Issue 14: Clogging in EGR valves

EGR valves explained

The EGR (Exhaust Gas Recirculation) valve is a component used to reduce harmful NOx gases in the exhaust by reducing the combustion temperature in the cylinders. This is done by recirculating oxygen deprived exhaust gas back into the engine under certain driving conditions.

Causes of EGR valve clogging

EGR valves can be electronically or vacuum controlled. Both are susceptible to sticking or not seating properly due to a build-up of soot, carbon and even oil around the spool or valve seat. This can be caused by underlying engine issues which can prematurely clog up the EGR valve, causing the EML (Engine Management Light) to illuminate and EGR fault codes to be stored in the ECU (Electronic Control Unit).

EGR valve - EGR system

When soot and carbon deposits build up around the valve seat, the valve is not able to fully close. As a result, when in its rest position, the EGR valve allows the flow of exhaust gas back into the cylinders when it’s not required.

More and more EGR valves now have integral position sensors which send valve position information to the ECU. If an unexpected valve position is registered due to it not seating properly, the engine management light will illuminate.

What to do when the EGR valve clogs?

Simply replacing an EGR valve that is clogged will only rectify the problem short term and will inevitably clog up again over time, resulting in repeat customer returns and the possibility of false warranty claims.

Soot build-up

If a valve is clogging up over a short period of time thus preventing proper seating or sticking, the reason for this needs to be identified so that the cause can be repaired before replacement of the EGR valve:

  • Engine issues such as worn or broken piston rings or leaky turbo seals can allow oil into the intake system
  • Rich running engines due to MAF faults
  • Faulty injectors or lazy lambda sensors

These can all be reasons for sooty and oily deposits that will cause the EGR valve to clog up and stick.

If an EGR valve is clogged up, it’s also worth considering that the intake manifold could also be clogged, limiting the flow of exhaust gas through the EGR port to trigger a fault code.

Therefore all associated components need to be inspected before replacement. Some applications require EGR adaption with suitable diagnostic software. Please consult a workshop manual to check if this is the case.

Cambiare Tips and Tricks Issue 14