1999 turbodiesel code P0400
 

P0400 code came on, (EGR Flow).
I'm wondering if I may have a vacuum leak somewhere because when I turn the heater on and select air flow to the floor the flap doors do not open to direct air to the floor.
What should I be looking for to find what it causing the P0400 code and how to fix it?

Thanks,
Rick

The EGR vacuum transducer is on the left side. The hose runs over to the manifold to operate the EGR valve. There is no direct measurement of EGR action (as in an electrical sensor on the valve), they measure the difference from the mass airflow sensor to determine if the EGR operated as commanded. If it does not see the expected change in flow then it throws the P0400.

I would check for vacuum leaks like you suspect. The climate dampers on the W210 are vacuum operated.

You can also try swapping the EGR vacuum transducer with the wastegate transducer on the other side temporarily to see if that’s your problem.

Problem Solved!
The hose going to the transducer was off, pushed it back on, cleared the code and all is well.easiest fix ever on this car!