Lets start with the P0401, which could be the cause of the O2 sensor fault or it could be 2 problems but definitely both are affecting the mileage and performance.
1. Check all EGR system vacuum hoses. Replace as necessary. Access ECM behind bottom center of instrument panel, in front of console. Ensure ignition is off. Disconnect ECM E4 connector. Turn ignition on. Connect a jumper wire between ground and terminal No. 23 (Black/White wire) at ECM E4 connector.
2. With jumper wire connected, Vacuum Switching Valve (VSV) is on. Apply air pressure to VSV port "E". Air from port "E" should flow through filter on end of valve. See Fig. 4. Disconnect jumper wire. Air from port "E" should flow from port "G". If valve operates as specified, go to step 6). If valve does not operate as specified, go to next step.
3. Turn ignition off. Remove EGR VSV. Using ohmmeter, measure resistance between valve terminals. Resistance should be 33-39 ohms at 68 F (20 C). Check for continuity between each terminal and body of valve. If continuity exists, replace VSV. If continuity does not exist, go to next step.
4. Check VSV operation. Apply battery voltage to valve terminals. Apply air pressure to VSV port "E". Air from port "E" should flow from small filter on end of valve. See Fig. 4. Remove battery voltage from valve terminals. Air from port "E" should flow from port "G". Replace VSV as necessary.
5. Check for an open or short in wiring harness between instrument panel fuse block and ECM. Repair wiring as necessary.
6. Check EGR vacuum modulator. Replace as necessary. If EGR vacuum modulator is okay, check EGR valve. Replace as necessary. If EGR valve is okay, go to next step.
7. Check Manifold Absolute Pressure (MAP) sensor. Replace MAP sensor as necessary. If MAP sensor is okay, replace ECM and retest.
Thursday, February 7th, 2013 AT 5:56 PM