Testing and Diagnostic Equipment for SCR and AdBlue® Systems

Frequently Asked Questions About Diagnosing SCR and AdBlue® Systems

SCR systems are a key component of modern diesel exhaust aftertreatment. A reliable diagnosis involves not only diagnosing the electronic control units but also checking AdBlue® quality, system pressure, system integrity, flow, and dosing.

• What does SCR stand for?

  SCR stands for Selective Catalytic Reduction.
  
  In this exhaust aftertreatment process, a urea-water solution is injected into the exhaust stream.
  
  The urea produces ammonia, which reacts with the nitrogen oxides in the SCR catalyst. This converts the nitrogen oxides primarily into nitrogen and water.

• What is AdBlue®?

  AdBlue® is a specially formulated urea-water solution for SCR systems.
  
  It consists of approximately 32.5 percent high-purity urea and water.
  
  The solution is stored in a separate tank in the vehicle and is injected into the exhaust stream by the SCR system as needed.

• What components make up an SCR system?

  The exact configuration varies depending on the vehicle and manufacturer.

  Typical components include, for example:

  • AdBlue® tank
  • Feed or supply module
  • Pump
  • Hoses
  • Pressure regulator
  • Dosing module or injector
  • SCR catalyst
  • Temperature and NOx sensors
  • Electronic control unit

  A fault in a single component can affect the operation of the entire system.

• What tests can be performed on an SCR system?

  Depending on the symptoms, various tests may be appropriate.

  These include, for example:

  • Measuring SCR system pressure
  • Checking delivery pressure
  • Checking the system for leaks
  • Measuring AdBlue® concentration
  • Testing the AdBlue® sample for contaminants
  • Draining the tank or system
  • Filling the system
  • Cleaning or flushing the dosing and supply modules

  The mechanical inspection can be supplemented by an electronic vehicle diagnostic check.

• What is the correct AdBlue® concentration?

  AdBlue® has a urea content of approximately 32.5 percent, in accordance with standards.
  
  A concentration that deviates significantly from this may indicate that the fluid is unsuitable or has been altered, and may impair the function of the SCR system.
  
  The concentration of a sample can be checked using a suitable refractometer.

• How is the AdBlue® concentration measured?

  A simple laboratory method involves taking a measurement using a refractometer designed for this purpose.
  
  A small sample of the urea-water solution is placed on the measuring surface.
  
  The concentration can then be determined using the corresponding scale.
  
  Leitenberger offers both individual refractometers and complete analysis and testing kits for this purpose.

• Why should AdBlue® be tested for contaminants?

  Contaminants can impair the function of sensitive SCR components.
  
  Therefore, in cases where the nature of the fault is unclear, it may be advisable to check not only the concentration but also the condition of the fluid.
  
  For example, the Leitenberger AEKP09_LR analysis kit allows you to test not only the concentration but also whether the AdBlue® solution has been contaminated by diesel fuel.

• Can AdBlue® expire?

  The quality of a urea-water solution can be affected by storage conditions and duration of storage.
  
  In the event of prolonged or improper storage, the quality or concentration should therefore be checked if there is any reason to suspect a problem.
  
  The assessment should be based on the specified test method and, if applicable, the manufacturer’s specifications.

• How is the SCR system pressure checked?

  A suitable pressure or pressure/vacuum tester is connected to the system via the designated SCR connections.

  Next, check the pressure that builds up in the delivery or metering system.

  The measured values must be compared with the specifications provided by the respective vehicle or system manufacturer.

  Leitenberger offers analog and digital testers as well as complete SCR diagnostic kits for this purpose.

• What is the normal pressure in an SCR system?

  There is no universally applicable SCR system pressure for all vehicles.

  The target value depends, among other things, on:

  • System manufacturer
  • Vehicle
  • Delivery module
  • Dosing system
  • Operating conditions

  The measuring range of the test device must therefore not be confused with the vehicle’s target value.

  The relevant manufacturer’s information is always authoritative.

• What could be the cause of low SCR system pressure?

  Possible causes may include, for example:

  • faulty feed pump
  • leak
  • restricted flow
  • defective connection
  • faulty pressure control
  • problem in the supply module

  To narrow down the cause, a pressure and leak test of the SCR system can be performed in addition to the electronic diagnosis.

• How is an SCR system tested for leaks?

  The system is connected using a suitable AdBlue®-compatible test device.
  
  You can then check whether the specified system pressure is being built up and maintained.
  
  A loss of pressure may indicate a leak in the test setup or in the SCR system.
  
  Pipes, connections, supply, and metering components should then be inspected in accordance with the manufacturer’s specifications.

• Why do SCR testers need to be AdBlue®-resistant?

  AdBlue® places special demands on the materials used.
  
  Therefore, only equipment, hoses, seals, and fittings that are expressly suitable for the urea-water solution should be used.
  
  The Leitenberger FP 07_AB kit, for example, is designed to be AdBlue®-resistant and free of non-ferrous metals.

• What are AdBlue® crystals?

  If a urea-water solution dries on a surface or in a system component, solid white deposits may form.
  
  Depending on their location, such deposits can affect lines, connections, or dosing components.
  
  When diagnosing the problem, therefore, not only should the electronic error code be checked, but also the actual condition of the dosing and delivery system.

• When does an SCR system need to be cleaned or flushed?

  Depending on the system and the nature of the malfunction, flushing or cleaning may be necessary—for example, if deposits or contaminants are suspected in lines or modules.
  
  Leitenberger offers special cleaning and diagnostic kits for various commercial vehicle, agricultural, construction, and material handling applications.
  
  Whether a system may be flushed and how the process is carried out depends on the manufacturer’s or service provider’s specifications.

• Can the SCR system be refilled with AdBlue® after a repair?

  Yes, provided that the repair is complete and the system has been properly prepared.
  
  For certain vehicles, controlled filling can be performed using a suitable filling unit.
  
  The Leitenberger ABE 03_LR, for example, operates using the gas-pendulum method and requires neither electricity nor compressed air.

• Why is it important to ensure cleanliness when filling?

  Contaminants can damage sensitive components of the SCR system.
  
  Therefore, only clean, designated containers, connections, and filling devices should be used.
  
  Mixing with fuel, oil, or other operating fluids must be avoided.

• Can AdBlue® be siphoned out of the tank?

  For maintenance and repair work, suitable extraction devices that are explicitly AdBlue®-resistant may be used.
  
  Leitenberger offers, among other things, a vacuum box and electric extraction pumps in 12-V and 24-V versions.
  
  Such devices are suitable, for example, when an SCR tank needs to be emptied for repair or service work.

• What is a Denoxtronic system?

  Denoxtronic is a family of SCR systems from Bosch.
  
  The system includes, among other things, delivery, metering, and control components for the on-demand injection of the urea-water solution into the exhaust stream.
  
  Leitenberger offers special service and test kits for certain Denoxtronic systems.

• Can a diagnostic tool alone determine whether the SCR pump is functioning properly from a mechanical standpoint?

  Not always.

  An electronic diagnostic system can provide ECU information, error codes, and sensor readings.

  A separate pressure measurement can also show the actual delivery or system pressure generated by the hydraulic system.

  Especially when a pressure reading is implausible, combining electronic and mechanical diagnostics is advisable.

  For commercial vehicles and machinery, this can be combined, for example, with the Jaltest Multi-Brand Diagnostics.

• What should be checked if an SCR error occurs repeatedly?

  Depending on the fault symptoms, a systematic diagnosis may include the following points:

  • Fault memory and actual values
  • AdBlue® level
  • AdBlue® concentration and quality
  • SCR system pressure
  • System tightness
  • Hoses and connectors
  • Pump module
  • Dosing module
  • Sensors
  • Condition of the exhaust aftertreatment system

  This prevents individual components from being replaced based solely on a fault code.

• What kind of SCR testing equipment is appropriate for a repair shop?

  For professional SCR service, the following items may be particularly useful, depending on your vehicle fleet:

  • Analog or digital SCR pressure tester
  • Pressure and leak test kit
  • Refractometer for AdBlue®
  • AdBlue® analysis kit
  • Diagnostic or cleaning kit
  • Filling unit
  • Suction device

  For workshops servicing trucks, agricultural machinery, or construction equipment, specialized cleaning and service kits may also be useful.

  You can find additional mechanical test equipment under Test and diagnostic equipment for exhaust systems.