What is AdBlue and what is a Denoxtronic system?

What is AdBlue and what is a Denoxtronic system?

Read below to find out more…



AdBlue is the most commonly used Diesel Exhaust Fluid (DEF) and is a solution of 32.5% urea and 67.5% of demineralised water. AdBlue is now mandatory in all diesel engines manufactured after the introduction of the Euro 6 Emissions Standard due to the European Union and other emissions regulators stating that ‘nitrogen oxide must be reduced’.

Nitrogen oxide is a combination of nitric oxide and nitrogen dioxide and is produced when nitrogen and oxygen are bonded together, which is a by-product from the combustion process occurring under high pressures and temperatures in the combustion chamber. Although nitrous oxide occurs naturally as part of the Earth’s nitrogen cycle, human activity now contributes up to 40% of all nitrogen oxide in the atmosphere.

Only diesel engines require AdBlue as petrol engines, typically, all have efficient catalytic converters fitted and can be run at lower combustion temperatures by various methods that reduce the levels of nitrogen oxide. AdBlue is needed by your diesel vehicle as much as diesel is needed, therefore it will not run without it.

When levels of AdBlue are running low, a dashboard warning light will appear when there are approximately 1,500 miles of fluid left in your tank, giving you enough time to replenish the AdBlue levels. However, if the warning light is ignored and the AdBlue tank is allowed to run dry, your vehicle will enter the ‘limp home mode’ and the engine will be unable to restart after it has been switched off.


How to refill or top up AdBlue

  1. Locate the vehicle’s AdBlue tank – depending on the make and model of your vehicle, the AdBlue tank filler neck can be located: next to the diesel filler neck; somewhere under the bonnet in the engine compartment; or, somewhere in the boot. If you are unsure, check your owner’s manual.


  1. Attach an anti-spill nozzle to the AdBlue container. If you do not have an anti-spill nozzle, you can remove the AdBlue tank cap and place a funnel in the top of the AdBlue container.


  1. Refill the AdBlue slowly.


  1. If required, perform a dashboard reset to remove the AdBlue warning light. If you are unsure whether this applies to your vehicle, check your owner’s manual.


  1. After refilling the AdBlue, do not start the vehicle engine until the AdBlue refill has been validated by the vehicle’s computing system and the AdBlue warning light (if previously shown) is cleared. Once confirmed, you are ready to go. If the light does not clear, this could indicate an issue with the system. If unsure, ask a professional for help.


AdBlue Myths

  • It is made of pig urine’ – FALSE: the urea used in AdBlue is a high purity man-made solution. Pig urine, or any urine for that matter, would not be pure enough or sterile enough for a commercial product. Urea is a chemical compound found in both animal and human urine, however it is found in much, much lower concentrations than the urea used in AdBlue.
  • You can make your own AdBlue solution’ – FALSE: the urea used in AdBlue is of very high purity and is dissolved into deionised water, meaning that over-the-counter urea in demineralised water will not suffice. Any makeshift AdBlue solutions will not be of the same quality and could cause significant damage to your vehicle.
  • AdBlue is toxic’ – FALSE: AdBlue is non-toxic and is perfectly safe when used in the correct conditions. However, it is still a specialised mixture for chemical reactions within the exhaust system, so it should not be used for any other purposes. Also, water is the primary ingredient, so it may be corrosive to certain metals.
  • You don’t need AdBlue’ – FALSE: any diesel vehicle manufactured after the introduction of the Euro 6 emissions standards will not be able to run without both diesel and AdBlue.
  • AdBlue still causes pollution’ – FALSE: many scientific studies have found that SCR technology can reduce fuel consumption by approximately 5%, meaning lower CO2 When bringing AdBlue into the mix, harmful gases (nitrogen oxide, particulate matter, carbon monoxide, and benzene) are significantly minimised, which also allows the requirements to meet Euro 4, 5 and 6 emissions standards.


Bosch Denoxtronic Systems

The Bosch Denoxtronic System is an important metering system in commercial and off-highway vehicles as it controls and doses the injection of AdBlue into the exhaust gas stream. In line with the operating state of the engine and the emission values, the correct amount of AdBlue is atomised and injected into the exhaust stream. The urea into ammonia through thermolysis and hydrolysis. A chemical reaction also occurs in the Selective Catalytic Reduction (SCR) catalytic converter as the ammonia reduces the nitrogen oxide to water and nitrogen.

Today, there are approximately 14 million Denoxtronic systems built into cars and light commercial vehicles across the world.

Historically, nitrogen oxide emissions of modern diesel engines are 96% lower than those of a typical diesel vehicle from 1990.


Denoxtronic Main Components

  • Denoxtronic Supply Module: reduces the nitrogen oxides into the exhaust system
  • Denoxtronic Dosing Control Unit: controls and monitors all functions and active components in the exhaust-gas treatment system
  • NOx Sensor: regulates and diagnoses the catalytic nitrogen oxide reduction
  • Denoxtronic Dosing Module: provides AdBlue for the exhaust system
  • Differential Pressure Sensor: measures the pressure drop between two points in the flow pattern
  • Particulate Matter Sensor: monitors the function of the diesel particle filter (DPF)


Bosch Denoxtronic (PC-LCV) Main Failure Reasons

  • Malfunction:
    • Supply module and/ or heating pot
  • Effect:
    • No AdBlue injection/ low AdBlue injection
    • No pressure build-up
  • Reason:
    • Blocked filter in supply module (no exchange possible)
    • Malfunction diaphragm pump of supply module
    • Malfunction valve of supply module
    • Malfunction pressure sensor of supply module
    • Malfunction level/ temperature sensor in heating pot
    • Malfunction heating function in heating pot


Bosch Denoxtronic (PC-LCV) Main Failure: Diagnosis

  • Malfunction:
    • Supply module and/ or heating pot
  • Effect:
    • No AdBlue injection/ low AdBlue injection
    • No pressure build-up
  • Diagnose:
    • Vehicle diagnose with KTS (service level “On Vehicle”)
  • Tools:
    • Suitcase Denoxtronic PC/ LD (for on-/off-board diagnose)
    • Holder tank unit for work bench
    • Tools for disassembling/ assembling heating pot


Advantages of Bosch Denoxtronic Systems

  • Reduction of harmful nitrogen oxide emissions by up to 95%
  • Contributes towards achieving Euro 6 emissions standards
  • Engine operation can be optimised towards fuel efficiency (fuel savings up to 5%)
  • Due to the use of the SCR system, fuel consumption is reduced and, thusly, CO2 emissions are reduced
  • Proven, robust Bosch technology
  • Small mounting space – the Supply Module can be integrated into the AdBlue tank.


Bosch Denoxtronic Filters

Bosch Denoxtronic filters protect the Denoxtronic system by removing particles from AdBlue, thus contributing to optimum dosing. Denoxtronic filters should be replaced regularly according to the vehicle manufacturer’s specifications.


Advantages of Bosch Denoxtronic Filters

  • Frost resistance due to compressible compensation element with sealing function as AdBlue freezes and expands at just -11°C. The compressible compensation elements prevent damage to both the filter and the supply module
  • High particle separation rate due to microporous filter medium
  • Chemical resistance to AdBlue due to usage of high-quality materials
  • High particle holding capacity due to larger filter surface


How to replace a Denoxtronic Filter

Denoxtronic filters should be replaced regularly according to the vehicle manufacturer’s specifications:

  1. Locate the Denoxtronic supply module covering the Denoxtronic filter


  1. Unscrew the housing cover of the Denoxtronic filter


  1. Remove the Bosch compensation element


  1. Use the extraction tool to remove the Denoxtronic filter – observe the colour coding of the extraction tool: the black filter end cap uses the side imprinted ‘black’, and the grey filter end cap uses the side imprinted ‘grey’


  1. Fit the new Denoxtronic filter


  1. Fit a new Bosch compensation element


  1. Re-screw the housing cover of the Denoxtronic filter


Denoxtronic Diagnostics

Below are some examples of the Denoxtronic Diagnostics Tools and Software offered by Merlin Diesel Systems Ltd:

  • KTS 560
  • KTS 590
  • ESI[tronic]

Click on the images below to be directed to the corresponding webpage:


KTS 560

The KTS 560 is a diagnosis module manufactured to speed up workshop operations, improve accuracy and enhance potential.

The KTS 560’s PassThru interface enables easy reprograming of vehicle manufacturer software and has the ability to run parallel diagnosis.


KTS 560 Features & Benefits

  • Built-in 1-channel multimeter: quick and convenient way to resolve issues with voltage, current and resistance
  • Ethernet-interface (DoIP – Diagnostics over Internet Protocol): supports current and future vehicle interfaces based on Ethernet
  • Compatible with Bosch Easy Connect and other Bosch vehicle-specific adapters
  • Powerful and stable 100 m-range Bluetooth connectivity
  • Optimally designed to use ESI[tronic] 2.0 Online software (purchased separately): troubleshooting and support for rapid repair and maintenance
  • Works on any Windows PC with ESI[tronic] 2.0 Online installed and licensed


KTS 590

The KTS 590 is a communication module that ensures the most advanced ECU diagnosis for Ethernet-based DoIP (Diagnostics over Internet Protocol) vehicle interfaces to significantly enhance workshop output.

With the KTS 590, technicians can efficiently test and measure all sensor and actuator signals, and quickly and effectively evaluate voltage, resistance and current.


KTS 590 Features & Benefits

  • Built-in 2-channel oscilloscope: benefit from real-time viewing of electrical signal variation for highly precise testing of complex electrics
  • Built-in 2-channel multimeter: locate and fix electrical issues quickly
  • Fully PassThru compliant: access and reprogram vehicle manufacturer control unit software for efficient daily workshop routines
  • Parallel diagnosis: the KTS 590 module can communicate with up to three CAN and K-Line interfaces simultaneously enabling fast and productive diagnosis
  • 100 m-range Bluetooth connectivity
  • Supports Bosch Easy Connect and other Bosch vehicle-specific adapters
  • Optimally designed for ESI[tronic] 2.0 Online software (purchased separately): troubleshooting and support for rapid repair and maintenance
  • Works on any Windows PC with ESI[tronic] 2.0 Online installed and licensed


Bosch ESI[tronic] Software

Merlin Diesel Systems Ltd offer a multitude of applications for Bosch ESI[tronic] Software.

The ESI[tronic] online diagnostic software enables fast, efficient and effective maintenance, service and repairs, as well as the performance of comprehensive diagnostics to find the correct repair solution and rectify errors.

Please see attached software price list below:



For more information, visit our dedicated Bosch Software blog:





Here are a few of our latest posts to read up on:



Keywords: Merlin, Merlin Diesel Systems, Diesel, fuel, Denoxtronic, Bosch, Bosch Denoxtronic, Bosch Denoxtronic Systems, AdBlue, software, filters, Denoxtronic filters, diagnostics, Bosch diagnostics, Diesel Exhaust Fluid, DEF, emissions, emissions standards, How to refill AdBlue, How to replace a Denoxtronic Filter


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