What does that mean?
P0420 is one of the more common trouble codes that we see. Other popular codes include P0171, P0300, P0455, P0442, etc.
The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it’s job is very different from that of a muffler. A catalytic converter’s job is to reduce emissions from the exhaust.
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. Oxygen sensors are also referred to as O2 sensors.
This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a “wear” type item, that is they are not designed to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail. This is what a P0420 means in simplified terms.
Possible Causes
- Faulty Three-way Catalyst Converter Bank 1
- Exhaust Tube
- Intake Air Leaks
- Faulty Oxygen (O2) Sensor
- Faulty Fuel injector(s)
- Leaking Fuel Injector (s)
- Faulty Spark plugs
- Improper Ignition Timing
- Faulty Engine Control Module (ECM)
- Dirty Air Filter
Symptoms so why should I fix it?
Great question! A P0420 code will cause no symptoms aside from the MIL (malfunction indicator light) will illuminate. The reality is there is still something wrong and your car needs attention in order to be in excellent running condition. A poorly maintained car will run less efficiently, burn more gas, and cost you more money in the long run.
Plus, if your check engine light is on for a P0420 code and you decide not to fix it, another more serious code could be triggered and you’d never know. The MIL lights up whether you have one code or ten! While I have your attention, don’t forget to do oil changes as the owner’s manual schedules and keep those tires inflated to the proper PSI.
P0420 HONDA Diagnose things
The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those symptoms are there, the converter likely needs replacement. Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc.
If all that checks out, you’ll want to check the operation of the O2 sensor. To do that, you’ll need access to a scan tool or oscilloscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced.
A few additional DIY friendly tips include:
- Try CataClean, a gas tank additive
- Run 1 gallon of lacquer thinner through the gas tank (when at 1/2 tank) as per Scotty Kilmer
- If you have a heat temperature infrared “gun”, check the exhaust temperature before the cat and right after. The temperature at the exit should be in the neighborhood of 100 degrees Fahrenheit hotter when the engine is fully warmed up and you have the engine running at about 2,500 rpm. Don’t accidentally take the temperature of heat shields, pipe only.
Read Also P0300 GMC Fault Code Problem Solution
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