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Bad Catalytic Converter?

Toyota says the code is P0420 and the Catalytic Converter is rattling under heavy acceleration showing the Catalytic converter is bad and should be replaced. Toyota wants 2,334.00 which seems very high to me. Is it the Catalytic converter? Should I look for someone with a lower price to replace it?
The car is a 2004 Toyota Prius.

In my opinion you should first get the diagnosis of bad cat confirmed, for a couple reasons. The rattling, could just be a rusted loose heat shield somewhere on the exhaust. And the P0420 could be an old slow reacting downstream O2 sensor, or even an exhaust leak. Search this and other forums on the P0420 code and you will find many people (including myself), did not need a new cat, only a new sensor.

Is the DEALER the best shop for exhaust repair? What is price of part vs install cost? 1855 for part and 466 for install or don’t they break down repair cost?

The problem with the Prius, few independent shops are comfortable working on them…How many miles on your car? An independent muffler shop can probably replace your CAT for 3 or 4 hundred dollars with an aftermarket part but that might not cure your problem…

What is the best way to get a confirmation the catalytic converter is the problem instead of an O2 sensor? The dealer did not break down the price of the part versus the installation fee.

To determine if it’s a catalytic converter problem or an O2 sensor problem, you connect a scanner capable of reading real-time diagnostics. Then look at the signals from the O2 sensors. The front O2 sensor should read a rapid voltage change from .40-.80 VDC. The O2 sensor after the cat should have a voltage reading that floats between .70-.90 VDC.

If the O2 sensor after the cat voltage starts jumping between .60-.90 VDC, and there’s no O2 sensor code, there’s a problem with the catalytic converter.


In theory, Tester is right. But there are conditions where the O2 sensor can be working within its limits, enough so that it doesn’t trip a DTC for the sensor, but still can trip the DTC for the cat. A mechanic that is familiar with how the sensors work should be able to tell when it is the cat and when it is the sensor, problem is that not all mechanics can tell the difference, and those that can do not always work at a dealership.

Toyota’s are the worse for this, especially the ones of your era. Something in the PCM programming makes them more sensitive to the P0420 code that they should be. Heres the kicker, your dealer should have known this and reprogrammed your PCM first, but many do not or will not do this. Why give it away when you make a couple grand off it.

My thanks to everybody for all of the help. I will look for a good mechanic to get a solid diagnosis on the converter.
Thanks again…

Good Luck Lou…But much of the Prius computer controls and diagnostics are proprietary and few places outside dealerships can effectively work on them. You might check the Prius forum, sponsored by Toyota, for more information…

How many miles on your Prius? Is it still covered under warranty?

So how much does it cost to re-program the computer? My 2002 has the intermittent 0420 and I got the impression they want to put in a new computer for a very large amount of money.

I would expect to pay no more than 1 hour labor for a reflash

Should one expect the Toyota dealer to flash the memory? I got the impression from things others have said that Toyota wants you to pay for a new computer. As long as I can muddle through I don’t want to pay them for a new computer because THEY would prefer the money.