Getting to grips with EGR valve’s P0104 Exhaust Gas Recirculation Insufficient Flow fault code.

About Exhaust Gas Recirculation

EGR is an acronym for Exhaust Gas Recirculation, this means the exhaust gases are reintroduced into the vehicles intake. “Why would you want to do something like this?” you might ask. “Especially if your engine combusts diesel, then the soot surely would be forced back into the engine?”.” Correct!” we would reply. However we have a blog on the soot issue.

Using EGR lowers the combustion temperature as these gases have already been used in the combustion stage. They cannot combust again in theory, thus making them inert. This causes a smaller combustion when mixed with “clean” air and fuel in the combustion chamber making a “not as good” burn hence lowing the temperature.

Lowing temperatures stops the production of nitrogen oxides (NOx (x being an unknown quantity)), our poisonous friend, therefore making the air we breathe much safer.

The Repair

On a Volkswagen, Audi Seat or Skoda vehicle the fault code your likely to see with a fault relating to an EGR valve is 16785 rather than P0104 Exhaust Gas Recirculation Insufficient.

This fault code is telling us that the engine ECU has detected the flow of exhaust gases through the valve is too low. This can be caused by number of reasons:

  • A blockage somewhere in the EGR circuit
  • A broken or faulty EGR valve
  • A broken or high resistance in the EGR valve electrical circuit
  • A faulty engine ECU ( Highly unlikely but we have seen this once )

Using the manufacture diagnostic machine it is possible to see problems without intruding on the vehicles mechanical parts. The MAF (Mass Air Flow) Meter was reading incorrectly on a drive for an EGR to be open, for instance.

We proceeded to carry out an electrical circuit test (drop test and load test) for the EGR valve. The result of this was we were able to prove the circuit from the engine ECU up to the EGR valve was working correctly.

The next test for us was to remove the Exhaust Recirculation Valve. This is when we found excessive soot as seen in the picture above. It is completely blocked to the point the valve could no longer open as a conclusion this was the cause of the P0401 Insufficient Flow Detected fault code being generated on our VW Golf.

Carrying out a bypass test eliminated the ECU of any faults relating to the EGR Valve.

Cause and Affect

This scenario can also throw another fault code P0403 Exhaust Gas Recirculation valve malfunction (N18) as the valve is physically stuck, the affect is the engine ECU thinks the EGR motor is faulty or seized. When in true fact its being held against its will by the carbon build-up. Again we would follow a test plan to confirm this to be the case before replacing any component.


Like this topic then maybe you should read Carbon Removal FSI and TFSI Engines

Want to learn more? All training material we use is provided from Volkswagen at a fee head over to Volkswagen Erwin