The sensor down stream of the SCR can tell the difference. After the process of the add blue being added and the catalytic reaction the sensor expects to “sniff” a specific content of gases if these gases fall outside of the correct window of operation the system tends to log an efficiency fault code something like P20EE.

The exhaust sensor will pick up a difference in what it expects to see out the end. Then trip out when its wrong. Great advice on it resetting after 250miles very interesting.

It’s far more likely there’s an emissions sensor. You should use demineralised water as limescale will build up on the jet. As it is the adblue crystallises on the jet

The match of 250 miles to detect and clear the fault indicate it's probably a sensor further down the injection system rather than in the tank itself. The fluid in the pipe between the tank and injectors needs to be used before the content in the tank reaches that sensor.

i think it registeres that the sensor on the end of the exhaust realised that there wasnt any nitrous oxide being broken down and there was an increase so that emc flagged this up as no add blue,

When Add Blue is added, the temperature in the exhaust system is raised. It is at process that depends of a number of factors, like the outdoor temperature, driving speed etc. The system that monitors the exhaust, measures the temperature, and will calculate this rise in temperature over a period. If the temperature is not matching the expected rise, something is wrong with the Add Blue. With information from other sensors in the system, the monitoring system can determine what is wrong, and this will give you a dashboard indication. The reason it takes 250 miles for the system to figure out what is wrong, is that other factors that affect the exhaust temperature, must be ruled out first, and that takes time.

Uretha! Haha

I'd be interested to see what percentage of water you could run before it figures it out

A problem we had with adblue systems on buses came from the tanks on the buses being filled from a can, rather than the dispensing tank and pump. This was allowing crystalised adblue from the can to block the teabag filter and the dosing pump, putting the bus into limp mode.

You should at least use distilled/deionised/reverse osmosis water, as the minerals in tap water will poison the catalyst. There is also a NoX sensor before after the SCR catalyst and looks for a 60% or better reduction in NoX. During a shortage of adblue or apocalypse it could keep you mobile though.

I worked in a main dealership and filling up with everything but Adblue was a common theme! I’ve drained water, diesel , oil , washer fluid, and antifreeze out of Adblue tanks over the years. If I took a sample and the tester showed NOT Adblue , then it was automatic pump ,drain and flush quote. The pump units are very expensive and water corrodes them fast!

Watch out for those clear plastic cans of add blue on the forecourts. Always take it from a tank. Its UV sensitive and the additive breaks down. I've had problems with an Iveco truck, it was the Iveco dealer engineer who came out on a breakdown who diagnosed the issue.

Thanks for testing this out I always wondered what would happen 😅

You can deactivate the EGR and Add Blue system. If you also unblock the emmision filters cat & dpf, your engine becomes more reliable afterwards and you gain much less fuel consumption.

ADBLUE is part of the Selective Catalytic Reduction system that removes NOx from the exhaust. there are two sensors (post & pre NOx) if you use water instead of ADBLUE then these sensors will register no change in NOx level emission and the engine ECU will know and so register a fault in the SRC system

Limewater is the common name for a dilute aqueous solution of calcium hydroxide. Calcium hydroxide, Ca(OH)2, is sparsely soluble at room temperature in water (1.5 g/L at 25 °C). "Pure" (i.e. less than or fully saturated) limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. Lime and water = Ad blue replacement

Interesting. The 250 mile gap looks like an arbitrary lag programmed into the system by the manufacturer. The major none-water component is urea by the way. It is injected into the exhaust to break down the NOX molecules. Since water would not do this, the NOX sensors would pick this up fairly quickly. Urea is a major component in your pee. Maybe you should try an experiment with say a 50:50 water to pee mix instead😂.

This is why I hate modern cars with stupid computers. Nothing beats good ol cars that have no fancy computers, sensors and shit.

water won't create the ammonia required in the scr cat to break down the NOx gases so the NOx sensor after the SCR Cat detects higher than specified NOx levels and registers the fault it doesn't create the fault straight away as it gives a period of time to try rectify itself by increasing the dosage though on the plus side you may have reduced some crystal build up on the injector and orifice with the water

You should have used distilled water and only in the summer. Adblue freezes at -11 degrees centigrade.

I imagine it works on conductivity between two probes. A 66% water/33% urea mix will have a specific conductivity that is different to just water and it just measures this continuously. My guess anyway.

Interesting as I recently had a problem with the adblue cystalising. I think the adblue injector stuck open and car acted like the turbo had gone. White smoke and ammonia smell. Changed injector easy job cars running fine now.

The system takes no notice of what you put in the tank - it works by measuring the exhaust gases, after the adblue injection in the exhaust, and it expects a specific range of emmisions/Nox - if you've got adblue in the Nox results will be in range - anything else, water, tea, coffee and the figures will be wrong and upshoots your fault message

Thanks for sharing your experience. I have wondered about that. I'm sure a lot of people have and are trying to avoid this expensive additive. Following from Sydney Australia Cheers

interesting to have achieved 250 miles, what would happen if you were to dilute the adblue by say 50% water? would you achieve higher mileage before it registered?

Nice one mate, would have never have thought of just water, could be useful to get out of a pickle if need be 👍

We bought an Audi Q3 in 2014 and it was calling for Adblue top-up every 1500 miles. Was my first experience of it so didn’t question it, but at the time you couldn’t get it from petrol stations, just the dealer’s service department. It was the guy on the counter who ended recognising how much I was buying and said it should be around 3500 miles between top-ups. Queried it with dealer when the car went for a service shortly after and was told they’d look into it. When I picked the car up they said they “couldn’t find any issue”, but low and behold the car didn’t ask for a top up for another 3500 miles and stuck to that periodicity until we sold it…

ad blue has a different density to water, easily checked with a hydrometer, also a different coefficient of expansion, so a full to brim tank of it will leak out if thetank is left out on a v hot day. more of a problem with trucks where the tank can be in the sun. The 250 mile tip is useful thanks

I'd be interested to know if a retest was done using some form of purified water (e.g. distilled) because tap water is full of impurities which could have built up over time in the system. also interested to know how far you can water-down AdBlue before it causes a problem

What if you alter the % of demineralised water from 66% to 70/80/90%?

At 1'40" in, the presenter states AdBlue contains 32% urethra (Urethra is the tube that lets urine leave your bladder and your body) AdBlue is made of a mixture of urea and deionised water.

Greetings from California. Let me tell you, I'm just running into that. I once did it. I added probably 500 ml of distilled water; is the only one that can work, tap water wont make the trick because its minerals and impurities and the sensor will catch it fast; to my wife's X5 35d and it helped to clean some stubborn codes that were making to fail the smog inspections required by law every other year in California in order to register your car. It worked! After doing that, this year I'm having some codes with the Nox sensor in my beloved small beast 2011 335d, so I decided to do the same trick. Well, since last time worked like a charm, this time I probably added way too much water, almost a gallon of distilled water to the brand new DEF liquid from BMW, it went well and it happened the same like happened to you. The Sensor It didn't recognized it at the beginning but after about 100 miles, finally the car told me it had the good DEF. For about 300 miles it ran without any countdown warning, added it when I had only less than 150 miles, since I wanted the water to clear things inside. But I guess it was a bad idea since after those 300 miles of driving without any issue, last week came back the 200-mile warning saying "Bad Nox Exhausted Liquid..." So this time I'm guessing it was too much water in the mix and the sensor caught it, I tried to add more DEF to make the system recognized the real deal is in the tank but it didn't work. So I just finished draining the active and passive tanks, I used a siphon pump, $7 in your local hardware store and it makes the process to be over in less than 10 minutes, and then I added about 1.75 Gallons of BMW DEF, the only issue is that my countdown is just about 24 miles! I drove it for a little bit but still bad Nox fluid code is there!!!. What I will do is to leave the engine on for about an hour or so, right now is winter in CALIFORNIA and is about 43⁰ F, so it's way too cold for this part of the state, not far from Malibu. Then I will drive it for over 150 miles hoping this thing doesn't shutdown in the middle of the freeway when the 24 miles warning runs out. So lesson learn, the sensor will catch the imbalance ratio between Urea and distilled water. You can add a little of distilled water but absolutely it won't replace the urea. Don't try it at home. Now pray for me so this stupid code goes away.

A telehandler, which i operate, has a sensor with reads the concentration of Urea in the AdBlue. It has to be a minimum of 25% according to the mechanic. But original Ad Blue has an concentration of 32.5%. So dont mess with it. It's not that expensive. And if the sensor gets broken it costs hondreds of euro's. So you don't want that either. Nice try but just put Ad Blue in the tank. Great video!

Actually looking at the fault codes would have told you how it detected a problem. Most likely exhaust sensors out of range. Similarly the dealer would look at the codes and diagnose the problem. I’m pretty sure they’d quickly work out you were putting water in it.

It's the NOx sensor that puts the MIL light on due to sensing nitrogen oxide, the vehicles I worked on, if they ran out of adblue they would go into reduced power and the fault would be registered in the ecm for six months.

Could you just reprogramme or disable the computer to bypass the AdBlu sensors?

I don't know about cars, but most Euro 6 trucks have an AdBlue quality sensor which measures the urea concentration (should be 32%) of the AdBlue in the tank, one way to measure it is the electrical conductivity. The sensor can see if it's water, AdBlue or even diesel that was filled into the tank. This type of sensor is required for the vehicle to be legislated to Euro 6, not sure of this was present for Euro 5 as well. The 250 miles indicates that the system wants to see Nox conversion to reset the AdBlue warning. Even dealerships can't just reset these as it would be illegal, all of this is described in EU law texts.

I've added some water to mine say 1-2 litres with no affect in with adblue as well Apparently it works off a boyancy system so I was contemplating trying salt water but it's best off being tried by the video author first haha then let us know adblue is so expensive now to what it was help us out 😋

I have the ultimate solution. Bought a pre-2009 diesel car with low mileage in great condition, will keep it that way, practically no depreciation, lots of power, no AdBlue nozzle, no other BS, not even a start/stop button! That should keep me going until I'm too old to have a license - love it. :-)

As stated in comments a nox sensor after the injector tests for a reduction. The tank has a level sensor to report the estimated milage and or you have run out of adblue. What surprised me was you had 55miles before the car would be imobilised. I thought it was much more. As the adblue injection only takes affect when the detected level of nox is high. When levels are reduced which will happen depending on engine load. The injection will be reduced or stopped. My car just reports I need to refill every time I start the engine. When it will give up warning I'm not sure offhand.

Try mixing some orange squash in there next time... 😅 To make it a little cloudy

Can you test again but remove the rearmost exhaust sensor? Leave it plugged in but outside the exhaust? Sounds like there will be a urea shortage so would be interested to know the ways around this.

You would have had a Nox sensor fault ( nox sensors before and after the SCR cat). Nox can't be reduced without AdBlue. Nox sensors new that the Nox emissions were to high with the water.

Surely it was a futile exercise putting "tap" water in it? 🤔. If you had used de-ionised water you would have identified if the additive in the adblue made the difference. Now, how can you be sure?.

It has a sensor that looks for what chemicals are in mix. Thats how it knows when to pump in add blue. If you put tap water in then the system its just going to keep pumping as the sensor is not picking up what the system is looking for so it pumps again.

Go to 1:36 with auto-generated subtitles. "adblue is demineralised water and 32 urethra". Sounds painful.

Brilliant information I got same problem after your video I’m very relax . Thanks

There’s most likely an emission sensor. It doesn’t know that you’ve put water in but it does know that the exhaust is coming out at a different composition than spec.

I wonder if you could mix 68% distilled water and 32% urine and fool the sensor. My 2006 F250 does not require this fluid but I am still intrigued by the possible hacks. Perhaps water, urine and amonia might work. Who knows.

just move the sensor to a sep enclosed bottle outside the system so even though the tank might have water the sensor sees ad blue then on the exhaust sensors you can put cheaters around them to shield from emissions

mechanic with 50+ years experience here. when Adblue is added to the exhaust gas stream thru the adblue injector, a chemical reaction raises the exhaust gas temperature to approx 600C which burns the soot out of the diesel particulate filter. the 2nd warning you got would be the DPF starting to block. replacing the water with adblue would create a dpf regeneration. the 650mls warning would before the dpf blocked completely.Oh, and the exhaust gas temp semsor would know that even tho the adblue injector was working, it was unable to do a regen as the temp wasn't getting high enough. PS urea is just pig piss!

i drive a smart car and have the official star (mercedes) diagnose system to read and remove faults , it can allso be used on some other mercedes vehicles and i think you can use it to turn add blue completey off i dont know wat the add blue does it , might help cleaning the sootfilter in the exhaust system , if it does that than not using the stuff might clog up the filter and cause the exhaust pressure to rise wish is wat the system would respond too with the faultcode in the dash

I’m wondering if it gets too concentrated or crystallizes out causing problems with reductant injectors or fill level sensors. I bet a flush with distilled water would fix lots of issues.

It'll be the urea quality sensor doing its thing.

The system works it out by the emissions after the catalytic converter. As the pipes will hold around 50ml of liquid it will take that long for it run through before adblu is again being injected. It's also illegal.

Lots of information on the internet about Adblue quality (concentration) sensors….and yes, there are many more parameters to measure than your suggested colour and clarity of liquids….just consider density, conductivity, refractive index, ir-absorption etc…….

Try just using deionised water in its own

Very interesting. I had this question in light of the looming Adblue shortage in Australia. There must be a chemical sensor downstream, which would explain the lag time on the fault. I get 10 000km out of a 5L amble fill on my Vito, which tells me there is a minute flow rate in the system.

Actually, it is demineralised water and UREA (not urether). Urea is used in fertiliser, among other things, but the best description I saw was in another video where AdBlue was called glorified P!$$. That's because a large part of dehydrated urine is UREA.

Basically, the sensor tests the electrical conductivity of the solution you put in. So it will have an EC tolerance level that all adblue must adhere too.

I usually top up the adblue on my Ranger as soon as I get the first warning. It typically takes it about 20 miles before it registers and resets the counter. After reading some of the comments on here, all I can suggest is to do the following: When the car tells you the Adblue is running low, it's trying to help you out. So swing by motor world and buy a bottle of it and save yourself some grief. So much simpler than trying to cheat an expensive system that was designed by someone far smarter than any of us. The alternative is to drive something other than a diesel vehicle.

Adblue is urea...what happens if you use urine?

It can use a refractometer to check the urea concentration. But also there are 2 sensors for nox in the exhaust. Before and after the catalyst, the computer knows the catalyst isnt working. These fault codes can be reset, and they become permanent faults. Permanent faults are stored in the computer, but dont put a light on the dash. After certain drive cycles with no faults, they are cleared fully. Ive seen adblue quality issues. I dont replace the parts. I replace the fluid, do a purge cycle. Then i do an stationary efficiency test, this can be performed with a scan tool. When the test passes, the codes will be inactive and I return vehicle to customer.

The AdBlue feature can be disabled in the ECU. A number of 'remapping' companies offer the service at an absolutely exorbitant price. For some vehicles an AdBlue Off emulator is available. If you are tech savvy and have ECU mapping software you can DIY the process.

I had to use the water trick for a bit but it then put the vehicle into limp mode after a while. 30 mph all the way home. No damage done once I got hold of adblue and it got through the system it ran well again. We have it on hgvs for years now. In the beginning it was hard to get hold of..

DEF system not only monitor the emissions but monitors the conductivity of the DEF tank to stop you doing what you have done. Some will log it as a permanent error code that can be detected by the vosa or an MOT testing station.

There are two NOx sensors before and after the scr catalyst. The urea reacts in the catalyst and lowers NOx which is verified by the sensors. Some of the newer tanks do have a sensor that determines urea concentrations as well.

Well done mate very good info. Cheers for that

i always wondered if you could put petrol in the tank and it would make pops when it's injected into the exhaust

It's simpler than that. The urea is needed for the DEF catalyst to do its job. Granted, I'm not in Europe. But every system I've encountered here (in Canada) has, at least, a temp sensor in the DEF cat. More modern ones have a NOx sensor before and after the DEF cat. No temperature rise in the cat, error light. No reduction in NOx readings at the rear sensor, error light.

I would have recommended the use of distilled or deionized water, to avoid leaving calcium or other dissolved minerals in tap water in the SCR. Those minerals can foul the catalytic substrate in the SCR, reducing its effectiveness. Another thing to try, is to see how much you can dilute the def with purified water, before the system realizes, that there isn't enough uric acid, to be effective. I'm sure there's some tolerance, because of deterioration of DEF over time. These systems actually have NOx sensors in the exhaust train, that can tell the difference between treated and non-treated exhaust, and if they don't see the difference they're looking for, the computer will "throw a code". My guess is, that the code will show that the SCR is defective, because of not reducing NOx, despite the injection of DEF.

Diesel forklifts using a scrubber tank filter the exhaust through water only and is clean enough to operate inside, so it should work

I drove a truck with adblue and bye accident I pulled the main fuse for the adblue and it still worked perfectly and never used any for months saved a fortune.

In caterpillar equipment it has a sensor that can read the percentage of urea in the water.

It is the NOx sensor that detects that NOx has not been converted to N and H2O (because there is no ammonia in the catalytic converter to react with NOx).

Issues with doing that, you'd void any warranty or parts insurance on the vehicle, if it did work you get limescale build up on the feed and everywhere else, this could in turn damage sensors as well.

Did it many moons ago on my Merc truck when it ran low on adblue, top up with water and away you go until you get proper sheep’s piss in it and nothing was harmed in the process 😊

There's a quality sensor at the bottom of the tank unit. Its 2 eyes opposite each other. One of the eyes fires a light beam across to the other eye and the light refracts off the water particles in the "adblue" and depending how much light it recieves at the other eye it knows the quantity of water to urea in the adblue. The content should be 67.5% water and 32.5% urea 👍

It's monitoring the particulates before and after the cat. And measures the pressure in the cat and exhaust and then it figured it out. For example. If the pressure in the cat is normal it means the filter is clean. But the exhaust isn't changing. It means the aftertreatment has an issue. Ie Adblue dosing fault

Most vehicles will tell the difference between two clear liquids from the NOx sensors that measure the conversion efficiency. There is a sensor before the DEF injector that works out how much DEF needs to be injected to convert the NOx and then there is a sensor after the catalysts that checks the conversion has been successful. By using water, there is no conversion so the system registers a fault. Heavy duty applications can have a DEF quality sensor, which can detect water from DEF before the engine is even started. They bounce an ultrasonic beam across a known distance and measure the time it takes to return, from that you can calculate the density of fluid, and DEF has a different density to water. DEF systems are heavily legislated to make sure they cannot be bypass as they are emissions critical, the manufacturers will have tried everything you can think of to bypass the system.

Try pising in the tank 60% uru

There is no chem. lab in the AdBlue tank. The car does not know it‘s AdBlue, Water or something else. But after the AdBlue injection is a sensor. With water you haven’t got the catalytic reaction. Therefor the fout massage in the display. After the rest of the water is gone (still in the pipe/tab) the system is working again and the fout massage disappears. If you don’t want to use or pay for AdBlue you must „update“ the program in you engine control unit. But that’s illegal in most of the countries. Regards from Belgium

It's after getting pricy now, it's gone up over 100%, it's the same price as petrol here in Ireland. I can't see how they can justify the price hike, Urea is cheap as chips. Be great if you could do a video on manufacturing the solution, it can't be that difficult with some advice from a chemist. Definetly something I'm going to look in to myself.

Cant you use a mixture of RO water and wee? Adblue has urea as the active ingredient, and wee is full of urea, plus wee is a lot cheaper than adblue!

As the active ingredient of Adblue is urea, and urea is the main(?) component of urine, I wonder what happens if you urinate into the Adblue tank...?

yes it can tell the difference, there's a ultrasonic sensor in the tank that measures the quality

When Australia recently had a ADBLUE shortage , i know of truck drivers that where putting piss & purified water through coffee filters . & the system dident know th difference . The truck keept working just fine...

I do add blue faults ,first thing putting water in instead of add blue won't work, it would put out a low add blue level ,that's it ,in ur exhaust system there are 2 nox sensors one b4 and one after add blue injector point ,an algorithm is used within the acm and add blue level sensor, to work out if add blue is working in reducing nox .since the acm can see us ab level go down and no reduction in nox it will flag a fault ,normally, poor add blue quality ,this in ur case took a few hundred miles to work out minimum ab quality threshold usually around 12% . Put simply if you want to run on water full time you can, but you will require a good diagnostic computer ,simply reset addblue concentration value to 32% each time eml comes on ,but it's probably easier to just use add blue ,hope this helps

Wonder what would happen if you mixed it 50 adblue/50 water

Adblue contains urea which has -NH2 groups in its molecule. It reacts in the catalyst to split the oxygen atoms from the NOx to make water and nitrogen. Sensors downstream check the level of NOx in the exhaust to ensure the adblue dosing pump is working correctly. They figure out something is wrong because the NOx content in the exhaust is still high and on comes the warning light.

The probe looks for the correct conductivity of the fluid. Either use adblue or electronically delete.

Interesting video and we know ad blue is the way to go!!!

The sonic sensor will detect the liquid density, most likely sending out a pulse and a receiver returning a time the pulse travelled, thicker liquid longer time...

Most likely a corrosion sensor bar , water has minerals that scale , the actual proprietary solution must have some sort od anti scaling and corrosion inhibitors.

I have always wanted to try this, but I didn't because I was scared of the possible cost if it failed. a good job was done all the same you have answered my thoughts

"Urethra" : the tube connecting your bladder to the outside world "Urea" A compound CO(NH2)2 that decomposes to ammonia NH3 and reacts with NOx compounds in the exhaust. It can tell as there is a sensor that detects NOx in the exhaust and will add amounts of adblue liquid until the NOx reduces to tolerances, so when you add water to the tank it cannot add it fast enough to reduce the NOx regardless to the amount it can add - so throws a fault. You cannot completely drain the tank and injectors into the exhaust, and it would take 250 miles to clear out the water until the sensors can detect the drop in NOx

The AdBlue system could be connected with the NOC sensor in the computer / ECU maybe, as in: If the NOC emissions are too high, it’ can’t be AdBlue?

My friend put water in Vivaro van on lease for over a year before it wnt into limo mode . Vauxhall hall it and couldn’t find the fault . They said the had everything and everyone to fix it to no avail ! They said it hadn’t ever been seen before and whilst this was being repaired the one they borrowed him done it too as it was water in that too!

I've never had to buy AdBlue because when I was driving trucks that required it, the company paid for it, so I have no idea what it costs per 20-litre drum. I wonder if there is anyone brave enough to try dissolving fertilizer-grade urea into water at the correct ratio to see if it would be viable and cheaper than buying the regular AdBlue.

I had a euro4 truck '57 plate that never used any addblue in 2 and 1/2 years ! No limp mode, no warning lights, went thro plate no problem. Its replacement drank addblue, blew turbo, always showing lights or going into limp mode or just stopping and mostly needed re programming supposedly. I never knew if i was going to get home or have to stay out another night.