The EGR (Exhaust Gas Recirculation) is an anti-pollution system that recirculates a percentage (5-30%) of the exhaust gases in the intake manifold. The cooled exhaust gases lower the combustion temperature, reducing the formation of NOx (nitrogen oxides).
Types of EGR
- Pneumatic EGR: vintage, with vacuum valve
- Electric EGR: modern standard, stepper engine
- High pressure EGR: upstream of the DPF
- Low pressure EGR pressure: downstream of the DPF (cleaner)
Common problems
- Dirtiness: soot + oil creates "sludge" which blocks the valve
- Engine block: EGR forced open = extreme power loss
- Replacement: €300-€800 original spare parts
EGR Off
EGR software removal (edit ECU file to stably close the valve and ignore the sensors) is the most frequent modification in diesel chiptuning. Illegal in Italy for road use. See DPF.
High and low pressure EGR
The high pressure EGR takes the gases upstream of the turbo/DPF and is rapid but tends to get dirty with soot and oil; the low pressure one takes them downstream of the DPF, which are cleaner, and is common on Euro 6 diesels. In both cases the valve is controlled by the ECU based on load, speed and temperature to achieve the balance between NOx and particulates.
Maintenance and diagnosis
The most frequent problem is the encrustation of the valve and the duct, which causes loss of power, smoke and error codes. Cleaning or replacement solves the problem, while software deactivation (EGR off) - a much requested change - is illegal on the road in Italy because it increases NOx beyond the limits. During remapping, however, it must be checked that EGR management remains consistent so as not to trigger reduced mode.
Frequently asked question
"Can I eliminate the EGR to prevent it from getting dirty?": software deactivation is technically possible but, on the road in Italy, it is illegal because it causes NOx to rise above the limits and invalidates the approval. The correct way is to clean or replace the valve and, where applicable, update the manufacturer's software. During legal remapping, EGR management remains active and consistent with the new calibration.