing negative to report about at all. Thanks for “How to”.

  15. Hey great article, i myself own a 99 yellow vfr800 and being completely honest it is the mutts nutts……… Over the years i have owned blades, big zeds(zzr11), ninjas etc etc etc, and by far this vfr kicks the shoite outta everything else. Not speedwise, as the zz i had was a quarter miler and was cranked up as far as possible (crank, cams, big bore, advanced timing system huge carbs, power commander and sometimes nitrous). No wonder i smashed it lol, but this vfr, sheer comfort, the ride position, the lovely purrrrr of the v4, and the way she handles…… 2nd to none. I just completed this PAIR valve and snorkel mod this afternoon and took her a blast up the roady….. OH MY GOD!!!! I about soiled myself with joy, the note that comes oot the remus c/f gp hi rise can now deafens me. Which is a good thing!!!! I couldnt find the wires under the tank to pull apart but i dont really care that much, as the performance really has gone up one or two ponies. But why stop there?? Thinking of installing a pcv/pc3 soon, but living in scotland, its kinda hard to get power down as the ass slithers around a fair bit under sudden acceleration, again, adds to the fun factor. Ive never came across such a user friendly bike before, and this one i intend to keep. 32k miles on her and pulls like a train, no knocks, rattles or leaks, and starts 1st turn o the starter. No probz with the rectifier as ive introduced it to its own little cooling fan and hooked it up to the main cooling fan, so wen hot, in it kicks, and keeps the rec nice and cool, instead of frying its brains in. My mate also has a vfr 800….. His is a 5th gen also but an 01, and hes just spent 00s making his bike more up to scratch, same exhaust as me, single seat, amongst a few other things, im not gunna tell him about this mod, not yet anyway….. Imagine his face when wer out on a run and his newer vfr takes a right hiding off the same bike…….. and the best bit……. It was FREE!!!! Cheers guys, am off out fer a blast on mi noo viffer! Mikey

    • Ultrasonic is correct and sounds more like a real mechanic minded person like me. Guess work is for dummies be a real man and study!

    • You might want to specify what Year VFR service manual you are referencing. The operation of the valve may be different from 5th gen VFRs to 6th gen VFRs. My ’08 service manual states that the pair control valve is normally closed. The ecm sends current to the solenoid which opens the valve. So disconnecting the connector on a 2002 – 2009 model should effectively shut off the pairs system.

  16. I ran my VFR800 for 8000km with the PAIR valve blocked off. It improved the just-off closed throttle and low speed fueling. It did not cure it, just made it much improved.

    I then installed a Dobeck TFI fuel controller which required the O2 sensors to be bypassed. The bike ran really good, plenty of power, better just-off closed throttle and low speed fueling. Only downside is when starting the bike, it would not fast idle unless really cold. I also had to bump the hot idle speed up a bit.

    Even before fitting the Dobeck TFI fuel controller, i was getting a knocking noise coming from the engine area. Only noticed it at idle and it only did it infrequently. My Honda workshop manager heard the noise and was at a loss as to what it could be. He knows the mods i have done to my bike and suggested it could be the PAIR system. The PAIR hoses from the reed valves are still subject to a vacuum and the noise could be pulsing within the ‘open’ part of the PAIR system.

    I re-enabled the PAIR system (only mods now being the Dobeck TFI fuel controller and O2 bypass). On starting the bike (from cold) the fast idle worked. The exhaust sounded different at idle. Just-off closed throttle and low speed fueling was now spot on. Overall, the bike went better, sounded different, fast idles when cold and i could drop the hot idle back. Bike will now hold 3000rpm easily and pulls out of slow corners and roundabouts from just over 2000rpm, with no snatching. I can now ride the bike slowly.

    The PAIR valve simply stops dumping air into the exhaust, messing with the O2 sensors. The PAIR valve also seems to be adding air to the combustion process (increased idle speed).

    Maybe, just bypassing the O2 sensor, with no other mods will achieve part of what benefits i have obtained. One day, if i can be bothered, i will turn off the Dobeck TFI fuel controller and see what eventuates.

  17. With all due respect, this whole article is full of nonsense and heresay.

    For starters: the PAIR valve is NOT adding fresh air into the exhaust for most of the time as someone already pointed out who actually measured when the valve is activated or not. And I canconfirm that: the valve only lets air into the exhaust during idle and when closing the throttle at driving speed. So this mod brings you nothing.

    The mod for the flapper valve is even more hilarious. You say that the flapper “strangles” your eninge so you suggest to remove the vacuum hose to disable the flapper. And I read this on numerous other forums: Everyone advises to pull the hose off and plug it. Apparently noone knows how this flapper valve works. This valve is normally CLOSED and opens by applying a vacuum. So by disconnecting the hose, the flapped valve will stay CLOSED AT ALL TIMES!!!!

    I suspect that the flapper is opened when the VTEC kicks in, which explains the change of sound of the engine (actually the sound of the air intake). I did not rev the engine up above “VTEC speed” but I could see that the flapper stayed closed on low rev speeds.

    • Actually, it is you that does not know how the flapper valve works. If you read the 6th gen service manual, it clearly states that the flapper valve is held open by the spring. Its natural state is wide open. The ecm sends power to the solenoid to open the control valve which allows the vacuum to act on the diaphram which “closes” the flapper. This may or may not be different for other generation VFRs, but this article was written for the 6th gen VFR and the information on these procedures is correct. The benefit of these alterations is another story and obviously much more subjective.

      • To be honest, I do not know which generation my VFR is, I only know it’s a 2005 model without ABS. And when I look into the opening in the airbox, I see that the flapper valve is held closed by the spring, closing the extra air intake. When vacuum is applied, the flapper valve opens.

    • I just took my airbox apart. forget what the manual says, you can clearly see the valve is open under normal conditions. it’s pretty obvious. vacuum being applied would close it. seriously. apply vacuum to it. see what happens.

  18. Hi. As I’m doing some shuttling to my work downtown Oslo, I was really considering to change my VFR 800 2009 model due to the “uneasy” riding at low speed, traffic lights starting etc. I did the Flapper Valve mod some weeks ago without much improvement. A couple of days ago I did the PAIR Valve mod. Many thanks for giving me a “new” bike! I’ll keep it…

  19. I just did the pair valve and I can say the improvement is huge.
    No more stuttering below 4000rpm. I can now ride my bike without issues at 2000rpm without jerking like a tractor.
    Maybe I’ll also do the other 2 mods in the future.

    Thanks for the great guide!

    • Well, I’ve just done it on my 02 model and I’m very pleased with intial test ride. Hopefully get a proper ride at the weekend but it’s a thumbs up from me!

  20. Just bought a 05 with 22 thousand km, it was snatching/noisy and just plain horrible at any small throttle opening or cruise. Both mods have made it smooooooth . Thanks a bunch

  21. Hey John,i bought a real aweet 2006 VFR 800 wheni traded my 1999 Yamaha Rotle Star Venture ,loing story ,but I broke my left ankle really bad and just coulsn’t deal with the weight of the big bagger anymore .
    So I found the VFR at my favroite bike shop all pearl withe [My favroite color BTW] with only 4,00 miles for $5,500.00 I had to have it . on it and loved it rightaway .I did noitce the falt spot and choppy throttle responce.I did the mods you posted,pair,flapper and snorkel and what diffrence it makes .some say here tha this only gains you 1 H.P. ,but before doing this I had to MAKE the bike wheel stand.I just took it down thr road and rolled on in 1st and speed shifted into 2ed and up she came .
    Now she’s smoother seems to make more power and sounds better.As soon as I can find a set of stock 2006 can’s I’m gonna do the mod on the new set and keep my set original .Now I really love this bike .Thanks for posting these simple mods ,they really make a diffrent bike .Lou

  22. I test rode a new VFR800 (only 64kms on the clock) and it was “butter smooth” as someone else has described it. Just an awesome feel to it. It was THAT ride that convinced me to put up the cash on a new VFR. But I didn’t buy from that dealer as their “sales manner” was atrocious (as it was at several other dealers – but that’s a different story).

    I’ve been really annoyed with my new bike’s “snatchiness”, at low speeds in particular, compounded by a “grabby” clutch operation. The service manager at the dealer I did buy from had every excuse under the sun for the “snatchiness” – “it’s within spec”, “it’s only new yet”, “it’s the way you’re using the throttle”, and so on.

    I did adjust the throttle cables for excessive travel, and that helped me cope better with the problem. But I just took my 2 month old 6th Gen out for a test ride after doing the PAIR and Flapper valves mods as suggested. Now it’s much, much better at low speed and in suburban riding. Worthwhile doing for sure – I’m now much happier with my VFR. Have yet to check it out on longer and higher speed (cruising) rides, but I’m optimistic.

    I wonder what had been done to that demo bike to make it so nice to ride? I’m looking for a mechanic I can trust to service my bike in future.

    Thanks for your help John.

  23. I have a Street Fighter and was wanting to extend the snorkel so that it comes out towards the front of the bike for direct air flow and for looks. You think this will be as good or better than removing the snorkel tube?

  24. Took delivery of my new (to me) 2009 VFR800 and after several miles, the only problem was the ‘snatch’-iness of the throttle at low speeds. This was particularly noticeable when setting up for a 90deg turn at an intersection. Approaching the intersection on the brakes, shift down, off brakes, start turn and slowly roll on the throttle, and I’d have to use the clutch to stop the bike jerking. And when the throttle came on, it was quite harsh.

    Did the three mods (flapper, PAIRS and snorkel); no noticeable change in power but the throttle at low speeds was so much more controllable. The bike has become much easier to ride at slow speeds.

    Haven’t really noticed any change to the sound. But that could just be my ears :-).

    All in the mods took me at 15 mins. Thank you for this.

  25. You’re not taking that turn in first gear I hope. My advice would be: shift down one gear less and apply more power once you’re halfway the turn. Kicks you out of the turn smooth and powerful. Much more fun than trying to take that turn too careful… ;-)

  26. I decided to try the three modifications on my 2003 VFR. My VFR is all stock with the exception of a K & N air filter from the previous owner. For what it is worth, I did notice a much smoother delivery of power and the flat spots and low-rpm surging were eliminated. It also has more audible grunt during idle and acceleration. The “V-Tec” transition at 6200 RPM is not so abrupt either. Very easy to rev it and let it go. Turned out to be a winner for me. Everything is easy to reverse so I would say give it a shot. It may not have increased the power output, but making the delivery of power smoother was what I was after. It did the trick. Thanks for the information everyone.

  27. I went one better…

    I took my VTEC engine out and put a ’99 Fix lump in. Swapped starter and alternator over, used the VTEC throttle bodies all balanced up square and reshimmed the valves. I modified the cam covers and with PAIR still running, the flapper in place and all standard except for the permanent 4 valve system it runs sweetly and lifts the front under power in first.

    Bit drastic but hey ho. BIKe UK magazine said at the time they should have left the earlier engine in and I just wanted to see if they were right.

    They were. Best of all worlds, awesome lights, ABS and no VTE lurch.

  28. I followed the instructions and also fitted a pair of O2 eliminators at the same time and for the first time since buying the bike back in March this year, I’m truely enjoying it. The hesitancy and snatchiness has all gone. It’s just pure smooth drive right up to when the vtech kicks in ;) . Thanks for the guide Johnny :) .

  29. Well, I have to say this MOD is amazing. I was having the same problems as many people, the bike would snatch all the time.
    (I have a 2002 VFR VTEC with 32K on the clock)

    In fact, I was thinking of selling the bike up until today!!!
    Most annoying thing was when the throttle was closed and then opened up again, which made it feel terrible out of corners. Gear changes were very snatchy, no matter how gentle I rolled the throttle on and how slow I released the clutch. I also had a hesitation at 6000, just before the VTEC kicked in at 7000. When the VTEC did kick in the bike would lurch forward, which was awful especially when carrying a pillion.

    I found this MOD and decided to give it a go as a last resort, I am so glad I tried it. My bike is totally different!!!! In corners it is so smooth, gear changes are smooth and it now accelerates all the way up to the VTEC with no hesitation. When the VTEC does kick in, the transition from 2 to 4 valves is seamless!!!! Amazing!!

    Dont bother with this if you are looking for power gain, there is none. If you are after a smoother ride then this is a simple MOD which costs 10min of your time and £0.

    Thank you for posting such a detailed MOD that works wonders!!

  30. Did mods minus the snorkel removal on my 06 with 5K. Bike has been for sale for 6 weeks due to snatchiness. Just took my ads down. I’m in love again. Thanks for the great mods & advice. Dallas.

  31. So I tried the first mod (unplugging the connectors) on my 07 VFR800 non abs. The bike felt the same below 3k rpms, rough with surging. It made a tiny improvement running it at 2k rpms in first to second in parking lot situation. I was wondering why everybody else in all forums related to the VFR recommend plugging the airbox & the housing of the pair valves. The block plates seem for those that want to remove everything.

    This is my first bike and it only has 3700 miles so it is relatively new. To be honest I haven’t riding her much because I keep on stalling it most of the time getting out of 1st. It handles horribly at low speeds and that’s where a newbie is more than likely be cruising at. I’m very discouraged and disappointed with my purchase. I’ve been thinking of selling it and getting a Ninja 300. I’m only 5’7 and after doing the triangle flip mod I have both feet on the ground but not completely flat.

    I want to buy a PCV and Helibars but I’m reluctant on whether it will make a significant change to keep her? From what I read on the power commander, it doesn’t completely get rid of the surging or low rpm problem. As far as the Helibars, it doesn’t come close to an upright riding position so that’s where I’m at with her. Any advice will be greatly appreciated.

  32. Sell it, Its a great bike but not for you. Look at a 250 – 500 with a more upright seating position Take a beginner rider course and then an advanced rider course, then as you ride you can advance into a bigger bike that suits your riding style or maybe its just not for you and the entry level bikes if bought used and cared for hold their value pretty well. Ride safe

  33. I’m interested in these mods but would like to know what this does to the stupid annoying fault codes on the fi light as I have just cleared these and don’t want them back again