P0420 Ford: Causes, Symptoms & Fixes

When talking about diagnostic codes for your Ford, we must mention the P0420 error code that may appear on your vehicle’s control module. This code refers to a malfunction with the three-way catalytic convertor or to its inefficiency in functioning as expected.  

Fortunately, even though the code sounds pretty dangerous, it is not as serious and won’t cause many problems if fixed early. 

So, in this article, we will discuss all things you need to know about P0420 Ford. We will talk about its common symptoms, causes, and how to fix it. 

What does P0420 Ford mean?

What does P0420 Ford mean?

P0420 for Ford codes for “Catalyst System Efficiency Below Threshold (Bank 1). It essentially means that catalyst efficiency on Bank 1 has been detected to be underperforming by the Engine Control Module or ECM.

The front oxygen sensor is the heated oxygen sensor 1, and the rear oxygen is the heated oxygen sensor 2. They are at the front and back of the catalytic converter, respectively. The ECM constantly observes the switching frequency ratio of these two sensors 

When ECM detects a matching switching frequency ratio from the oxygen sensor 1 and 2, your Ford will show the P0420. It means the three ways catalyst converter of your vehicle is not working accurately, and it has insufficient capacity to store oxygen.

What are the symptoms of P0420 Ford?

Your Ford shows many obvious and obscure symptoms when the P0420 code is triggered. If you are aware of the symptoms caused by the P0420 code beforehand, then you can solve those issues as soon as possible and lessen the amount of damage.

So, we are going to describe the symptoms that are caused by the P0420 code.

Engine Light

If you see that the engine light is always ON, you should know that there must be a problem with your Ford. Engine light being continuously ON is one of the most common symptoms of P0420.

Engine Power

If you face any insufficiency or shortage of engine power of your Ford, it could indicate the malfunction of the catalyst converter or the P0420.

Fuel Economy

Your car cannot utilize its fuel to the fullest due to P0420, which results in poor fuel economy. It will use a lot of fuel to go only a short distance.

Fuel Smell

Your Ford will have a powerful odor if too rich fuel or too poor air enters the chambers of combustion due to the P0420 code. This smell can sometimes be similar to rotten eggs or sulfur.

Engine Misfire

Catalyst converter malfunction of your Ford can cause the engine to misfire, meaning the car cylinders do not produce any or enough power. So, your car will not speed up. When you press on the throttle, the engine misfire will cause your car to stumble.

What are the Causes of P0420 Ford?

There are many reasons that can cause your Ford’s P0420 code to be displayed. If you are aware of them, it will be possible for you to find a solution to those problems.

So, the causes that trigger the P0420 code by your vehicle are mentioned below.

Catalytic Converter 

A busted catalytic converter is one of the most common reasons for the P0420 code to be triggered.

The catalytic converter can get damaged due to clogging as a result of overuse, engine misfire, and an imbalanced air to fuel ratio.

Tainted oil and the wrong placement of the catalytic converter also cause your Ford’s P0420 to be displayed.

Fuel Injector

If there are any leaks in the fuel injector of your Ford, a massive amount of fuel will enter the combustion chamber. Too much fuel in the combustion chamber will cause the P0420 code to show up.

Oxygen Sensors

When both oxygen sensors show very close readings, the P0420 code is displayed by your Ford.

If the sensors are damaged, they might cause incorrect reading and activate the P0420 code.

Sensor Wiring

The oxygen sensors get worn out over time since they are always next to the exhaust, and the downstream oxygen sensor gets damaged more frequently as they are very far from the ECM. Both of these activate the P0420 code.

Air Filter

A clogged air filter caused by a damaged muffler, exhaust pipe, or catalytic converter will trigger the P0420 code.

Engine Oil

Your engine oil becomes contaminated mainly due to a long gap between oil changes. Bad engine oil causes the P0420 code to go off.

Also, if you use the wrong fuel, such as the leaded fuel rather than the unleaded, then the P0420 code will go off.

Exhaust Leak

If there is any leak in your exhaust system, toxic fumes will enter your car’s cabin rather than leave through the tailpipe. This will cause your vehicle to show the P0420 code.

Coolant Temperature Sensor

A faulty temperature sensor cannot detect the engine temperature, which makes the fuel-rich with gasoline. 

Rich fuel mixture will interrupt the interaction between the exhaust and the oxygen sensors. This will trigger the P0420 code.

Ignition Timing

Defected ignition timing can slow down the firing time of the spark plug and cause the P0420 code to be displayed.

How to fix P0420 Ford?

How to fix P0420 Ford

The fixing of the P0420 code of your Ford depends on its cause. First, check the reason behind the code and then fix it accordingly.

Following these can almost always fix the P0420 code.

  • Repair the catalytic converter.
  • Clean out the mass airflow sensor and oxygen sensors.
  • Replace the fuel regulator, fuel pump, and fuel injector.
  • Remove the damaged air filter and get a new one.
  • Replace the engine coolant system and the thermostat.
  • Repair the exhaust leak.

How to diagnose P0420 Ford?

The fixing of the P0420 code of your Ford depends on its cause. First, check the reason behind the code and then fix it accordingly.

Following these can almost always fix the P0420 code.

  • Make sure there are no other codes for the engine present.
  • Look for leaks in the exhaust system.
  • Check the oxygen sensors.

Is P0420 Ford Serious?

The severity of the P0420 code for your Ford is moderate. However, if left for a long time, it can cause extreme damage to your car. So, you should get the P0420 code fixed as soon as possible.

What’s The Cost to Fix P0420 Ford?

If you take your Ford to a car repair shop, then the diagnosis of P0420 will cost you the wage of one hour. This could be somewhere between $80 to $160.

The cost to fix the P0420 code of your Ford depends on the repairing part of your car. Along with the price of the part, they will add the diagnosis price.

Final Words

Now you know everything about code P0420 Ford. Now that you know the symptoms of this code, you can easily diagnose it before having to consult your mechanic. And hopefully, even fix it yourself!