2004 Toyota Camry in need of Catalytic Converter??

Hi All, I need advice ASAP!!.Someone, please help. I have a 2004 Toyota Camry, LE,

4 cylinder.It has excessive miles on it due to commuting from New Hampshire into Boston, Mass. daily.( I believe 128,000 miles currently) Approximately 6-8 weeks after purchasing my vehicle, it started acting strangely.I was told by the dealership that it needed an O2 sensor. They jerked me around several times, and it actually needed a catalytic converter in addition to the O2 sensor. It was under warranty, so no big deal. The other evening, when traveling back from Rhode Island after visiting family, the check engine light came on. I made it home safely, and first thing Monday morning I phoned the Toyota dealership to have the car diagnosed. It spit out P0420 as the code. Prior to this writing, I read the thread from snipped-for-privacy@yahoo.com, and saw he also had the same code spit out, which is what prompted me to write to you. I was all set to go the dealership and have the vehicle repaired but now I am questioning because of the topic that was brought up about it could be the sensor or the Catalytic Converter. I really dont want to spend 700.00 if I do not have to. How do I know that it is not the sensor?? What if it is and giving a false reading?? What should I do?? Please, any info you could give me would be greatly appreciated. Thanks, Susan.

When the check engine light is steadily illuminated, it means that there is a problem with the vehicle's emission system and there is little or no danger that you will be stranded. In most cases, you will not notice any difference in drivability. If the check engine light is blinking, then you need to pull over, turn the engine off, and get the car towed to a repair facility.

Your car has 2 O2 sensors. Sensor #1 measures the oxygen content in the exhaust gas, and under most conditions, it sends a signal to the vehicle's computer (electronic control module, or ECM) and the ECM adjusts the amount of fuel to be injected. When the sensor is doing this, the constant adjustment makes the signal look kind of like a heartbeat on an EKG monitor. After the exhaust gas passes sensor #1, it passes through the catalytic converter, or cat, where most of the harmful stuff is catalyzed and burned off and cleaned up. The cleaned-up exhaust exits the cat and moves past Sensor #2. If the exhaust has been properly cleaned up, the signal from Sensor #2 should be flatter than the signal from Sensor #1. If the signal from Sensor #2 looks like the signal from Sensor #1, the ECM thinks that the cat isn't working, stores trouble code P0420, and turns on the check engine light.

There is a slight chance that the signal from Sensor #1 is weak and so it looks like the signal from Sensor #2. The signals from Sensor #1 and Sensor #2 can be measured and checked with a higher end scan tool or a volt meter, but if they check out OK, then the cat needs replacement.

Cat failure can result from many cold starts where the engine and cat do not have a chance to heat up and burn off the deposits that form inside the cat; from leaded or cheap gas; and from using too many fuel additives. By any chance, do you routinely add dry gas or anything else to the fuel tank?