AdBlue is a substance that is engineered to reduce nitrogen oxide (NOx) emissions in diesel engines. It’s a clear liquid that is sprayed into the exhaust before the point of emission. When used for regular road vehicles, it shouldn’t cause any problems, as long as the manufacturer’s instructions are followed.
AdBlue is required for all commercial diesel vehicles that weigh over 7.5 tonnes, and are fitted with Selective Catalytic Reduction (SCR) technology. It is fitted as standard on most diesel vehicles manufactured after October 2006. It’s a clean, non-toxic substance, that is non-flammable.
AdBlue works by a SCR process. It squirts tiny amounts of ammonia into the exhaust, which react with the harmful NOx gases, converting them into nitrogen and water. It contains about two-thirds deionised water and one third high purity urea, which is the substance that contains the ammonia.
AdBlue is held in a separate tank within the vehicle, and must not be mixed with the diesel fuel in the tank. This could cause serious harm to the engine. Unless you drive a significant number of miles, it only needs to be topped up on average twice a year, or less if you have a low milage. A warning light will appear when the levels are low.
However, for anyone running a large fleet of commercial heavy vehicles that cover long distances on a daily basis, the AdBlue will need topping up much more frequently. This can amount to a significant expense for a business owner.
If the vehicle has run out of AdBlue, the system is designed so that the vehicle won’t start until it is refilled. It may otherwise enter limp mode, so that the engine power is reduced, and it can’t be driven at higher speeds. The problem is more likely to affect vans, HGVs, and heavy plant vehicles, as there is more scope for faults within the system to occur.
For the majority of diesel cars, AdBlue can be run with no problems. However, when used on a construction fleet, which tend to make more short journeys at low speeds, the SCR system is prone to developing faults. This is why many heavy plant vehicles employ AdBlue removal methods, such as disabling the SCR system.
Because AdBlue freezes at temperatures of below -10°c, it can cause problems in colder countries. The fluid may freeze in the system, which will cause the low-power mode to kick in, or even prevent the vehicle from starting altogether. Once damaged in this way, the system will need significant repairs before the vehicle will operate.
The AdBlue system can be bypassed. This is done by fitting an AdBlue emulator box, which can be done in approximately one hour by a specially trained mechanic. Problems with SCR systems are not only expensive to fix, but they take the vehicle out of use, and waste valuable time that could have been spent more profitably.
Therefore, for off-road vehicles, or vehicles that are to be exported outside the EU or UK, deleting or disabling the AdBlue system is a good solution to avoid costly downtime.