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AdBlue fun - countdown - Nox sensor - injector

Discussion in 'Alhambra' started by timhowarduk, Dec 27, 2018.

  1. timhowarduk

    timhowarduk Active Member

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    Hi
    Having learned more than I ever wanted to know about the AdBlue system on my 2011 Alhambra I thought I'd start a thread collecting what I've learned over the last 2 years.
    Lot's of people complain with bewilderment when a message flashes up saying "Top Up Adblue", with a range of at least 1500 miles. This is no big deal, you top it up, leave ignition on for 30 seconds, start engine and get on with your life.
    But if the message is "Check Adblue" with a range of around 650 miles with no prior warning this is usually the start of some fun which can turn expensive.
    The first throw of the dice is to top up the AdBlue. 99% of the time, even after doing this the message won't go away and the countdown will continue.
    Ideally at this point you can find someone with VCDS scan software or buy it (£225 delivered) to give you reliable information about what is wrong. It will tell you what the ECU considers the AdBlue level to be. Often it will say "Full". Whatever you do, don't buy a cheap generic scanner and clear all codes, it won't help, and it will prevent the correct software helping you until you have driven another 50 miles.
    The two most common failures seem to be the Nox Sensor failure (located roughly in the middle of the car on top of the exhaust) or the AdBlue Injector (located after the cat on the exhaust).
    The Nox Sensor will usually throw error "Nox Sensor 2 Bank 1 - Implausible value" on a VCDS Autoscan. It is well worth attempting cleaning it before paying £400 for a new part. It's a 22mm spanner for the injector, but to remove the controller you have to take off the heat shield cover which is a few 10mm plastic bolts and finally 2 x 10mm nuts on the controller and one electrical connector.
    You might be able to talk a tyre/exhuast place into loosening the sensor for you on their ramp, it takes them a couple of minutes and it makes it a lot easier when you are under it later on stands on your drive. It's worth disconnecting the controller first to avoid twisting the cable a lot when removing. Once the sensor is off, cleaning it with oven cleaner and heating it gently with a gas torch until cherry red can coax it back into life and I got another 1100 miles without any issues after doing that.
    While under the car, it's worth checking the AdBlue injector too as it's very easy to remove. It's a single hex head bolt on a clamp holding it on. If crystalised, it all needs cleaning off. Then you can run the "SCR Metering Test" in VCDS with just ignition on (NOT engine running) and check you see it squirt (from a safe distance).
    Having checked injector is squirting and sensor is clean, you can either drive 50 miles and wait for the car to notice it's happy again, or run the "Check SCR efficiency test" in VCDS. Hopefully all is happy, the warning goes away and life continues.
    If you get down to zero miles, running "[Reset SCR Lock]" in VCDS is supposed to give you another 50 miles. I've not needed to try this myself yet.

    My current situation is that having done all of the above, the message remains, the countdown continues. The fault codes still relate to the Nox Sensor so I'm about to fit a new one as cleaning it no longer works. I'll report back once this is solved.

    Another common problem is the heater in the AdBlue tank failing. AdBlue freezes at -10 degrees. This usually just puts the engine management light on and doesn't put the car into "countdown to doom" mode. In the UK, this problem can be ignored for a long time! If fact there is a hack available to bypass the heater completely instead of replacing it. However during winter in some regions the heater needs to work and there is a kit available to change it (about £400) and youtube videos showing how to do it. It isn't a hard job, but rear bumper needs to come off.
    Frankly, this whole system is a pain, and it has caused me sufficient stress to be considering carefully whether I want another Euro 5/6 diesel with AdBlue. As a caravan owner with 4 kids options are rather limited though!
    Hope the above helps someone, and I'll confirm the fix for the latest issue when the part arrived.
     
    #1 timhowarduk, Dec 27, 2018
    Last edited: Jan 2, 2019
  2. Very helpful just to add into this I think this issue is common across many makes. I have a Transit Van and it suffers lots with error messages, they go and then come back again later and the guy who delivered the van did say he has lots of issues with AdBlue
     
  3. timhowarduk

    timhowarduk Active Member

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    So, as promised, the happy ending.
    I replaced the Nox Sensor, took car for a drive to get it up to temperature (over 80 degrees Oil Temp), than used VCDS to run the SCR Efficiency Test which passed, and the countdown stopped. The basic golden rule is never clear emission related fault codes until they make sense.
     
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  4. Katie Molina

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  5. timhowarduk

    timhowarduk Active Member

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    I recognise the frustration. From what you have said, I'd agree this is the most likely reason for the fault. To be sure I would suggest finding someone near you with VCDS diagnostic software (post whereabouts you are based, many will do a full scan free or for under £20). Alternative there is also a unit called Autophix V007 that gives you specific VW codes, make sure you get the VW/Seat version. With the full code and message you can then be almost certain it's the sensor.

    A new sensor is unfortunately £350+ without fitting. I got a reconditioned one with a 12 month guarantee for £125 off ebay. Seller name was www_teilemania_de . ( https://www.ebay.co.uk/itm/Audi-VW-...7807F-Oxygen-5WK96689-12-Months-/292831487295 )

    I too the under car cover off, drove to a local friendly garage and they loosened the sensor for me on their ramp for free. Then I got the car on stands at home and it was fairly easy to change them over.
    If you are not doing it DIY then you may be able to convince an exhaust place to change it over for you. All the best with it.
     

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