Though GM cars as a whole are no more likely than any other brand to experience catalytic converter failure, the company has recently begun hearing complaints of premature converter failure on some 2001 and 2002 Impala, Monte Carlo, Buick Regal and Grand Prix cars (W-Platform). This failure causes poor fuel economy, engine overheating and power loss above 35 mph. Perhaps worse than the converter failure itself is the sensor failure that sometimes tricks the computer into believing all is well.
A catalytic is a small box installed into the exhaust pipes of all modern gasoline engines. This device uses the wasted energy of passing exhaust gases to super-heat a carbon-metallic matrix to temperatures approaching or exceeding 1000 degrees Fahrenheit, which then interacts with subsequent gases to convert their most harmful components into more inert forms before release into the atmosphere.
All catalytic converters have a few common weaknesses. The first is contamination, which is a condition wherein some foreign element (like lead) is ingested by the engine, burned and deposited on the converter matrix. These deposits will build over time, clogging the converter and rendering it useless. The cat's second greatest enemy is heat. Whereas these units are designed to operate at temperatures that would soften steel, they can only withstand so much. When modern converters overheat, the matrix begins to crack and melt under the strain, destroying the converter.
The converters used in the aforementioned GM cars have notoriously thin end-cone pieces, which can break and lodge in the matrix. Once this happens, the engine begins to build-up back pressure, trapping excess heat in the converter housing instead of expelling it. This condition can rapidly lead to converter meltdown and failure.
According to a letter issued by GM to customers on automotiveforums.com, these cars often experience a failure to illuminate the dashboard malfunction lamp after converter melt-down. This can lead to serious problems where engine longevity is concerned, since excess back-pressure can lead to engine overheating and valve damage.
Per an excerpt from GM's standard powertrain warranty contract for the W platform cars: "For eight years or 80,000 miles, whichever comes first, if the catalytic converter or vehicle (powertrian) control module is found to be defective, GM will repair or replace it under the Federal Emission Control Warranty."
Provided your car is within these ranges, GM must repair your car to maintain emissions compliance. If you are past eight years or 80K, repair costs run between $200 for a generic converter to $1100 for a GM replacement. A tip for working with your mechanic: clogged catalytic converters are not considered a hazardous substance by law, and it costs nothing to simply throw one in a dumpster. Don't fall for the "disposal fee" line.
