Ford Explorer P0420: Catalyst System Efficiency → Below Threshold → Bank 1

This page was created to assist you in troubleshooting the problem. Ford Explorer P0420 trouble code. This article covers Ford Explorer P0420 symptoms, causes and potential solutions. OBDII P0420 in the Explorer is usually caused by an oxygen sensor problem, however, there are other possible causes.

P0420 is one of the most frequent trouble codes for Ford cars. This is the code that you get when you connect your Ford Explorer to an OBDII scaner. 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

Ford Explorer P0420 OBDII Code Defined

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

Low Catalyst System Efficiency

Your Explorer contains at least 2 oxygen sensors. There are one in front and another after the catalytic convertor. 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.

Ford Explorer P0420 Code Symptoms

Your oxygen sensors may not be working correctly and the Ford Explorer's P0420 will display. Usually, 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.
• The loss of 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 Ford Explorer P0420 code.

Similar: P0442 Ford Explorer

Here are the Top 5 Reasons Why P0420 is a Problem in Ford Explorer

P0420 Trouble code can occur for many reasons. These are some of the more common causes.

• 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 Explorer’s exhaust. They can get clogged over time. Modern catalytic converters should last for the lifetime of most cars, but if they have become clogged, there could be an underlying issue.
• O2 Sensor The wiring– Over time, the oxygen sensor wiring can go bad. Because it's right beside the exhaust, this wiring is extremely volatile. It is more distant from the ECM which makes it even more volatile.
• Explorer Timing– If your Explorer 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.
• Engine Temperature Sensor– If the computer doesn’t know what the engine temp is it’ll keep the fuel mixture rich. If the fuel mixture becomes too rich it will cause the O2 sensor to see an exhaust that is out of normal range. This could result in the sensor being thrown.

Ford Explorer P0420 Code Possible Solutions

Commonly, P0420 is caused by the 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 for signs of leakage is a smart idea. An exhaust leak should sound easily beneath the car.

Unless you have an exhaust leak, you’ll probably need to test the O2 sensors and/or catalytic converters. Below are some good guidelines to assist you in this task.

You will be able to identify the cause of P0420 in your Ford Explorer. You can comment on the article or send a message if there are inaccuracies or any suggestions. We are grateful.