P0420 Toyota – Causes and How To Fix The Error Code

Clyde Goering Image
Written by Clyde Goering

May 6, 2020

p0420 toyota

Toyota P0420 OBDII Code Defined

exhaust system schematic

P0420 Toyota Code is triggered when your car’s engine control unit detects a fault in the catalytic converter. Two O2 sensors are often used to identify the problem: one at the catalytic converters, and the other in the front section of the exhaust. The job of these sensors is to determine the efficiency of your car’s catalytic converter.

So, the P0420 error signifies that there is an urgent problem with the catalytic converter’s efficiency standings. P0420 Toyota Code is one of the hardest errors to diagnose correctly. Even when you thought you found and corrected it, you would drive for about 100 kilometers and experience the same old symptoms. This is compounded by the fact that there is a ton of false information on it out there.

Signs and symptoms of the P0420 Toyota Code

You may not see any other sign other than the P0420 Toyota Code itself and “check engine” light on your dashboard. These are ambiguous signs as there may be other problems with your car’s engine, which could be affecting the smooth operation of your catalytic converter.

In the most extreme of all cases, you may experience rough acceleration, hard shifting, and rough acceleration. To be always on the safe side, consider fixing these problems immediately after detecting them:

  • Misfires
  • Considerably slow acceleration
  • Blue smoke emanating from the tailpipe
  • Motor oil burn
  • Lean mixture and rich mixture

Possible causes of P0420 Toyota Code

  1. These are the common causes of the P0420 Toyota Code: The most often reported cause of the P0420 Toyota Code is the issues of the catalytic converter. Sometimes it has something to do with the age of the device – when the catalytic converter is too old to keep working smoothly. The P0420 Toyota Code can still occur even after replacing an old catalytic converter with a new one. Nine out of ten times, such cases occur because the catalytic converter is not genuine. Cheap catalytic chambers don’t work as correctly as genuine devices.
  2. Putting leaded fuel in a system that’s supposed to be unleaded: Putting leaded fuel in a system that’s supposed to be unleaded is a gross mistake, but you will be surprised by how often it occurs. This misplacement is one of the chief causes of the P0420 Toyota code. But why would it cause problems, yet it is the same type of fuel with a minor difference in lead content? It is partly because these two fuels combust differently, and the exhaust is different as well. It is important to note that leaded fuel is still being used in some parts of the world amidst the ever-increasing opposition to its use.
  3. The poorly installed catalytic chamber: Sometimes your catalytic converter may be functioning correctly except that it is installed wrongly. Installing your device too far back on the exhaust pipes deprives it of the threshold heat it needs, eventually causing the P0420 Toyota code.
  4. Failed O2 sensors: There is a strong chance one or both two O2 are troubled. If there is a connection problem between them or if one or both fail to work, you are almost sure of receiving the P0420 Toyota code.

Besides the issues of the catalytic converter, the following minor problems may be responsible for the P0420 Toyota code.

p4020 toyota
  • Damaged or malfunctioning upstream O2 sensor
  • Damaged or malfunctioning downstream O2 sensor
  • Oil burn (which ends up running the catalytic converter)
  • Lean/rich (which ends up ruining the catalytic converter)
  • Misfires (which ends up ruining the catalytic converter)
  • Spark timing issues
  • Contamination of the fuel oil
  • Leakage in the exhaust manifold
  • Problems with coolant temperature sensor
  • Leaking fuel injectors

Those are the causes of the P0420 Toyota code, but how do you correct the situation?

Possible solutions to the P0420 Toyota Code

Below are possible solutions to the P0420 Toyota Code – “possible” because the cause could be none of the above reasons. Also, you should not replace parts of the exhaust system without proper diagnostics lest you waste your money and time on a remedy that won’t bring any effect. It is always a great idea to seek the assistance of a competent mechanic who won’t misdiagnose your car or offer a bogus solution. Here are some of the solutions to the P0420 Toyota code.

  • Replace to an original or genuine catalytic converter
  • Replace your front O2 sensor
  • Replace your catalytic converter
  • Replace your rear O
  • Fix rich /lean mixture
  • Repair the faulty wirings
  • Fix the misfires
  • Fix oil burn problems

Important note on P0420 Toyota Code:

There are several reasons why the catalytic converter may fail. Sometimes these problems have their origin elsewhere on the exhaust system. So, you don’t want to replace your old catalytic converter with a new genuine one only to experience the same issues again (this is one of the causes of the recurrence of the P0420 Toyota code.

Before replacing any part of the catalytic chamber or any other part of the exhaust system that you may think is the source of the issue, consider correcting any other problem that may be contributing to the P0420 Toyota Code and wait for the results. You should only take drastic measures when you don’t see an improvement.

Also, why not prevent the P0420 Toyota code before it’s too late? Yes, take your car for check-ups at least twice every year. Keep an eye on the exhaust smoke – if it’s blue, your car is burning the oil; white smoke means your vehicle is going hard on the water; grey/black smoke means your car is burning a rich mixture.

Bottom line:

The P0420 Toyota Code is one of the hardest codes to diagnose correctly. If you do, there is a strong chance it has something to do with a problem in the catalytic converter. Besides the problems of the catalytic converter, the culprit could be: spark timing issues, contamination of the fuel oil, leakage in the exhaust manifold, problems with the coolant temperature sensor, leaking fuel injectors, among others.

It is essential only to respond to correct precise diagnosis lest you incur huge costs fixing a problem that doesn’t even exits. You can as well prevent the P0420 Toyota Code by being proactive and taking your car for check-ups regularly.

Clyde Goering Image
Written by Clyde Goering


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