Is something wrong here?

[kimiraikkonen]

Should both downstream (post-cat) O2 sensors be roughly the same value (Bank 1 vs. Bank 2)?

The below picture was taken at idle.

• Bank 1 post cat sensor (B1S2) shows 0.710V
• Bank 2 post cat sensor (B2S2) shows 0.140V

I assume both Bank 1 and Bank 2 should be close to each other and not that divergent on the post-cat. Any thoughts on why this is the case?

The pre-cat sensors (S1) seem to be switching fine when revving the car. No codes showing but trying to see if I have an exhaust leak or need to just replace the O2 sensor.

[330ciprem]

Looks like a lazy O2 sensor.

Maybe swap them and check what readings are you getting?

[kimiraikkonen]

Originally Posted by 330ciprem

Looks like a lazy O2 sensor.

Maybe swap them and check what readings are you getting?

Thanks for the feedback. I hit 120K mi recently and had replaced the front O2 ~90K mi.....and am thinking to do the rear O2s now to see if this makes a difference.

Other than that, any thoughts on why the low voltage on rear Bank 2 sensor? I monitored it today while driving and the Bank 2 does increase voltage under engine load (creeps up to 0.5 to 0.6 V), but once back at idle it quickly drifts back down to the 0.1V range. No ECU or OBD codes, so am assuming the Cat is still working fine.

Am worried this is either a leaky injector or compression issue?

[sibhusz06]

O2 readings around 0.1-0.3v indicates a lean condition, whereas 0.5 is about normal, and 0.7 and above indicates a rich condition. Most O2 sensors start reading lower as they age which eventually causes your engine to run rich and waste fuel. I don't know if they foxwell indicates the injector width but if they are all equal for the bank in question, im guessing your O2 sensor is going bad or just worn..

[kimiraikkonen]

Originally Posted by sibhusz06

O2 readings around 0.1-0.3v indicates a lean condition, whereas 0.5 is about normal, and 0.7 and above indicates a rich condition. Most O2 sensors start reading lower as they age which eventually causes your engine to run rich and waste fuel. I don't know if they foxwell indicates the injector width but if they are all equal for the bank in question, im guessing your O2 sensor is going bad or just worn..

Thanks for the feedback. Am leaning towards a worn rear O2 sensor and plan to replace them shortly. Will let you know if that changes the O2 voltage readings.

[gmdoctor]

isn't the rear o2 only there to monitor catalyst efficiency? if no engine light just leave it alone. it shouldn't change the way fuel is trimmed.

[ItsGary]

Originally Posted by gmdoctor

isn't the rear o2 only there to monitor catalyst efficiency? if no engine light just leave it alone. it shouldn't change the way fuel is trimmed.

PreCAT does AFR adjustments
PostCAT is for monitoring, basically emissions checks Post CAT