P0420 Code - Catalyst System Efficiency Below Threshold Bank 1

What Does P0420 Mean?

The purpose of the catalytic converter is to break down harmful pollutants that are created during the combustion cycle. By using fine platinum and gold meshes to filter exhaust fumes, the catalytic converter is able to reduce the emissions expelled from the exhaust pipe.

The catalytic converter has two oxygen sensors. One oxygen sensor is positioned in front (upstream) of the catalytic converter and the other oxygen sensor is positioned at the rear (downstream).

If the upstream oxygen sensor is working properly, its readings should fluctuate from when the car is at operating temperature and when running in a closed loop. If the downstream oxygen sensor is working properly, and there isn't an issue with the catalytic converter, its readings should remain steady.

When the oxygen sensors have readings that are similar to each other, it is an indication that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases, and begins to fluctuate like the upstream oxygen sensor, it means that the oxygen levels are too high and the Powertrain Control Module (PCM) will store the P0420 trouble code.

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What are the common causes of P0420 ?

The most common causes of code P0420 are many and varied, but could include the following-

• Catalytic converter failure due to long use
• Premature failure of rebuilt or refurbished catalytic converters
• Failures and/or malfunctions in almost any system, sensor, or component that affects/controls/monitors/regulates combustion, and therefore, exhaust emissions
• Use of unsuitable or poor quality fuel
• Exhaust leaks in exhaust components such as exhaust manifolds, down pipes, balancing tubes, flexible hoses/pipes, and mufflers
• Restrictions anywhere in the exhaust system that prevents or inhibits the free flow of exhaust gas
• Mechanical issues in the engine, such as excessive wear of cylinders/piston/piston ring/valve gear that cause excessive oil consumption
• Use of enhanced or unauthorized PCM programming
• Unauthorized or illegal exhaust system modifications or alterations
• Failed or failing PCM. Note that in the case of code P0420, this is an exceedingly rare event and the fault MUST be sought elsewhere before any control module is replaced

How do you troubleshoot P0420 ?

With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground. Pack the connector cavity with dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and reassemble.

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