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Is a new Catalytic Converter necessary?

I have a 2002 Ford Focus ZX3 with 113,000 carefree miles on it. Over a year ago, my check engine light started coming on intermittently. I had my regular mechanic, and two auxiliary mechanics read the code. All declared I needed a new converter. My regular mechanic told me that I should just wait until I started having performance issues. I have not noticed any loss of power, or decrease in gas mileage, etc, over the last year and the light has been solid almost as long. Should I just continue to drive and or am I damaging my car by waiting?

What really needs to be known are the actual codes. O2 sensor and converter codes can and are frequently misinterpreted. It’s quite possible for something else to cause a converter code.

I don’t know the code, although I suppose I could take my car to a fourth mechanic and get it. I did bring it in last week to the muffler guys (they had quoted me the best price for the new converter) and they assured me it was the converter, and that my O2 sensors were OK.

Many auto parts places will read the code for free, autozone etc. It may be the converter is bad but often there is a preexisting condition that leads to the failure, and you need to be sure that is not the case.

What would be a preexisting condition that could cause the converter to fail?

Stolen info "http://www.catalyticconverter.org/failure/index.htm"
Thermal failure is most often caused when excessive raw fuel comes into contact with the catalyst, and “burns” in the converter instead of in the engine. The high quantity of fuel generates temperatures well in excess of the capacity of the converter, causing meltdown of the ceramic monolith. The melted ceramic could block the exhaust path, leading to a significant loss of engine power. Visible symptoms include heat-related discoloration of the converter shell.

Potential causes of thermal failure include: misfire, malfunctioning oxygen sensor, fuel delivery issue, improper choke setting/operation, and ECU malfunction.
A plugged or contaminated substrate can be the result of an overly rich air/fuel mixture, radiator sealant, and oil or antifreeze entering the exhaust flow. The resultant carbon deposits restrict the operation - and ultimately the flow characteristics - of the converter by coating the unit’s reactive surface. This degrades the converter’s ability to perform its chemical conversion process, leading to potentially illegal levels of HC, CO, and NOx.

Root causes of this problem are a malfunctioning O2 sensor, plugged or inoperable fuel injectors, piston blow-by, leaking head gasket, broken or frozen choke or carburetor float, excessive cranking time, and repeated incidences of running out of gas.

Thermal shock occurs when a fully heated converter suddenly is “cold-quenched,” such as coming into contact with snqw or ice. This leads to sudden contraction of the converter housing, which can cause cracks and disintegration of the ceramic substrate. Symptoms include a "rattling’’ sound when the converter is tapped with a fist or mallet (monolith-type converters only).

Physical damage, caused by running over road debris, collisions and other impacts, is usually easy to diagnose. This type of damage can break up the ceramic substrate or cause restriction that changes the flow characteristics of the converter or impacts the efficiency of the catalyst.

“Converter efficiency below threshold”…Right? But it’s the rear oxygen sensor that’s generating this code, not the converter…My Vic did this, I replaced the rear sensors. I reset the light and it has stayed out. Oxygen sensors have a design life of about 100K miles…

If you do not need to pass an emissions test, you can continue to drive without hurting anything…

For $30 or so you can buy an OBD to USB hook-up cable and a simple program to run on your laptop and you can monitor, read and reset your ECM. Very handy.

If the muffler shop folks are sure it is the converter, they may see discolored metal that tells them that this converter has been red hot - or they may just be in the business of selling converters…

As Waterboy explained, if the converter has overheated, there is another problem that must be addressed before you replace the converter or you will simply cook the new one.

On the other hand, if the code is a “low catalyst efficiency” code, it is likely that the only problem is oxygen sensors that are getting old and slow to respond. With OBD2, your oxygen sensors may still be putting out the correct max and min voltage, but their response time gets slow with age, and the computer interprets this as an inefficient catalyst.