Recently had my front bumper replaced on my 2000 RX300, and upon receipt of car from mechanic now had a noisy muffler leak along with illuminated "check engine" light. Leak was then repaired (gasket in front of muffler), and light stayed on. Mechanic then did computer evaluation, and said that no error codes came up, and reset check engine light. Light remained off for two days, but is now back on again.
All sensors (o2 & airmix) were replaced 11 months ago when check engine light last came on, and its been good until now..
I should also note that I have noticed lowered gas mileage recently.
Any recommendations as to what might be wrong, especially since computer diagnostics don't reveal any error codes?
Thanx in advance

 

Try checking the codes again, you can go to Auto Zone as well if you don't want to go to your mechanic, they will check the codes for free. What brand were the replacement sensors?

 

haven't any idea what brand sensors were put in: don't even know if my mechanic would remember. Probably some aftermarket variety, but I'm not sure. I'll try too find a nearby AutoZone, and follow up from there.

 

Thanx for Autozone recommendation. They did diagnostic check & found code PO136: Heated O2 sensor HO2S12. Bank 1 Sensor 2.
Not sure why my mechanic told me that he found no problem when he did diagnostic check. Looks like I may need a new mechanic! (or maybe he needs a new computer diagnostic checker).
The printout from Autozone states as one of probable causes "Air/Fuel ratio concern". Could this be from an also malfunctioning airmix sensor, even though a code for that sensor did not come up on the printout?
Thanx again

 

I believe the problem here is that the mechanic knows that he used an aftermarket sensor (*cough cough BOSCH cough*) which doesn't comply too well with the toyota ecu, and made you pay the price for a oem sensor.
Since you say that he replaced all sensors, go to your mechanic and ask him which banks he replaced, but don't tell him which sensor has the error. Then ask him what brand he used?

 

And if he tells you he didn't use aftermarket.... ask him again.

 

Thanks. Shall do!

 

I know it sounds silly but I fixed by replacing the fuel tank cap. Lots of luck. Carl