How to Fix OBD2 Code P0442: Easy Procedure for Your Car

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OBD2 scanner showing P0442 code

One of the most common OBD2 codes is P0442 (Main Catalyst Efficiency Below Threshold Bank 1). The possible causes are converter deterioration or malfunctioning, leaks on the exhaust system, or faulty O2 sensors. Before you have your car serviced, learn how to fix OBD Code P0442 first with this tutorial.

To fix the OBD2 code P0442 reading on your OBD2 scanner, check the root cause of the check engine light illumination. Replace the parts that need replacement. If the catalytic converter is too damaged, replace it after checking on the 100,000-mile manufacturer warranty.

What does the P0442 code mean?

The P0442 trouble code means the first catalytic converter on your car is working below standard levels. Consult your car manufacturer's manual for specific instructions on what to do next.

The catalytic converter is a device that directly contributes to air quality and is the common cause of OBD2 P0442 codes. You can find it on the exhaust system of cars and other internal combustion engines, designed to reduce the emissions from their tailpipe by chemical reactions primarily converting toxic gases into less harmful compounds.


  • Check engine warning light
  • Engine stalling or misfiring
  • Increasing tailspin emissions


  • Defective catalytic converter
  • Non-functioning catalyst
  • Coolant temperature sensor malfunctions
  • Malfunctioning of air pressure sensors
  • Poor air to fuel ration
  • Engine misfires
  • Leaky head gasket
  • Malfunctioning for the 3-way catalytic converter
  • Leaking exhaust system
  • Faulty O2 sensors
  • Poor electrical connection of the O2 sensors
  • Damaged wiring to the O2 sensors

Is the P0442 code serious?

The severity of this code can vary greatly. If the faulty catalytic converter is the problem, cars may not start, have trouble starting, or frequently stall. In such cases, vehicles will be significantly underpowered and unsafe to drive until repaired. 

But if there is no issue with a catalytic converter, then it should never cause major problems. Don't be lenient, thou; always check for other possible causes before driving your car again. 

The car won’t run well, the engine will lose power and perform poorly, or it can cause significant engine damage. Driving with a bad catalytic converter is no good.

How can you fix the P0442 code?

1. Determine the root of the P0442 trouble code

If you have a defective catalytic converter, replace your catalytic converter. However, since it is not the root cause of the trouble code, dig deeper. Several factors contribute to a defective catalytic converter:

  • Engine misfires
  • Leaking head gasket or high oil consumption
  • Non-functional catalyst

If you have a defective OBD-II system or wiring harness, make sure to inspect and fix that first before replacing your catalytic converter. Closely assess other sources for the P0442 trouble code, such as airflow sensors, oxygen sensors, poor air to fuel ratio, or bad connections to the O2 sensors.

2. Replace the faulty parts

If the issue roots from the sensors (oxygen, mass airflow, manifold air pressure, coolant temperature), replace them.

Sometimes, faulty wiring or poor electrical connection may cause the problem. Take care of these, too. Check why your car misfires, such as the spark plugs, plug wires, coils, or fuel-delivery system. 

3. Check your mileage warranty

Check your 100,000-mile warranty on catalytic converters first before you replace them. If still covered with the warranty, check with your auto dealership on what they can do about it.

To check the mileage warranty, inspect the vehicle identification number (VIN), then call or visit the auto dealership's service department. 

4. Replace the catalytic converter

Catalytic converter

If there are no other sources for the trouble code P0442, it is time to replace your catalytic converter.

Unfortunately, though, replacing your catalytic converter is not cheap. It can range from $900-2500, including the labor costs, with the replacement converter taking up the bulk of the cost.

Hacks for Cleaning Your Catalytic Converter

However, you can try these hacks if you're not ready to replace the catalytic converter.

Do an Italian Tune-up

Drive your car at the top speeds on a stretch of an open road, ease on the accelerator, and repeat the process to open up the clogged converter. However, you should do this only at your risk since any further damage to your car may cause you trouble with your insurance.

Do this only if you think your car's converter is not clogged up.

Add fuel additives

This step is a precautionary measure rather than a solution. Most fuel manufacturers add fuel additives to make your car perform better with less carbon buildup.

You can also try draining your car and pour a gallon of clean gasoline with additives into your tank to help flush out the fuel lines and the catalytic converter. Take it to a test drive to see if it solved the problem.

Wash your converter

Soak your converter overnight in hot water and degreaser, then rinse using a pressure washer to remove contaminant buildup. Dry it thoroughly before putting it back. However, the downside to this is you can't use your car for at least 3 days.

How to Check If Your Catalytic Converter is Beyond Repair

You can observe these indicators if your converter is beyond repair:

  • Rotten egg smell from the tailpipe
  • Rattling sound on the converter when your car is in idle
  • Location of the converter feels hot

OBD2 Code P0442 FAQ

What happens if you don't fix the catalytic converter?

Catalytic converters function to filter contaminants from your car's exhaust stream, preventing the buildup that leads to difficult starts and poor performance. There are some critical points for maintaining these essential components so they don't become a thorn in your side.

What would you do if your catalytic converter went bad and you can't afford to replace it? Unfortunately, driving without the component will lead to steep fines. Most states require passing the emissions testing before you can drive your car.

For the most part, though, replacing the defective catalytic converter falls under your moral obligation to prevent environmental pollution, poor air quality, and health hazards to the respiratory system.

What does the main catalyst below the threshold mean?

This code indicates that the efficiency of the emission of the main catalytic converter has fallen below its minimum allowable limit. The catalytic converter controls exhaust-mounted emissions of oxides of nitrogen, hydrocarbons, and carbon monoxide. This catalyst is also often called a 3-way catalyst because of the 3 gases it converts.

What does P0420 Catalyst System Efficiency Below Threshold Bank 1 mean?

A P0420 code reading on your OBD2 scanner simply indicates that your car's bank 1 catalytic converter is underperforming, usually caused by a malfunctioning O2 upstream sensor.


If you have a P0442 code, don't panic. You may need to replace your converter or O2 sensor. The best thing to do is learn how to fix the main cause of the problem first. 

If you’re new to using an OBD2 scanner, check this how-to guide. We hope you find this tutorial beneficial, especially if you're driving your first car and experienced your first trouble code. Feel free to share this article if you think it can help your friends.