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Catalytic Converter Autolab

January 1, 1970

Check Engine Light Series: Article #3

Did you know there are more than 1,400 reasons that can cause your vehicle’s “Check Engine” or “Service Engine Soon” warning light to turn on?The light is part of your vehicle’s on-board diagnostics (OBD-II) system and can indicate anything from a quick fix like a loose gas cap to a major problem, such as engine misfire.The primary purpose of the OBD-II system is engine management with a secondary focus on emissions reduction. Your car is programmed to alert you any time the engine control computer detects that a sensor or system isn’t performing the way it’s supposed to.Here’s another example of a problem that can trigger the light…

Trouble Code: P0420 Catalyst Efficiency Low (Below Threshold) Bank 1

What is the first thing you think when you discover a stored catalytic converter code, such as a P0420 Catalyst System Efficiency Low Bank 1, in your OBD II equipped vehicle? That the catalytic converter is defective? Codes like this are very common. So are snap judgements. Many times, when a cat efficiency code is stored, the converter is bad. There are also a great many times when snap judgements, or incomplete diagnosis, prove to be incorrect and the converter is not faulty.A good rule to remember is: Just because a part is mentioned in the code description does not mean that it is bad. I appreciate a good auto parts professional and the complementary code retrievals they perform are a real service to the community. However, a code retrieval is not a complete diagnosis. Retrieving stored codes only provides the trained technician with a place to begin a diagnosis.Let’s consider the catalytic converter. The powertrain control module (PCM) depends upon voltage input signals from the upstream and downstream heated oxygen sensors (HO2S) to determine if the catalytic converter is functioning efficiently. The upstream HO2S is positioned before the catalytic converter, between the engine and the converter. The downstream HO2S is after the converter, between the converter and the tailpipe. Because the catalytic converter is designed to decrease exhaust emissions, the upstream HO2S and the downstream HO2S are expected to input very different voltage patterns to the PCM. It is easy to see that if either HO2S is not functioning properly, the PCM could perceive it as catalytic converter inefficiency. It would be terrible to replace an expensive (sometimes thousands of dollars) catalytic converter just because of a bad HO2S or a broken wire.Likewise, a leak in the exhaust system may inadvertently convince the PCM that the catalytic converter is functioning inefficiently. If the upstream HO2S is being fed outside air, the variation between it and the downstream HO2S may not meet minimum allowable parameters. This could tell the PCM that the catalytic converter is functioning inefficiently.Assuming that the catalytic converter has failed; certain other components and/or sensors may have also failed and could be contributing to either a lean exhaust condition or a rich exhaust condition. A rich condition (too much fuel) often contributes to catalytic converter failure. If the converter is replaced without rectifying the rich condition, you can expect repeated catalytic converter failure. This can be very frustrating to a layman, but a professional technician should be able to diagnose it without too much trouble.Catalytic converters, on new vehicles, are typically warrantied by the manufacturer up to 100,000-miles (by federal mandate). The staff at your local, independent auto repair facility can help you with the specifics of your catalytic converter warranty (where applicable).While there are some decent aftermarket catalytic converters available, they usually depend on the vehicle manufacturer and engine size. I have used a certain brand of aftermarket converter that has given good service on every four-cylinder Honda upon which I have installed it. The same brand of converter has failed on every six-cylinder Toyota that I have used them on. To this day, there are certain vehicles upon which I will only use an OEM catalytic converter. Vehicles with a V6 or a V8 engine (or larger) get an OEM replacement catalytic converter in my shop. I have been disappointed by aftermarket converters too many times to take a chance with a loyal customer’s vehicle. The good news is that less than five years ago, all aftermarket catalytic converters were subpar so, they are getting better. Most aftermarket converters are sold with a 5-year/50,000-mile warranty but the warranty is voided if the engine is not functioning properly. At Autolab, when we recommend an OEM converter over an aftermarket, it’s because we want to be able to stand behind it for 3-years and 36,000-miles. We never want to put an inferior part on your vehicle.When should you replace the catalytic converter as a preventative maintenance item? I have seen vehicles with 200,000+miles and a factory converter that was functioning great. I can’t recommend replacing it.What To Do When Your ‘Check Engine’ Light Comes OnWhen your Service Engine Soon light turns on, you won’t know whether it’s because of a P0300 – P0312 or a completely different issue. The first thing we advise is confirming that it is the ‘Service Engine’ or ‘Check Engine’ light. If you’re not sure, consult your owner’s manual.If it is the engine light, see if the gas cap is to blame. Check to make sure the gas cap is tight and that there’s no rust or debris preventing it from sealing. If that all checks out and the light doesn’t turn off within the next several miles, you’ll want to schedule an appointment with Auto Lab for further testing. We’ll be able to retrieve the code(s) and perform pinpoint testing to zero in on the actual culprit. From there, we can provide an accurate cost estimate for the repair.See our detailed guide on how to respond when a dashboard warning light turns on.

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