Hey Guys! I am new here on the forum. Having an issue with my Audi A4 1999 2.8 Quattro that simply didn't start in the morning about a week ago. The engine cranks but doesn't want to run. I have check fuel system - there is sufficient gas pressure and the pump seems to work normally. Ignition system also works well - I can get a decent spark. There is one check engine code which is P0411 "Secondary Air Injection System Incorrect Flow Detected". Any ideas why it might not start? Many thanks in advance!

 

The code you have might suggest one of either of your 02 sensors. They are finicky.

2nd suggestion would be the coolant temp sensor, which is a common failure and causes crank-no-starts.

Lastly, it could be a Crankshaft Position Sensor (aka engine speed sensor), which causes your issues.


Honestly I would try the coolant temp sensor first.

 

Thank you very much! The issue was with spark plugs! P0411 appeared to be a separate issue that I am dealing with right now.