If your check engine light came on and you got Error Code P0420 (catalyst system efficiency below threshold – bank 1) when you checked it, don’t worry. Although there is probably something wrong with your catalytic converter, you may be able to get it back to normal without having it replaced. Depending on how bad it is, a good catalytic converter cleaner might do the trick. There is also a couple of other ways to clear the code without replacing your converter.
Check the Exhaust System for Leaks
If exhaust is leaking out somewhere before it even passes through the converter, you have a problem. You should make sure that the rest of the exhaust system is operating the way it should. The problem might not even be your cat converter. In order to do this, you can hook a vacuum cleaner up to the tailpipe and duct tape it so that it’s sealed. Then, listen for leaks in the line with a makeshift stethoscope (or a legitimate one if you have it).
Use Catalytic Converter Cleaner to Remove Residue or Build-Up
It could be that your catalytic converter is caked up with gunk and isn’t functioning properly as a result. A formulated catalytic converter cleaner will loosen up and remove any residual build-up that has formed over years of use. There are other ways to clean a catalytic converter, especially if you’re willing to put in the work it would require to remove it and clean it by hand. That might end up being a pretty big job though. To use a catalytic converter cleaner, you simply pour it into your tank with a certain amount of gas left, drive it until empty, and hopefully your converter will be cleaned out after that.
Check Your Oxygen Sensors
In order to check your sensors, connect a volt meter to the feedback wire and ground. Be sure it’s set to millivolt. Start the engine and let it idle for several minutes. After the engine is warmed up, watch the voltmeter closely. It should be centered somewhere around 150 millivolts, but the needle will bounce a bit. Have someone pull the throttle. The needle should go down for less than a second then rise for less than a second. After this, the needle should return to its original position as your vehicle goes back to idle. If not, you may need to fix or replace a sensor.
Is it Really Necessary to Fix this Problem?
The catalytic converter is responsible for reducing smog. If you ignore the P0420 error code and continue to drive your vehicle without fixing the problem you will probably not pass your vehicle emissions test. Your vehicle may also produce thick smog when you drive it. If none of the quick fixes described above work at clearing the code, you will probably need to purchase a new catalytic converter. If so, hiring someone to take care of it for you is a good idea, as replacing it yourself may be a hassle.