Can you tell me what these four codes mean? po401 &402, po171, po1131. Thanks!!

Question

What could the problem be??

Answer 1

P0401 Exhaust Gas recirculation flow insufficient detected

P0402 Exhaust gas recirculation flow excessive flow detected

P1131 -02 sensor not switching

P0171 Fuel trim lean too lean.

Over all this is a lean condition Something is causing the EGR to not open , there is where you get P0401, Then if it does open it excessive this is where you get a lean bank condition , the 02 sensor not switching and and a lean fuel trim. Check the vacuum connection especially for the EGR, incorrect vacuum lines being connected   can also be the cause of the whole condition. The only way you can have a EGR that is excessive and insufficient at the same time is a faulty EGR solenoid.