An emissions fault occurs when the pollutants a vehicle produces exceed the permitted level. Sensors fitted at the inlet and outlet of the catalytic converter and the diesel particulate filter measure the concentration of harmful substances; when the system can no longer filter effectively, emission values rise and the vehicle logs a fault.
Because exhaust gas is harmful, emissions testing is regulated by law and must be carried out on a set schedule. It is worth checking these values before the vehicle goes for inspection.
Why Does the Emissions Light Come On?
There are two common causes:
- Failure of one of the sensors feeding the system (lambda, NOx, differential pressure, temperature)
- A fault in the EGR (Exhaust Gas Recirculation) valve
The EGR system routes part of the exhaust gas back to be burned again, keeping emission values down. When it fails, the emissions warning lamp lights.
Symptoms of an EGR Fault
| Symptom | Cause |
|---|---|
| Loss of pulling power | Combustion efficiency drops and the engine cannot make the expected power |
| Increased fuel consumption | Reduced efficiency needs more fuel for the same work |
| Slow starting or misfiring | Incorrect gas recirculation upsets the mixture |
| Sooty, dirty exhaust smoke | Carbon build-up and incomplete combustion |
| Emissions warning lamp | The ECU sees the system missing its target values |
EGR Valve: Clean or Replace?
Once the fault is confirmed, the EGR valve must either be cleaned or replaced.
Replacement is rarely the first choice, for two reasons:
- It is expensive.
- Unless the underlying cause is addressed — soot production, short-journey use, a blocked DPF — the same problem returns.
Cleaning, combined with fixing the root cause, should be tried first.
Why DPF Cleaning Matters
Exhaust gas is measured by sensors at the inlet and outlet of the diesel particulate filter. If the filter is blocked, those sensors read high and the system sets a fault. This is why DPF cleaning directly resolves many emissions faults — once the filter is clear, the measured values return to normal.
Emissions Solutions at Nitro Bilişim
We provide this service at the garages in our head office and other branches. The work is carried out with the Flex programming tool from Magicmotorsport, for whom we are the distributor: the file is read from the ECU when the vehicle arrives, and the revised software is written back.
An important note: solutions that disable emissions hardware (DPF, EGR or AdBlue delete) are contrary to emissions regulations on road-going vehicles and will cause a failure at inspection. Such solutions are intended for racing, off-road and closed-course use. On a road vehicle the lasting fix is to genuinely repair the sensor, valve or filter.
You May Also Like
What Is a Diagnostic Tool? How Does It Work?
