My check engine light is on. Code is for cat. I'm trying to find out if the cat is bad or if one of the O2 sensors is bad.
Rear O2 sensor range? on 2002 Toyota Camry
The computer in your car compares the reading between the front and rear Oxygen Sensor to see if the Catalytic Converter is working efficiently. The sensors have a heater element in them to heat the sensor internally, the sensor must be kept at a high temperature to operate correctly, (if the element fails it will set a code related to heater circuit open). A lazy sensor can allow the computer to misinterpret the operating efficiency of the catalytic converter setting a low efficiency code. The sensor output need to be tested using an oscilloscope comparing the front and rear sensor pattern , the front sensor should show activity and the rear sensor pattern should be relatively flat in a properly operating catalytic converter. The catalytic converter should using a non contact thermometer show a temperature difference front to rear of 150 to 200 degrees F at 3000 engine RPM.