Q: o2 sensor problem on 2000 Lexus GS300

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ive got a 2000 lexus gs300 and had code p0141 come up. i replaced the rear o2 and the same day i replaced it the code p0135 came up. is that normal? i have 96000 miles on it. does the back one go out then the front like that so soon?
(1) Answer
Both codes are for the same problem - O2 sensor heater problem. Most likely open/short in heater circuit of heated oxygen sensor, but there is another possibility of ECM problem. It is normal to get another code as they are for the same problem. It means that initialy the problem was not solved as it wasn't the sensor faulty that you replaced initialy. There are 4 sensors in your car and any of them could be faulty. The best solution in this case would be to take your car to the mechanic who knows electronic diagnostics and would be able to test the car and diagnose exactly if it is the computer or the sensor faulty and if it is the sensor, then which one exactly.