Hi, I just has an independent do 90K maintenance on my RX300 2000. He didn't even touch the O2 sensors or anything close to them but they both came up bad immediately after the job. Same thing happened to a friend. What gives? Second question is what happens if I continue operating the vehicle with the check engine lit (presumably due to bad O2 sensors)?

 

are you sure its o2 sensors or the airfuel ratio sensors? did you get ob2 reader and read codes? thanks

 

I think he might be referring to the A/F (air fuel sensors). If you get this code, it can cause a slightly more than normal increase in fuel consumption. I'd confirm what code it was.

 

The guy that read the code said both O2 sensors. I'll get the codes again. The question remains; with a bad O2 sensor, does the computer default to a "no sensor" setting or what? Does that result in bad mileage, carbon buildup,engine malfunction?
JC

 

Yes, there is a default. You can still run, but you run a lot more gas.

 

I changed out the front brake pads, started the car up, CEL came on. I thought for sure it was the ABS system. Pulled the codes, O2 sensor.

 

I'd need to know the actual code.

 

rear O2 sensor, already replaced.

 

Here's the codes that came up for my vehicle after the 90K service:
P1346 VVT SENSOR CKT BNK #1 RANGE FAULT
P1351 VVT SENSOR CKT BNK #2 RANGE FAULT

 

By The Way, I've Been Driving For About A Month After The Service And The Mileage Hasn't Changed; Still Steady Around 17 Gpm.

 

That is your variable valve timing sensors.17 is all you normally get?

 

Your sensors should be fine, but the problem here is that you have a problem physically with the timing belt, it's either stretched from use and/or it's skipping teeth on the timing belt. I'd reset the code and see if it comes up again, but I'd also ask as to when the timing belt was last changed. In addition, I can add that hot temperatures CAN, though not likely, on occasion cause this particular issue. I had relatives in northern Mexico who were also mechanics and would get this issue, where the temperatures are much hotter than say Mexico City or even now where I live in Florida. However, this occurred with much older vehicles than I was talking here.

If code still pops up, then you need to have some examine the timing belt itself.

There is another set of codes, 1345 and 1350 that are related to VVT sensors being bad, but this would not be the case with the codes you pulled up.

 

Timing belt replacement was one of the jobs for the 90K service. Maybe the independent put it in wrong. I guess I should have it reinstalled.

 

Briefly after the 60K service I averaged 18.2 mpg but its been 17 for most of the intervening 30K miles. I drive small towns, rural & mountain; Only about 20 % highway driving. What's a reasonable mileage under those circumstances?

 

Depends on your driving habits, but even if you have some hills in the way, it can knock you to the mpg you have.