Diagnose and explanation for P0420 Chevy silverado OBDII code

P0420 Code Chevy Silverado

This page will help you to troubleshoot your problem. Chevy Silverado P0420 trouble code. The Chevy Silverado's P0420 definition, symptoms, causes, as well as possible solutions is covered. OBDII P0420 can often be caused by an oxygen sensor problem in Silverado. But there may also be other reasons.

The P0420 is one of the most frequent trouble codes for all Chevy cars. This is the code that you get when your Chevy Chevy Silverado goes into an OBDII scanner. It doesn’t matter which model you have, this OBDII code has the same meaning for all of them.


P0420: Catalyst System Efficiency below Threshold


Índice de Contenido
  1. Chevy Silverado P0420 OBDII Code Defined
  2. Chevy Silverado P0420 Code Symptoms
  3. The Top Reasons for P0420 in Chevy Silverados
  4. Chevy Silverado P0420 Code Possible Solutions

Chevy Silverado P0420 OBDII Code Defined

Chevy P0420 Code Symptoms

P0420 It is an OBDII trouble code. Technically, the code stands for:

Low Catalyst System Efficiency

At least two oxygen sensors are installed in your Silverado, one just before the converter and another after it. One of their many duties is to determine the levels of emissions coming into and out the converter.

If the downstream and upstream oxygen sensors give similar readings, then the vehicle will soon turn on the service engine (P0420).

Your vehicle's software believes the catalytic convert is not doing its job.

If your vehicle has the P0420 code, it won’t pass emissions so please be aware of that.

Chevy Silverado P0420 Code Symptoms

Chevy P0420 OBDII Trouble Code

If your oxygen sensor isn't working correctly, the P0420 codes in Chevy Silverados will be displayed. In most cases, the code will trigger the oxygen sensor that is upstream of the converter.

There aren’t usually any drivability issues associated with P0420. Most people will notice the light at the top of the engine.

These are some of the symptoms you should look out for if your code is P0420.

  • Mileage- You may or not experience any problems depending on the extent of catalytic conversion blockage.
  • Perilous times for Power– It is a really strange feeling to drive a vehicle with a catalytic converter that is going out. Typically, they’ll idle ok and drive normal under a light load. Whenever the engine is put under a heavy load it’ll feel like it is running out of gas. It’s very similar to the symptoms of a bad fuel filter.
  • Service Engine Light– Often, this is the only symptom of the Chevy Silverado P0420 code.


The Top Reasons for P0420 in Chevy Silverados

OBD2 Code P0420 Chevy

You can have the Silverado P0420 trouble code for many reasons. Below are some common reasons.

  • Oxygen Sensor– The P0420 codes is thrown when the oxygen sensors on both sides of the exhaust have very similar readings. An oxygen sensor that is defective can give false readings and cause the code to be triggered. If the engine does not exhibit any of the decreased performance associated with a bad catalytic converter, it very well may be the oxygen sensor (if you haven’t noticed the performance loss yet).
  • Catalytic Converter– A catalytic converter is responsible for scrubbing out as much pollution as possible from the Silverado’s exhaust. These can become blocked over time. Even though modern catalytic convertors are designed to last the lifespan of vehicles, it is possible that there may be an underlying issue.
  • O2 Sensor Connectivity– Over time, the oxygen sensor wiring can go bad. This is because it is directly next to hot exhaust. It is more distant from the ECM which makes it even more volatile.
  • Spark Timing– If your Silverado is misfiring or the exhaust timing is off, this can affect the gasses that are actually going to the O2 sensors enough to cause the P0420 code to register.
  • Exhaust Leak– If there’s a noticeable exhaust leak coming from the vehicle it can change what the O2 sensors register enough to throw the P0420 code.
  • Sensor to measure engine temperature– If the computer doesn’t know what the engine temp is it’ll keep the fuel mixture rich. The O2 sensors will not see the mixture richly and could cause it to throw its sensor.


Chevy Silverado P0420 Code Possible Solutions

P0420 can often be caused by an oxygen sensor. Specifically it’ll usually be the O2 sensor(s) on the upstream side of the catalytic converter.

But, don’t be surprised if it’s not. Checking the exhaust first is a smart idea. It should be possible to detect an exhaust leak underneath the vehicle.

Unless you have an exhaust leak, you’ll probably need to test the O2 sensors and/or catalytic converters. These are some great guides that will help you.


It's your job to find the cause of P0420 in your Chevy Silverado. You can comment on the article or send a message if there are inaccuracies or any suggestions. Many thanks.

¡Más Contenido!

Leave a Reply

Your email address will not be published. Required fields are marked *

Go up