The check engine light came on, it was the o2 sensor upstream, I had it replaced with a Denson, my fuel economy has dipped to below what it was a a faulty sensor! Normally my mpg is between 28 and 29, now it's 23. Any ideas?

 

By the way its a 2010 rx450h with 174,500 miles.

 

I assume you mean Denso not Denson. There is little chance that an O2 sensor would have that effect on your MPG. Possible, but unlikely.

 

This sensor is also fuel, as soon as the check light came on my mpg dropped below 25. And yes denso

 

Have you checked the wheel bearings and brake calipers for sticking? Very probable cause for a drop like that, at that mileage. I would suspect that near the top of the differential diagnosis list.

 

Keep in mind this sensor impacts the calculation of mpg. You may be getting wrong calculated value before/after. Just use the MPG as an indicator and do actual milage with actual fuel pumped in at fillup.

OMG ... actual milage is yet based on rotation of tire and not actual miles driven & actual gas consumed is yet another estimate.

Salim