P0420 Code For Catalytic Converter: What It Is And How To Fix It (2024)

911 Carrera

Make

Porsche

Segment

Coupe

The P0420 code is a generic error code used by all manufacturers since 1996 when the OBD-II port for vehicle scanners became commonplace. So, whether your vehicle is a Toyota, Nissan, Chevy, Honda, Ford, or any other manufacturer, you may encounter the P0420 Catalyst System Efficiency Below Threshold (Bank 1) error code. This error code indicates there is an issue with your post-combustion emissions device, the catalytic converter. If you're wondering what the remedy is for the P0420 code, this guide will tell you all you need to know.

What Does The P0420 Error Code Mean?

The catalytic converter is used to clean post-combustion exhaust gasses that are toxic to the environment. The catalytic converter uses precious metals such as palladium, rhodium, and platinum to alter the gasses as they pass through the converter chemically.

Your vehicle's computer or Powertrain Control Module (PCM) monitors the efficiency of the catalytic converter through the use of oxygen sensors. Two sensors are mounted on the exhaust; the upstream sensor measures the oxygen content in the exhaust pre-catalytic converter and the downstream sensor measures the oxygen content of the exhaust post-catalytic converter. When the downstream sensor shows less than the desired amount of oxygen, the P0420 catalytic converter error code is set by the PCM.

What Causes The P0420 Error Code?

The most common cause of the P0420 engine code is a degraded catalyst. Catalytic converters/catalysts break down over time and can also become clogged. Cylinder misfires will significantly reduce the life of a catalytic converter if left unrepaired, as raw or unburned fuel damages them. Other possible causes of this catalytic converter code are:

• Defective coolant temp sensor
• Leaking injectors
• Cylinder misfires
• Faulty wiring
• Exhaust leaks pre-catalyst
• Defective oxygen sensors
• Faulty PCM

Symptoms Of The P0420 Error Code

The most common symptom reported for the P0420 error code is an illuminated check engine light. You may also hear a loud exhaust noise with the P0420 code present due to catalytic converters being a common target for theft. Other symptoms reported with the P0420 error code are:

• Vehicle fails emissions inspection
• Increased vehicle emissions
• Sulfur or "rotten egg" odor
• Rough idling
• Engine misfires
• Delayed acceleration

Can I Drive My Car With This Issue?

You can most likely drive your vehicle with the P0420 error code present if the catalyst hasn't melted or clogged. After a catalyst breaks down, it can cause a major restriction in the exhaust gasses. This can result in the engine no longer being able to run or severely lacking power. For this reason, we recommend getting your car assessed as soon as possible.

How To Fix A P0420 Error Code On Your Vehicle

Remedying the P0420 error code typically requires the replacement of the catalyst. However, some other alternatives can save you money.

Before you begin spending your hard-earned cash, you'll want to verify the P0420 catalytic converter code is present on your vehicle. Have your vehicle scanned by your local auto parts store or repair facility. The auto parts stores typically perform this service free of charge, whereas some repair shops may charge a diagnostic fee.

You'll want to ensure your exhaust system is free of leaks and damage.

Exhaust System Inspection

Start by raising the vehicle via a hoist or jack stand. Never rely on a floor jack to support the vehicle alone, as they are only rated to lift a specific weight, not hold it for prolonged periods. Begin by performing a simple visual inspection. Rusty, worn, or damaged exhaust pipes and connections can cause the surrounding air to dilute exhaust gasses, skewing the oxygen sensor readings.

• Measure back pressure. Back pressure gauges are fairly inexpensive and can be used to diagnose a clogged converter. A converter that is clogged will cause the exhaust to have excessive back pressure.
• Running inspection. It may help to run the engine while inspecting the exhaust. Be mindful that exhaust systems are especially hot and severe burns can occur if your skin contacts the exhaust system. If your exhaust system leaks, you may pick up a hissing sound that can be heard from the leaking areas/connections.

Repair any leaks and drive the vehicle until the catalyst monitor is set.

Catalyst Replacement

Many manufacturers integrate the catalytic converter into either the exhaust manifold or the mid-pipe. Either way, these catalysts are very expensive. Some exhaust specialty shops can weld in a "universal" catalyst; these will work on some vehicles but not all. If you are going the route of having a specialty shop replace the catalyst and not the whole assembly, be sure to verify the emissions requirement of your vehicle. California-spec vehicles must use a replacement that's compliant with the California Air Resources Board (CARB).

How Much Does It Cost To Fix?

Many customers who've been unfortunate enough to see the P0420 or P0430 error code appear on their vehicle will report a hefty repair bill. Usually, the labor cost to replace a catalyst is only a couple of hours on average. The real expense is in the part itself.

The cost of the replacement catalyst will vary from vehicle to vehicle. RepairPal estimates catalytic converter replacement between $2,200 and just over $2,300. We've seen the prices go as high as $3,200 for the integrated catalytic converters. On the Porsche 911, a catalytic converter replacement will go for over $3,200; you'll generally pay more for this part on high-end models.

Alternatively - and much more affordably - catalytic converter fuel additive treatments can cost between $15 and $50. These chemicals are added to your fuel tank.

Additionally, catalytic converters may be covered under special emissions warranties, which can cover some specific emissions components for 96 months or up to 80,000 miles. Check with your dealership to see if your vehicle is covered.

The P0420 error code can sometimes be remedied by using a higher octane fuel or chemical treatments. We recommend attempting some of the cheaper alternatives before pricing a replacement.

Component Cost Estimates