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P0420 Toyota Previa – Symptoms


P0420 Toyota Previa

This page is intended to help you solve the problem of Toyota Previa Fault Code P0420. Covers the meaning of Toyota Previa P0420, symptoms, causes, and possible solutions. On the Previa, OBDII P0420 is usually caused by a faulty oxygen sensor, but there can be other causes as well.

One of the most common fault codes on all Toyota vehicles is P0420. This code refers to a number that is given to you when you connect your Toyota Previa to an OBDII scanner. No matter what model you have, this OBDII code has the same meaning for all of them.

P0420: Catalyst System Efficiency – Below Threshold

Toyota Previa P0420 OBDII Code Defined

Toyota Previa Code P0420 Symptoms

P0420 It is an OBDII fault code. The code technically means:

Catalyst system efficiency below threshold

Your Previa has at least two oxygen sensors, one before and one after the catalyst. Among the many tasks that oxygen sensors have is to measure the levels of emissions entering and leaving the converter.

When the readings of the upstream and downstream oxygen sensors show similar readings, the vehicle will trigger the service engine soon light (P0420).

Your vehicle’s software believes that the catalyst is no longer doing its job.

If your vehicle has the P0420 code, it will not pass emissions, so keep that in mind.

Toyota Previa P0420 Code Symptoms

Toyota Previa P0420 OBDII Trouble Code

The P0420 code on a Toyota Previa will often be thrown if one of your oxygen sensors are not working properly. Normally the code will be thrown by the upstream oxygen sensor (before the converter).

There are usually no driving problems associated with P0420. For most people, the first sign that something is wrong is when the engine maintenance light comes on.

These are typical symptoms that something is wrong when you have the P0420 code.

  • Mileage- It may or may not suffer depending on the degree of catalyst clogging.
  • Power loss– It is a really strange feeling to drive a vehicle with a catalytic converter that is going out. Normally, the engine runs well at idle and with a light load. When the engine is put under heavy load, it feels like it is running out of gas. It is very similar to the symptoms of a bad fuel filter.
  • service engine light– This is often the only symptom of Toyota Previa code P0420.

Related: P0442 Toyota Previa

Main Causes of P0420 on the Toyota Previa

OBD2 Code P0420 Toyota Previa

There are many things that can cause the P0420 fault code on your Previa. Here are the most common ones.

  • Oxygen sensor– The P0420 code is thrown when the oxygen sensors on both sides of the exhaust have very similar readings. When the oxygen sensor is bad, it can cause a false reading and trigger the code. If the engine does not show any of the performance decreases associated with a bad catalyst, it is very likely the oxygen sensor (if you haven’t already noticed the loss of performance).
  • Catalyst– The catalyst is responsible for eliminating all possible contamination from the Previa’s exhaust pipe. Over time, they can become clogged. Although modern catalytic converters are supposed to last the life of most vehicles, there may be some underlying problem if it has become clogged.
  • O2 sensor Cabling– Over time, the oxygen sensor wiring can become damaged. It is especially volatile since it is right next to the hot exhaust at all times. The downstream oxygen sensor wiring is especially volatile since it is so far from the ECM (more distance to travel.
  • Preview Timing– If your Previa has a misfire or the exhaust gas timing is incorrect, this may affect the gases going to the O2 sensors enough for the P0420 code to be recorded.
  • Exhaust Drain– If there is a noticeable exhaust leak coming from the vehicle, it may change what the O2 sensors register enough to throw the P0420 code.
  • Engine temperature sensor– If the computer does not know what the engine temperature is, it will keep the fuel mixture rich. When the fuel mixture is rich, the exhaust seen by the O2 sensors will be out of range and could trip the sensor.

Toyota Previa Code P0420 Possible solutions

Often the oxygen sensor is the cause of P0420. Specifically, it is usually the O2 sensor or sensors located on the front side of the catalyst.

But don’t be surprised if it doesn’t. It would be a good idea to check the exhaust for leaks first. You should be able to easily hear an exhaust leak under the vehicle.

Unless you have an exhaust leak, you’ll probably need to check the O2 sensors and/or catalysts. Here are a couple of good guides to help you do it.

Good luck figuring out the cause of P0420 on your Toyota Previa. If there is any inaccuracy, or something that you think could improve the article, do not hesitate to comment or send it by message. Thank you.


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