All (4) O2 sensors replaced. Still have check engine light

Like the title sais^^^^^^^^^^^^^

Codes P0031 & P0051

I have also checked and its the A/F heater relay and its good.. Any suggestions?

 

No one?

 

fuses?

 

I'm sure you did but I'll ask anyway; you disconnected the battery to reset the codes?

Check fuses.

Check the wiring running to the sensors that an animal hasn't eaten your wiring for dinner.

Check for pinched or burned wiring especially around the EGR Valve or anywhere that gets hot.

Check ground wires that connect to frame.

 

This is exactly what I was going to say. According to my diagnostic flow chart, the only things that can cause these codes are bad wiring, bad o2 sensors, bad relay, or bad pcm. Since you've already replaced the o2 sensors and tested the relay, we know that's not the problem, so I'm guessing at a bad wire somewhere, cause I don't even want to think that it's the pcm. If you need help with the wiring diagrams or connector end diagrams let me know.

 

Pretty much have done all mentioned above . As far as fuses are their any for these besides the relay?

 

Have you actually ohm checked all the wires related to the o2 sensor system with a digital multimeter? Just because you inspected the wiring visually does not mean its not messed up somewhere inside that you can't physically see. I'll find a wiring diagram for you and post it up, maybe that can help you diagnose it a little better.