Contour Enthusiasts Group Archives Forums General Troubleshooting O2S bad. Need location!

Hello All! I have a 99 Contour 2.5 V6. CEL came on, engine seems to be running normal. Brought the car to autozone. Diagnostics show that Bank 1 O2S is bad. Now I am trying to figure out which one this is referencing. From what I understand bank 1 is the left side of the engine (front of car?)but then I see 2 O2 sensors. I'm guessing the up and downstream.. How do I know which one needs replacing???

Thank You!
FEDFIREGUY

Welcome. Post the exact code (it could be something else besides the O2 sensors). There are two Bank 1 (firewall side) sensors upper (11) and lower (12).

The other two are at the radiator side Bank 2 Upper (21) and Lower (22).

Bank 1 is right side of the engine (which is firewall side). Bank 2 is left side of the engine (radiator side). The front of the engine is on the right (passenger side) of the vehicle for our transverse mounted engines.

any recommendations for how to get in to replace Bank 1 Sensor 1 back there near the firewall...

have read all postings on 02 sensors, EGR problems on the forum. Have had similar issue: error codes of faulty EGR DPFE, insufficient switching control valve/lean. Tuned up, replaced DPFE. CEL off for a while, now back on. Replaced Bank 1 sensor 2 (easy one). Think I need to replace bank 1 sensor 1 and clean EGR passages. thoughts?

many thanks
matt

98 SE 5-spd, 93k

many thanks for the help. got the job done last weekend, though that was one helluva pain in the butt. still not sure how I got the wrench on it. Good news is that CEL is gone finally (6 weeks) after replacing all of the 02 sensors, DPFE, and plugs. Still saved a bundle compared to what my local Ford dealer wanted for doing less work.