Exhaust gas recirculation (EGR)

What it means

The EGR system feeds a measured amount of exhaust gas back into the intake. This lowers the burning temperature and cuts harmful nitrogen oxides. Exhaust is sooty, so the valve and its passages clog with time, most of all on diesels used for short trips.

Codes in this group

Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.

What you may notice

• Rough idle or stalling (valve stuck open)
• Pinging under load (no flow)
• Loss of power and limp mode on diesels
• More smoke

Common causes

Most likely first:

• Carbon build-up blocking the EGR passages
• An EGR valve stuck open or closed with soot
• A failed valve motor or position sensor
• A leaking vacuum hose on vacuum-operated valves
• A blocked EGR cooler

What to check first

• Cars used mostly for short town trips suffer most: a longer run at steady speed helps keep the system cleaner
• A workshop can often clean the valve instead of replacing it

Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.

After the repair

Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.

Related codes

Secondary air injection (P0410), Catalytic converter efficiency (P0420), Fuel vapour (EVAP) system (P0440), Diesel particulate filter (DPF) (P2002), Diesel exhaust fluid (AdBlue) and SCR system (P203F). All codes.

Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.