OBD II Code Questions

[MazdaPU]

I have a 1999 Mazda B2500 with 80K miles. It idles and runs really well. It recently started giving me both P1131 and P1132 codes; H02S bank 1 Sensor 1 A/f too lean and bank 1 sensor 1 A/F too rich. I believe this is the O2 sensor before the catalytic converter. Also P0401 EGR flow insufficient detected which I think may have nothing to do with the others, but not sure.
My question is, how can P1131 and P1132 exist at the same time, is one causing the other? Also, is the problem maybe being caused by something upstream? Any thoughts would be greatly appreciated before I start shotgunning parts in.

 

[simpler=better]

I have a 1999 Mazda B2500 with 80K miles. It idles and runs really well. It recently started giving me both P1131 and P1132 codes; H02S bank 1 Sensor 1 A/f too lean and bank 1 sensor 1 A/F too rich. I believe this is the O2 sensor before the catalytic converter. Also P0401 EGR flow insufficient detected which I think may have nothing to do with the others, but not sure.
My question is, how can P1131 and P1132 exist at the same time, is one causing the other? Also, is the problem maybe being caused by something upstream? Any thoughts would be greatly appreciated before I start shotgunning parts in.

It's probably DPFE related, check that it works (I can't find the link but there are a few writeups on here)

Then clean your injectors (there are a few writeups it's fairly easy to do)

My 2.5 did that when the EGR tube was collapsed and my injectors were stock (with 200k on them)

 

[MazdaPU]

It's probably DPFE related, check that it works (I can't find the link but there are a few writeups on here)

Then clean your injectors (there are a few writeups it's fairly easy to do)

My 2.5 did that when the EGR tube was collapsed and my injectors were stock (with 200k on them)

Thanks! That gives me a starting point.

 

[adsm08]

Yeah, EGR figures into the a/f mix calculations. If the EGR readings are wrong because the sensor is bad it can make it do weird and stupid stuff. Fix your EGR codes first.