How to Troubleshoot & Fix P0420 Jeep DTC Code? (Ultimate Guide)

Being a Grand Cherokee owner, it is quite common to experience sudden DTCs such as P0420. Other Jeep variants, like Patriot and Wrangler too, are not safe from this code.

Fortunately, this problem has some straightforward causes and remedies, allowing you to fix it pretty simply at home without spending tons at a garage. 

So buckle up, and let’s learn more about the P0420 Jeep Grand Cherokee code, Wrangler, and Patriot and how to get rid of it easily.

What Does P0420 Jeep DTC Code Mean?

The P420 is a diagnostic trouble code for OBD-II-enabled vehicles. For Jeep vehicles with V6 or V8 diesel engines, such as Wrangler, Patriot, or Grand Cherokee, the P0420 code specifies that catalytic converter efficiency is below the threshold. 

However, there would be two catalytic converters for some variants of Jeep with dual exhaust systems. 

In such cases, the code would specify which catalytic converter fails to do its job, denoting the system as Bank 1 or Bank 2.

If we break down the DTC P0420, we get the following estimations:

  • P = OBD-II powertrain (engine and transmission) trouble code.
  • 0 = Generic trouble code following SAE standards.
  • 4 = The catalytic converter efficiency.
  • 20 = Specific fault index. (In this case, it’s a catalyst efficiency below the threshold.)

In Jeeps, there are two oxygen sensors with each catalytic converter. The first one detects the composition of gases from the raw exhaust coming from the engine cylinder.

The second oxygen sensor is attached at the end of the catalytic converter and detects how much the exhaust gas has been refined. 

Hence, the ECM analyzes the difference in the data from each sensor to know the efficiency of the catalytic converter.

Therefore, if we sum up the code, P0420 means the downstream oxygen sensor attached to the catalytic converter fails to detect pollutant-free incoming exhaust.

What Causes the Catalytic Converter Issue and P0420 On the Jeep?

Now that you know what the P0420 code means on Jeep vehicles like Grand Cherokee or Wrangler, let’s look for the causes of this issue. The most common causes for which the code is stored include the following:

  • Worn or Damaged Catalytic Converter.
  • Clogged Catalytic Converter
  • Faulty Downstream Oxygen Sensor
  • Leakage in the Exhaust System
  • Wiring Issues in the Oxygen Sensor Connector
  • Voltage Fluctuation Due to Temperature

Read Also: How to Troubleshoot and Fix P0513 Jeep DTC Code? (Ultimate Guide)

How to Troubleshoot & Fix P0420 Jeep DTC Code?

You have come to your desired destination, where you’ll learn all possible methods to get rid of the P0420 code in your Jeep Grand Cherokee, Wrangler, or Patriot. These fixes work the same for all variants of Jeep with V6 or V8 diesel engines.

1. Inspect and Fix Wiring Issues

Let’s get started with the easiest and cheapest way to fix the issue. Sometimes the wiring harness that connects the oxygen sensor with ECM becomes faulty due to corrosion or messed up connectors.

The oxygen sensor may malfunction or transmit inaccurate data via spiked voltages if the electrical connection between it and the Jeep’s computer is flawed. 

As a result, the P0420 error code could result from the vehicle’s computer mistakenly detecting a catalytic converter issue.

Although this is the least common cause for the P0420, giving it a shot is no big deal. 

You may check the voltage and continuity of the wiring connections with a multimeter to identify any potential wiring problems. It might be necessary to fix or replace the wiring if a bad connection is found.

2. Check and Replace Oxygen Sensor

Considering all the wiring and connection from the oxygen sensor harness is up to the market, let us skip to the second easy way to avoid P0420. 

The oxygen sensor is responsible for figuring out how much oxygen is in the exhaust gases and relaying this data to the Jeep’s computer.

To maximize engine performance and reduce pollution, the computer utilizes this information to decide how much fuel to inject into the engine. Sometimes it also leads to altering the air/fuel ratio.

Hence, the oxygen sensor’s failure could lead to incorrect data being transmitted to the Jeep’s computer. 

This may result in the P0420 code because the computer may wrongly assume a catalytic converter issue.

You can use a multimeter to check for the functionality of the downstream oxygen sensor. If you get an erratic reading, the oxygen sensor might be faulty and require replacement. 

For this procedure, you might need to pay around $270 or more, including the cost of the new oxygen sensor and labor charge.

Read Also: How to Troubleshoot and Fix P0562 Jeep DTC Code? (Ultimate Guide)

3. Eradicate Interference of High Temperature

If your oxygen sensor is in good shape, it is time to inspect if the high temperature of the exhaust is messing up with the reading. Exhaust gas coming out from the engine cylinder possesses an extremely high temperature.

Sometimes the downstream oxygen sensor being too close to the exhaust becomes interfered with by the temperature and results in variable voltage readings and spikes. 

This variable data originating from the oxygen sensor triggers the ECM to show P0420 DTC.

Although it is a very unusual and less common cause, spending only $6-$8 is worth more than spending hundreds of dollars. All you need is a catalytic converter extender or spark plug fouler.

Install this device between the oxygen sensor and catalytic converter to allow the exhaust gas to dissipate the heat and send the correct reading.

Source: https://www.youtube.com/watch?v=hkoWhTjC_aQ 

4. Remove Leakage in the Exhaust System

A P0420 code may show up if there is a leak in a Jeep’s exhaust system. Leaks can let too much air into the system, resulting in incorrect data being sent by the oxygen sensor to the Jeep’s computer. 

This may result in the computer accidentally identifying a catalytic converter issue and setting off the P0420 code. 

The amount of toxic pollutants released from the engine is decreased thanks to the catalytic converter.

The catalytic converter might not function effectively and lower the emissions to the right level if excess air enters the exhaust system due to a leak. 

Depending upon the location and size of the leakage, you might spend around $100-$200 for patching up via welding.

Read Also: How to Troubleshoot & Fix P06DE Jeep Wrangler DTC Code?

5. Clean Clogged or Dirty Catalytic Converter

The main function of the catalytic converter is to reduce the presence of toxic gasses emitted from the engine. 

There is a honeycomb-shaped structure that filters out the pollutants. Over time, it becomes clogged because of debris and specks of dirt.

Therefore, the efficiency of the catalytic converter reduces with time due to over-clogging, resulting in showing the P0420 code. You can clean the catalytic converter in two different ways.

Firstly, use a catalytic converter cleaner in the fuel tank and rev up the engine to automatically clean the clogged filter. 

If that does not work, you must manually clean the catalytic converter by soaking it in the detergent solution.

Ensure clearing the code from the system after reinstalling the catalytic converter and if the code P0420 reappears. 

You may need assistance from the mechanic to remove the catalytic converter, which can charge you around $75-$100 for an hour of service.

6. Replace Catalytic Converter

Finally; the faulty catalytic converter is the worst-case scenario and most common cause for the P0420 code on a Jeep. 

According to car complaints, 30 complaints for Jeep Patriot and around 132 technical service bulletins have been reported against Jeep Grand Cherokee.

If your catalytic converter is damaged or worn out, the only solution is to replace it with a new and compatible one. 

Swapping the catalytic converter is a very tedious job. In some model years of Jeep, the position of it is shifted under the engine, making it more difficult to get access.

Therefore it is recommended to seek professional help to replace the catalytic converter in your jeep and reset the code. 

This procedure can cost you $1500-$2500 or more, including the service and labor charge.

Read Also: How to Troubleshoot & Fix P2181 Jeep DTC Code? (Ultimate Guide)


The following FAQs from the users about the P0420 Jeep code can enlighten you more about fixing and handling the issue.

Can you drive a Jeep Grand Cherokee with the P0420 code?

You can drive a Jeep Grand Cherokee with a P0420 code, as it won’t hamper the vehicle’s performance. But it’s recommended to be diagnosed and repaired as soon as possible to prevent potential long-term damage.

How much does it cost to fix Jeep Grand Cherokee P0420 code?

Fixing the P0420 code on Grand Cherokee depends upon the service it requires. Replacing the oxygen sensor costs $150-$250. But swapping the entire catalytic converter can be up to $2500 or more, including labor charge.

Does P0420 mean I need a new catalytic converter?

You don’t always need a new catalytic converter to fix the P0420 code. Sometimes a bad oxygen sensor or clogged catalytic converter also sets the P0420 code, which you can easily fix.


If P0420 hits your Jeep Grand Cherokee, Wrangler, or Patriot, it is advised to get it treated early. 

Because this issue has the potential to damage your engine in the long run, which can be very expensive to fix.

You can diagnose and fix it if you have the tools and previous experience. On the other hand, let the job be handled by a professional mechanic.

Read Also: How to Troubleshoot & Fix P0522 Jeep DTC Code? (Detailed Guide)

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