Rick's Free Auto Repair Advice

What causes catalytic converter to go bad

Catalytic converter problems

What you need to know about catalytic converter problems

If your vehicle displays any of the following trouble codes: P0420, P0421, P0422, P0423, P0424, P0430, P0431, P0432, P0433, P0434, you’re looking at a problem with the catalytic converter. Unfortunately, too many people try fixing catalytic converter problems by replacing it. Bad move. Here’s why; catalytic converter problems are NEVER the cause—they’re the effect. There’s a saying that converters never die, they’re murdered and it’s absolutely true.

Every day I see people going to automotive forums asking about catalytic converter cost. But when I ask them what caused their catalytic converter problems, they act as if these things just wear out. They don’t. Catalytic converter problems can be caused by

Catalytic converter plugged

People think catalytic converters plug up on their own. They don’t. They overheat and the ceramic honeycomb melts and THAT’s what causes the exhaust restrictions.

Overheated catalytic converter

Overheated catalytic converter

Overheating can be caused by any of the following:

Intake manifold air leaks–that creates a lean condition and the computer responds by adding more gas. That extra gas winds up in the converter and causes it to overheat.

Leaking fuel injectors–That dumps fuel into the cylinders and then into the catalytic converter, causing overheating.

Incorrect spark plugs–That cause misfires and the extra gas goes into the catalytic converter

Incorrect ignition timing—You guessed it. That causes misfires

Faulty O2 sensor—bad reading equals bad air/fuel mixture

Impact damage that shatters the ceramic honeycomb and causes the converter to clog

Impact damage that shatters the ceramic honeycomb and causes the converter to clog

Faulty EGR valve—again, bad mixture equals misfire

Oil or antifreeze entering exhaust—Remember that coolant leak you never fixed? Well, where did you think all that extra coolant was going? Coolant and oil are just extra fuel to a catalytic converter and that causes overheating.

Silicone contamination—So you fixed the exhaust manifold gasket yourself and used high temperature RTV silicone, huh? Well guess what? RTV can’t withstand exhaust manifold temps. As it degrades, it goes into the catalytic converter and destroys it.

Teflon tape—replaced an oxygen sensor and thought it would be a good idea to wrap it with Teflon tape? Bad boy. It degrades and destroys the catalytic converter.

Aside from overheating caused by improper air/fuel mixtures, there are only two other things that can result in these trouble codes:

Catalytic converter failure from impact damage

Remember the parking lot curb you ran over? Nice going. It’s going to cost you a new converter.

Defective converter—yes, it does happen. But it’s rare.

So FIX the underlying problem before you even THINK about replacing the catalytic converter or you’ll be replacing the new one.

Want to learn more about catalytic converters? Click here and here.

Diagnose a catalytic converter problem

©, 2013 Rick Muscoplat


Posted on by Rick Muscoplat

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