P0420 TOYOTA – Catalyst System Efficiency Below Threshold Bank 1
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Error code P0420 – or Catalyst System Efficiency Below Threshold (Bank 1) – is one of several trouble codes that fall into the general exhaust system code block.
All P042X codes (where “X” can be any number) refer to the catalytic converter and exhaust system. P0420 refers to the catalytic converter or – more specifically – the oxygen (O2) sensors before and after it on the bank 1 side of the exhaust system.
However, if the P0420 code is the only trouble code – or if the other codes are all P042X codes – the likelihood of a failed catalytic converter is much higher.
What does that P0420 mean?
This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Chevrolet, Ford, Honda, GMC, Subaru, VW, etc.
P0420 is one of the more common trouble codes that we see. Other popular codes include P0171, P0300, P0455, P0442, etc. So be sure to bookmark this site for future reference!
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.
Understanding P0420s
Before the catalytic converter, the oxygen sensor’s voltage will zigzag up and down when graphed. To the contrary, the air-fuel sensor will be at a stable voltage. The post-cat oxygen sensor will be a straight line of voltage if the catalytic converter is good in most cases.
Post-cat oxygen sensors, when good, are at a steady voltage, usually between 500 to 700 mV. If it zigzags, mirroring the pre-cat oxygen sensor, the catalytic converter is highly suspect. Sometimes the post-cat oxygen sensor will have a gap of time between the pre-cat sensor switching voltage and itself. This is often normal during a sudden fuel event that the catalytic converter, even when good, cannot instantly clean up.
When is the P0420 code Detected?
Three way catalytic converter Bank 1 does not operate properly. –
Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.
P0420 TOYOTA Possible Symptoms
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 TOYOTA Possible CAUSES
P0420 may mean that one or more of the following has happened
- 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
Diagnose Tools, what do I do next?
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.
Also, Read P0340 NISSAN Fault Code Problem Solution in Our 2nd Website
Diagnose Tools & 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.
On some vehicles such as some Subaru models, an ECM reflash will fix the problem. As you can see a P0420 can be caused by many things, so if you have any doubts as to whether you can fix the problem yourself, please seek the advice of a professional technician.
Diagnose Tools & DIY friendly tips include:
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P0420 TOYOTA – Catalyst System Efficiency Below Threshold Bank 1 Diagnosis Video
