What does the 'egr flow malfunction' P0400 and 'O2 Sensor circuit malfunction' P0150 mean on a 1996 Nissan Maxima?

Answer 1

po400 means you have insufficient or excessive exhaust flow within the egr system. The o2 code means it has detected this as well. Chances are both are on because either the egr system is not passing exhaust fumes into the manifolds properly. or the manifold has a leak. You can start by checking the manifold for leaks, cracks, holes, etc. If the manifolds seem tight, try actuating the egr valve. If the egr valve works blow compressed air through the tubes of the egr system and find the leak or clog. Carbon buildup is the number one cause for a clogged egr. Also check the lines make sure they are free of holes and are attached. Dont buy a new o2 sensor until you have fixed the egr code as the egr malfunction will likely set the o2 code again within a few months. hope this helps..