After several weeks of hot weather, has your vehicle suddenly displayed an SCR or AdBlue fault?
The problem does not always come from the catalyst itself. After summer, high temperatures, AdBlue deposits and certain sensors can affect the operation of the SCR system.
A methodical inspection can often help identify the cause more quickly and prevent the unnecessary replacement of expensive components.
Why Does the SCR System Need Special Attention After Summer?
The SCR – Selective Catalytic Reduction system helps reduce NOx emissions by injecting AdBlue into the exhaust gases.
It relies on several components working together:
- AdBlue dosing injector
- Pump and supply circuit
- NOx sensors
- Temperature sensors
- Wiring harnesses and connectors
- SCR catalyst
- Engine control unit
When just one of these components sends incorrect information, the system may trigger an engine warning light, an emissions fault or even reduced vehicle performance.
1. Watch for AdBlue Crystallisation
One common problem is the appearance of deposits or crystals around the AdBlue injector.
This can occur when the AdBlue is not sprayed correctly or when temperature conditions prevent the fluid from being properly converted.
Key signs to check include:
- white deposits around the dosing unit;
- poor spray pattern;
- partial injector blockage;
- AdBlue dosing faults;
- insufficient SCR efficiency.
Before replacing the dosing unit, it is therefore important to inspect its condition and check the system values.
2. Check the NOx Sensors
NOx sensors play an essential role in SCR system operation.
They measure emissions before and after the catalyst, allowing the ECU to adjust AdBlue dosing.
A faulty sensor may send an incorrect value even when the catalyst itself is operating correctly.
Technicians should check:
- stored fault codes;
- NOx sensor readings;
- electrical supply;
- connectors;
- wiring;
- consistency between upstream and downstream measurements.
3. Don’t Forget the Temperature Sensors
AdBlue dosing also depends on exhaust gas temperature.
Incorrect information from a temperature sensor can therefore affect the operation of the SCR system.
Before carrying out a major repair, compare the measured values with the technical specifications provided for the vehicle.
Jaltest INFO Web in Action
When facing this type of problem, Jaltest INFO Web helps technicians move from a simple fault code to a structured troubleshooting process.
Depending on the vehicle, the platform can provide access to:
- fault code information;
- wiring diagrams;
- component locations;
- connectors and pinouts;
- technical reference values;
- inspection and repair procedures.
For example, when dealing with a NOx sensor fault, the technician can identify the sensor location, consult the wiring diagram and check the necessary technical information before deciding whether the component really needs to be replaced.
The principle is simple: confirm the cause before replacing the component.
A Simple Method for Diagnosing an SCR Fault
- Read and record the fault codes.
- Check the AdBlue level and condition.
- Visually inspect the SCR dosing unit.
- Look for signs of crystallisation.
- Check the NOx and temperature sensors.
- Inspect power supplies, grounds and connectors.
- Compare measured values with the technical data.
- Follow the manufacturer’s procedure before carrying out repairs.
Conclusion
After summer, an SCR fault can have several possible causes: crystallisation, the AdBlue injector, a NOx sensor, temperature-related issues or an electrical fault.
Replacing the first component mentioned by a fault code can waste both time and money.
With Jaltest INFO Web, technicians have access to the information they need to understand the system, check the relevant components and work towards a more accurate diagnosis.
