Why you shouldn’t disable your truck’s AdBlue system

Since the late-1980s truck engine makers around the world have progressively cleaned up their emissions act. In so doing, performance and fuel economy have improved out of sight, but the complexity of emissions systems has increased.

Although successive Australian Federal Governments haven’t adopted state-of-the-art emissions reduction legislation, the rest of the developed world has.

While Australia sticks with Euro 5 and its international equivalents, Europe, the USA and many other governments have adopted Euro 6 and its equivalents.

An absolutely critical part of Euro 6 compliance is reduction of oxides of nitrogen (NOx) through the use of exhaust after-treatment in the form of selective catalytic reduction (SCR).

Also, many Euro 4 and 5 heavy truck engines, dating back as far as 2005, have SCR and rely on AdBlue as well.

Essentially SCR squirts a jet of AdBlue, or an equivalent diesel exhaust fluid (DEF), into a muffler-like appendage in the exhaust system.

The chemical exchange that happens in there converts harmful NOx that’s responsible for acid rain and a host of other nasties into harmless nitrogen (N2) and water (H2O).

The internet is full of suggestions about alternatives to correctly formulated DEFs and all of them are stupid or dangerous. The most common advice is to wee in your AdBlue tank! That one comes from the fact that AdBlue contains urea and so does human urine.

Related reading:
Why the AdBlue shortage?
Advice: Driver's guide to DEF (AdBlue)
What is DPF and how does it work?

The ever so slight problem with this argument is that urea concentration in urine is around 2.5 per cent, while in AdBlue it’s 32.5 per cent. Weeing in your AdBlue tank won’t work and, if there’s any corrosive DEF deposit around the neck of the AdBlue tank, it could mean a trip to hospital, for some embarrassing after-treatment on your own exhaust system!

The complexity of diesel emissions systems has spawned an illegal aftermarket sub-culture in their bypass or removal. All these procedures are non-compliant with ADRs and international emissions laws.

The common bypass systems negate exhaust gas recirculation (EGR) that’s designed to keep combustion temperatures lower and reduce NOx production; hollow-out the filtration medium in a diesel particulate filter (DPF) and, more recently, employ modules that cancel operation of the selective catalytic reduction system (SCR).

The sneakier cheat devices retain all the manufacturer’s hardware and pass casual compliance inspection: EGR valves are left in place, but are blanked-off; DPFs are retained but have no ‘guts’ – literally – and AdBlue hardware looks intact, but hides a module that cancels operation.

Critical to these SCR ‘tuning’ services are methods of ‘fooling’ the vehicle’s computers into thinking that all is functioning normally. The common name for some of them is ‘emulator’, indicating that they mimic the SCR system operation, without actually doing so.

Here is a quote from one such tuning service’s website: “The AdBlue and SCR system is a relatively complex system with an array of electronic sensors, modules and pumps that can fail and can be expensive to maintain.

“A vehicle which is used on a regular basis will consume a large amount of AdBlue and the tank will need to be refilled on a regular basis. Our AdBlue delete service will electronically disable the AdBlue system, along with removing the associated dashboard lights and warning messages.

“Disabling the AdBlue system is normally completed by reprogramming the engine management system, however some vehicles will require a small electronic unit to be hardwired into the vehicle.

“Our AdBlue delete service is strictly sold as an off-road-use-only product, driving your vehicle on the road with an AdBlue delete could result in prosecution.”

Yet another website claims that after having its EGR, DPF and SCR systems disabled an engine reverts to Euro 3 compliance, so it’s not such a serious emissions issue. However, we couldn’t find a single instance of diagnostic testing that proved such a claim.

Two diesel engine makers we spoke to strongly disagreed with this claim, pointing out that various engine operating parameters work in concert to meet emissions regulations.

For example, ‘High-SCR’ engines have a ‘hot’ combustion process that results in very low amounts of particulates (Pm) in the combustion chamber, but with high amounts of NOx. Such an engine relies on SCR to ‘scrub’ this NOx from its exhaust gases. Disabling the SCR system does not make this engine compliant with Euro 3 or any other regulation.

Of course, the unscrupulous suppliers of ‘cheat’ devices are emboldened to some extent by the actions of vehicle makers themselves. There have been several well-publicised incidents of manufacturer-installed ‘cheat’ devices or programming that have cost them billions in fines, but reports keep coming.

The most recent is a November 2021 accusation against Mercedes-Benz over tested diesel vehicles producing up to 500-per cent more NOx than they should legally, because of SCR operational issues.

So if you’re considering mucking around with your truck’s SCR system, or if one of your mates says it’s okay to do it, think again. It’s not only highly illegal, it could also damage your truck.