oxygen sensor pre catalytic converter on 2000 Lexus ES300

I have 165000 miles on my car .The OBD sensor shows pre cat converter malfunction.I changed it and used a Bosch one .Still the same diagnostic codes.Is the catalytic converter bad.Had it checked by a mechanic and he thought that it may be bad.Nervous about buying another as they are expensive before checking one

by in Dayton, OH on September 11, 2009
4 answers 1 comment
ANSWER by on September 11, 2009
Yes, the Catalytic Converter is defective. Many folks, even full time techs confuse the Converter Codes. See this article that I wrote on CAT codes. www.RepairPal.com/OBD-Code-P0420. It applies to either a 'warm up' or main Catalytic Converter 'below threshold' code malfunction.
ANSWER by on April 19, 2010
I have a 2000 lexus ES300 with 14700 miles on it. The A.T. U140E transmission failed completely. A pin on the front planetary broke, allowing the transmission shaft to go backwards and tear up the rear planetary. Doing some research, I've found that this was not unusual and Lexus changed during 2000. True??
ANSWER by on September 29, 2010
I have 69,000 origanal miles and catalytic converter is going out. Is that normal
COMMENT by on October 01, 2010
Lexus and Toyota has had to extend their CAT Converter warranties to 8 years or 80,000 miles because they are having problems with their CAT Converters. Call the Dealership and ask a Service Writer to check your VIN code for this issue, if you fall within the 8yr/80k window, you should be 'good to go'.
ANSWER by on January 25, 2011
Not sure what an obd sensor is but I will assume you mean that you replaced the air/fuel rato sensor. Cat codes usually mean the cat is bad or rear O2 sensor which monitors the cat. Your scan tool can verify sensor voltage, if your rear sensor follows the front sensor your cat is bad. If your rear sensor does not respond to artificial stimulation or its rise time is to slow, then you may need a rar O2 sensor