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Discussion Starter · #1 ·
Hello. '13 LTZ 81k.

Have a few questions regarding 02 sensors post cat.

1. How close in MV should they be to each other? I would think they would be exactly on or very close? But that's usually not the case, they're usually about 30mv apart, with bank 2 being higher. When this happens Bank 2 also will have very high long term fuel trim 15% or higher. I'm not sure if the sensor is just picking up the difference in fuel trim or that 30mv difference is what's causing the problem (high fuel trims) I hope this makes sense? I guess what I'm asking is how much does the computer use post cat 02 sensor data to calculate fuel trim?

2. Someone suggested I may have an exhaust leak. Both mufflers will leak water, not sure if that's normal or if that could be causing a problem? I can see where the leak is so could I get some exhaust epoxy and patch it? And could that be causing any of the trim issues?

3. I know the voltage on the 02 sensors post cat aren't supposed to jump around but as the cat changes temperature wouldn't the voltage change? ie. it would be different on a cold start as opposed to normal operating temperature?

Thanks guys! I really appreciate all the help! It sucks that the only Chevy dealer around here is SO bad both with customer service and shoty repairs, and the GMC dealership officially can't or won't do warranty work on chevys anymore. The only truly good trustworthy honest independent mechanic in this town who knew his stuff died recently. So these forums are a real life saver!!
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