Toyota fault code p0420

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Toyota fault code P0420 – causes of catalyst failures and ways to solve the problem

Toyota fault code p0420

Toyota fault code p0420

We live in a world that is in step with the times. Computer technology as early as the end of the last century did not pass by automobile production. The first car with on-board diagnostics was introduced by Volkswagen in 1968.

On-board diagnostics

Every driver who has a modern car knows about the on-board diagnostic system in the car, with which you can find the car’s malfunctions. In a literal sense, the car itself determines where and what is its malfunction, and issues a certain diagnostic code to the device, by means of which the driver or the master determines the malfunction and seeks repair methods.

Fault code p0420

A fairly common diagnostic fault code. In the information space, and simply in everyday life from the owners of cars you can hear a lot of information, rumors and advice about this code. Let’s consider what does it mean, what kind of malfunction can it talk about, what methods of solving this problem exist.

What does the fault code p0420 mean?

You see, as you have a control indicator on the dashboard turned on. You go to the car service or, possibly, scan the car yourself and find out that the problem is represented by the fault code p0420. After displaying the codes, first make sure that p0420 is the only single code. If not, it is necessary to diagnose other codes, since they can call the code p0420. The reason for this is that the converter is the end result of the diagnosis. In principle, if there is a problem with one of the sensors in the engine or exhaust, this can lead to a decrease or increase in the amount of fuel entering the engine.

So, we see the code, and if there are no other than p0420, it often means that the efficiency of your catalytic system is lower than it needs to be measured by your oxygen sensors. This means there was a problem with either a catalytic converter, or with oxygen sensors, or both. The purpose of the catalytic converter is the destruction of harmful pollutants created during the combustion cycle. Using fine platinum and gold mesh for exhaust gas filtration, the catalytic converter is able to reduce emissions from the exhaust pipe. The catalytic converter has two oxygen sensors. One oxygen sensor is located in front (upstream) of the catalytic converter, and the other oxygen sensor is located behind (downstream). If the front oxygen sensor is operating correctly, its readings should fluctuate when the car is at operating temperature and when working in a closed loop. If the lower oxygen sensor is operating correctly and there are no problems in the catalytic converter, its readings should remain stable. When oxygen sensors have readings that are similar to each other, this indicates that the catalytic converter does not work properly. If the voltage of the rear oxygen sensor decreases and begins to oscillate similarly to the front oxygen sensor, this means that the oxygen levels are too high, and the powertrain control module will show the fault code p0420.

Toyota fault code p0420 1

What causes p0420 fault code?

  • Damaged muffler or leaks in it.
  • Damaged exhaust manifold or leaks present.
  • Damaged exhaust pipes. A misfire in the engine.
  • Oil contamination in the catalytic converter.
  • Defective catalytic converter (most common).
  • Defective engine coolant temperature sensor.
  • Defective front oxygen sensor.
  • Defective rear oxygen sensor.
  • Damaged oxygen sensor wiring.
  • The oxygen sensor wiring is not connected correctly.
  • Damaged oxygen sensor connectors.
  • Fuel Injector Leakage.
  • High fuel pressure.
  • Use of an incorrect type of fuel (leaded).

How does the mechanic diagnose the code p0420?

  • Uses the OBD-II scanner to retrieve trouble codes stored in the PCM.
  • Considers the current data of the downstream (rear) oxygen sensor. Determines if the oxygen sensor is operating correctly.
  • Diagnose any other codes that can cause the DTC p0420.
  • If necessary, eliminates misfires, problems with ignition and problems with the fuel system.
  • Inspect the rear oxygen sensor for damage and excessive wear.
  • Checks for PCM updates if the catalytic converter is faulty. After replacing the catalytic converter, PCM updates are required.

Common mistakes when diagnosing fault code p0420

The most common mistake is the replacement of oxygen sensors before the completion of the diagnostic process. If another component causes a fault code p0420, replacing the oxygen sensors will not solve the problem.

How serious is the code p0420?

The driver does not have to experience control problems if a fault code p0420 is present. In addition to the on-board indicator, the symptoms of this DTC may go unnoticed. However, if the car is operated with an error and this problem is not solved, other components may be seriously damaged. Since there are no control problems with p0420, this is not considered serious or dangerous for the driver. However, if the code is not eliminated in a timely manner, the catalytic converter may be seriously damaged. Since the catalytic converter is expensive to repair, it is very important that the fault code p0420 be diagnosed and repaired as soon as possible.

Toyota fault code p0420 2

What repairs can fix the fault code p0420?

  1. Replace the muffler and repair leaks.
  2. Replace the exhaust manifold and repair leaks.
  3. Replace the exhaust pipe.
  4. Replace the catalytic converter (most common).
  5. Replace the engine coolant temperature sensor.
  6. Replace the front or rear oxygen sensor.
  7. Repair or replace damaged wiring with oxygen sensors.
  8. Repair or replace the oxygen sensor connectors.
  9. Replace or repair the fuel injectors that are leaking.
  10. Diagnose any repairs in case of any problems with the misfire.
  11. Diagnose and eliminate any other associated fault codes that have been stored by the Power Management Module (PCM).

Toyota fault code p0420 3


If the fault code p0420 prevents you, do not want to remove the catalytic converter, strive for the machine to comply with environmental standards, then you will have to repair and prevent it. Here are some useful tips:

  1. Special tools, such as Catalytic Converter Cleaner, purify the catalyst, thus prolonging its service life.
  2. Refuel only on proven gas stations and high-quality fuel. Otherwise, it will be necessary to replace the catalytic converter, and its cost is quite high.

Cheaper alternatives to prevent the appearance of the described error are the installation of emulators and reprogramming the system. These options will not worsen the performance of the car, and in some cases even improve it.

One thought on “Toyota fault code p0420

  1. Holly

    I have a 2006 Toyota Tundra with a code P0420. How do I know which Catalytic Converter it is?


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