So every month or two I get this guy...

2 Faults Found:
16523 - Oxygen (Lambda) Sensor B1 S2
P0139 - 001 - Response too Slow - Intermittent
17584 - Bank1: O2 (Lambda) Correction Behind Catalyst
P1176 - 001 - Control Limit Reached - MIL ON

Not sure if it's a bad sensor, or if it's a bit lean. We put the water meth on when the 02's were replaced, about a year ago, so not really sure.

I added a bit more fuel to the tune since it's 90 degrees this week...