OBD2 Codes

Dodge P0420 – Meaning, Causes, Symptoms, & Fixes

What Does Dodge Code P0420 Mean?

  • Dodge P0420 definition: Catalyst system efficiency below threshold (Bank 1)
  • Issue Severity: MODERATE – Extended driving with this code can cause internal engine damage.
  • Repair Urgency: Get this code fixed as soon as possible to avoid further damage to your emission system and possible engine damage.
  • Diagnosis: The most common cause of Dodge P0420 is a bad catalytic converter, but it can be caused by anything from a faulty oxygen sensor to a rich or lean running condition, or misfires. Because there are so many variables that could cause this code, the best cost savings is to take your car into a shop to have it diagnosed as quickly and accurately as possible.

Find a Certified Shop

We've partnered with RepairPal to recommend trustworthy shops in your area. Enter your details to see certified shops near you that offer upfront estimates, guaranteed fair pricing, and a minimum 12-month, 12,000-mile warranty.














The function of the catalytic converter is to break down harmful pollutants that are created by your Dodge during the combustion cycle and convert them into less harmful gases. Code P0420 indicates that the catalytic converter is not functioning efficiently, therefore increasing the output of harmful pollutants by the vehicle.

Dodge P0420 Causes

The most common reason for check engine code P0420 is catalytic converter failure, but there are other potential causes for this code. It’s important to look for other codes that could indicate the root cause of converter failure, such as misfires or an incorrect air-fuel ratio.

  • Worn or internally failing catalytic converter (Most Common)
  • Faulty oxygen sensor
  • Faulty air-fuel sensor
  • A leak in the exhaust system
  • Misfire (the root cause of converter failure)
  • Rich or Lean air-fuel ratio (the root cause of converter failure)
  • Leaded Gasoline (the root cause of converter failure)

Dodge P0420 Symptoms

  • Check Engine Light is on
  • Lack of power from the engine
  • Decreased fuel economy
  • Rotten egg or a sulfur smell

How Do I Fix Dodge Code P0420?

The first step is to get it diagnosed to figure out what is causing the catalytic converter fault. 

If you’re having catalytic converter issues and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

> Find a RepairPal Certified Shop Near You

How Much Does It Cost to Fix Dodge Code P0420?

P0420 can be caused by anything from a bad sensor to a failed catalytic converter. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0420 code.

Right shop, right price

We've partnered with RepairPal to recommend certified and trustworthy shops in your local area. 

  • Upfront cost estimates
  • Minimum 12-month, 12,000-mile warranty
  • Fair price guarantee

Possible Repair Costs for Dodge P0420

Once properly diagnosed, P0420 may require one or more of the following repairs to resolve the underlying issue. These prices are based on national averages and include parts and labor. Your cost may differ depending on your location and type of vehicle.

DIY Steps to Diagnose Dodge Code P0420

If you’d like to try to fix code P0420 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an advanced-level diagnosis and repair and not recommended for beginners. Diagnosis can be a time and labor-intensive process for inexperienced DIYers.

 

DIY difficulty level: Advanced

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):

STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.

Use FIXD to scan your Dodge to verify P0420 is the only code present. If other codes are present, they must be addressed first.

STEP 2: EXAMINE THE EXHAUST SYSTEM FOR DAMAGE AND LEAKS.

Pay close attention to the exhaust manifold, gaskets, and exhaust pipes pre-catalytic converter. If any leaks are found, repair the leak, clear the code, and complete several drive cycles to verify that was the fix.

STEP 3: CHECK THE DOWNSTREAM O2 SENSOR.

With the vehicle running and at normal operating temperature, use the FIXD live data feature or a digital multimeter to check the voltage reading of the downstream O2 sensor. The downstream O2 sensor produces a relatively steady voltage reading of approximately 0.45V if the catalytic converter is functioning properly. If the voltage of the downstream O2 sensor is constantly jumping between 0.1V and 0.9V, the catalyst is worn and the catalytic converter needs to be replaced.

 Common P0420 diagnosis mistakes

Oftentimes, this code is thought to be a faulty O2 sensor or A/F Sensor. While this is a possibility, the most common problem is a faulty catalytic converter. Do not overlook other codes that are paired along with P0420. Codes like P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308 are misfire codes, and these codes require misfire diagnosis. If the catalytic converter is replaced without repairing the misfire, the new catalytic converter will go bad again. Also, make sure you don’t have codes P0174, P0171, P0172, or P0175 which can mean the engine is running rich or lean, which can burn out your catalytic converter. If these codes or any other codes are present, they should be addressed first.

Still Need Help Fixing Dodge Code P0420?

If you’ve followed the steps above and are still experiencing Dodge check engine code P0420, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you for proper diagnosis and fair pricing.

Justin-Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

Justin Hughes
Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

    You may also like

    4 Comments

    1. just replaced both 02 sensors and bank 1exhaust manifold code p0420 code came back up ? engine runs good still, is the convertor shot ?

      1. Replace temp sensor

    2. my 2008 Avenger is having the same issue but also has a code for the transmission. Took it to the shop and they said its clogged convertor and needs replaced and that’s also why the transmission code is in. Now she seems to be running hot also. I had both O2 censors replaced because it was the cheapest way to go and first step. Exhaust will run me 1300$ for convertor replacement. Any thoughts, im thinking about getting another opinion

    3. run it until warm, and beat up the cat converter with a rubber mallet. if you’re lucky, you’ll knock some of it loose.

    Leave a reply

    Your email address will not be published.

    More in OBD2 Codes