emissions failure

[MightySlay3r]

hi guys, i do hope you can help me.
just before xmas my son & I had to changed my cat & flexi hose.. they where shot...
citroen c4 grand picasso 2016 hdiblue 1.6
now, we removed the 2 sensors in the side of the cat that went to 1 plug, removed the adblue injector & removed & replaced brand new cat & flexi hose. replaced the 2 sensors & adblue injector.
fired her up & purred like a kitten. we let her run for 10 mins or so to get somewhere near temp then went for a spin down the motorway at 70 mph.. i can go any faster has i have a dreaded black box fitted... it knocked £400 off of my premium so im fine with that has i dont speed anyway...
anyway.. after about 15 miles we exited the motorway on a roundabout & headed home... about 10 miles from home i got a warning... [engine fault]. & brought up on the satnav different close proximity garages for repair... so im bricking it wondering what was wrong... a couple more miles & got a warning [emissions failure.. vehicle will not start in 700 miles] ... now im more than bricking it... 10 miles from home.. is it going to cut out? should i pull off of the motorway & find an alternative slower route etc....
decided to stay on the motorway at 60 mph... got home.. went to friends garage... he checked it over & said everything seemed fine... he put is diag machine on to it using the obdII port.. ran a scan...
came up with ghosts, mini faults that had corrected themselves & gone void & urea faults (adblue)
now, it told him what road i was on, what speed i was doing, everything.. apart from what was actually wrong with the adblue system....or engine fault...
he reset all the error codes & told me to pop back where i'd come from & give it another blast on the motorway.
it did the self & same thing in almost the same place on the way back.... went straight back to him. he said it maybe the cat sensor that need replacing.. £86 later from autodoc, he fitted them.. reset the codes.. went on same journey.. didnt even get 2 miles on the outbound journey & all the bells & whistles started up again...
i have just ordered some WYNNS Ad-Protect Ad-Blue Crystallisation Preventer 125ml which i will be adding to my adblue tank tomorrow has i've been told the sensor in the tank could have crystallization on it... from a cat & flexi hose change? it was running like a dream before we changed those...
if anyone has come across this after changing their cat.. could you please comment if you also had this problem... i have been cracking my skull over it for 2 months & now the reading says i only have 300 miles left.. and yes the adblue tank is almost full.. we topped it up when the msg first came on & i've driven about 400 miles trying to get the damn thing back to how it was... no luck
thanks in advance guys

[RichardW]

It might be coincidence, you might have knackered the ad blue injector. You need to watch the live data from the denox system whilst it warms up and starts operating to see where the fault lies. You should get:
Waiting (or words to that effect) - pressure should 4 bar
Pressurising - pressure ries to 6 bar
Injecting - pressure drops to 5.5 bar, NOx should start to fall

Once you can see where it falls over you should be able to figure out which bit is broken.

[MightySlay3r]

thank you Richard, i'll keep an eye on that next time my friend attaches the diag machine...

[MightySlay3r]

what i dont get is.. we put the adblue injector out of the way.. so as not to knock or damage it.. all we did was undue the clamp, pull it out & tie wrap it up & away from the cat ...
anyway.. i put the already mentioned additive in the adblue tank... had to take some adblue out using my wifes turkey baister (need to buy her a new 1)
took it for a 70 mph blast down the motorway (m1 from leeds to junction 38...) going up the off ramp to the roundabout.. check engine light came back on with engine fault.. is that because the oil & engine temp had got to operating temp?
still drives perfectly.. just excessive fuel usage...
still need my mechanic to use the diag machine to watch the pressure of the adblue though...
my friend also said it could be the nox sensor.. but we didnt go anywhere near that...
everything is trial & error.. but its getting expensive & only 250 miles left before non start... getting desperate...

[GiveMeABreak]

See my post here on the system, as there may be pressure in the accumulator but that doesn't confirm the pump is working, as the accumulator is designed to hold pressure until the Adblue is dispensed and then as Richard says, when it drops to about 5 Bar it is supposed to trigger the pump to repressurise the accumulator.

viewtopic.php?p=830046#p830046

[RichardW]

A decent scan tool will allow you to reset the de-nox system and get another 700 miles....and another 700 miles...etc!

[MightySlay3r]

thanks Marc.. i'll pass this on to my friend with the autel scan machine.. should at least rule out some of the issues.. just hoping its not a new tank needed... dont have the readies to cover it
thanks again Richard, i think my friend mentioned something about reseting it to give me the 700 miles back... but wonder if it will pass an MOT if the emissions arnt right...

[RichardW]

They don't test for NOx, but it will fail if the engine light is on.

[MightySlay3r]

ok, my mechanic & I are scratching our heads....
the autel diag system found the "pre cat" nox sensor wasnt giving any readings... but the after dpf nox sensor was...
we have searched high & low on the web & car for this pre cat nox sensor... anyone know where it is at all?
thanks in advance

[RichardW]

Doesn't have one, the upstream figure is fictious.

[GiveMeABreak]

It's generally only the Euro 6.2 systems that have an upstream and downstream NOx sensor. Prior to this it only has the one.

On my Aircross I have 2 shown at (6), but you won't hve the one I have put a red cross through on your vehicle.

[MightySlay3r]

ok thanks guys... i think my man is leaning towards the nox system... its the only thing thats throwing up a fault... but doesnt say what the fault actually is lol

[RichardW]

As I said above, you need to watch the live data as it warms up to see where it falls over which will then point to where the fault might be....