Catalyst System Efficiency Below Threshold (Bank 1) is a Diagnostic Trouble Code (DTC) or a generic powertrain code. The code means that your vehicle’s computer has detected under-performance from the Bank 1 catalytic converter. The computer monitors the downstream or rear sensor to determine the efficiency of the vehicles’ catalytic converter.
The term Bank is used to identify a specific side of the engine which is a row of cylinders. Bank 1 is always located on the side of the engine with cylinder 1. Cylinder 1 is always located at the front or is the most forward cylinder on the engine. Bank 2 is always located on the opposite side of Bank 1. This applies to inline, V-type, and horizontally opposed engines.
The code is considered generic as it applies to makes of vehicles made after 1996. Although the repairs may differ as per the model such as Subaru, Honda, Ford, Volkswagen, Chevrolet, Toyota, etc.
P0420 OBD-II Trouble Code is the most common besides others like P0442, P0455, P0171, P0300, etc. A catalytic converter is an important part of the vehicle’s exhaust system. It looks like a muffler but its job is very different. It reduces exhaust emissions into the environment.
The catalytic converter has oxygen (O2) sensors in the front and behind. When functioning correctly and the vehicle is running in a closed-loop mode. The waveform reading of the upstream oxygen sensor should fluctuate. While the downstream oxygen sensor reading should be steady. Typically, the P0420 OBD-II Trouble Code triggers Check Engine light when the readings on the two sensors are similar.
These readings and the light are indicative of the converter not functioning efficiently or as per the specifications. There may be other reasons too as Catalytic Converters are not designed to wear out thus do not need replacement. If they fail is it most likely due to something else that caused their failure.
On-Board Diagnostics (OBD) refers to the vehicle’s self-diagnostic capabilities that it reports via screen readings, sounds, lights, etc. The OBD system allows the owner or the technician and access to the vehicle’s sub-systems for status checks and repairs.
OBD-II is an acronym for the second-generation On-Board Diagnostic equipment. It is a standard requirement for light and medium-duty California vehicles. The OBD-II scanner is to a port underneath the dashboard on the driver’s side. They are standardized to any OBD-II scanner and should be able to read the associated codes. The scanner checks for the saved Diagnostic Trouble Codes (DTC) and shows them on the screen.
P0420 code is associated with catalytic converters. Catalytic converters break down the harmful pollutants generated during the combustion cycle. The converter is fitted with gold and platinum mesh to filter the exhaust fumes. The device reduces the emissions released from the exhaust pipe.
Catalytic converters have O2 sensors fitted at the two ends – upstream and downstream. If the two sensors are working properly the upstream sensor should read fluctuations in the O2 concentrations at the car’s operating temperature. The vehicle should be running in a closed loop. On-Board Diagnostics (OBD) refers to the vehicle’s self-diagnostic capabilities that it reports via screen readings, sounds, lights, etc.
The OBD system allows the owner or the technician and access to the vehicle’s sub-systems for status checks and repairs. OBD-II is an acronym for the second-generation On-Board Diagnostic equipment. It is a standard requirement for light and medium-duty California vehicles.
The OBD-II scanner is to a port underneath the dashboard on the driver’s side. They are standardized to any OBD-II scanner and should be able to read the associated codes. The scanner checks for the saved Diagnostic Trouble Codes (DTC) and shows them on the screen. If the catalytic converter is functioning correctly the readings at the downstream sensor should remain steady.
If the readings of both the sensors are similar this indicates that there is a problem. If the voltage in the downstream sensor decreases and fluctuates like the upstream sensor. This indicates that the oxygen levels are very high. The Powertrain Control Module (PCM) will record the P0420 trouble code. The “Check Engine” light will switch on to indicate this issue.
Powertrain Control Module (PCM) is an auto component that functions as a control unit. Usually, it is a combined unit that consists of the Engine Control Unit (ECU) and the Transmission Control Unit (TCU). The Powertrain Control Unit handles more than 100 factors of an automobile. It is an integrated computerized system that controls the automobiles engine, its transmission, and other driveline components.
The P0420 OBD-II Trouble Code is diagnosed using an OBD-II scanner that retrieves the trouble codes stored on the Powertrain Control Module (PCM).
The mechanic studies the live data from the downstream or rear oxygen sensor. The voltage reading from this sensor should be steady. This reading helps determine if this sensor is working properly. If there is a fluctuation the Check Engine light turns on.
The serviceman checks if there are any other codes associated with this problem causing the P0420 code. There may be faulty repairs, misfires due to various reasons and ignition problems. There may be problems with the fuel systems too.
The P0420 code may also be indicated due to damage or wear of the rear oxygen sensor. To diagnose this problem the mechanic may also drive the vehicle while viewing the freeze frame data.
The technician may also check the available updates from the Powertrain Control Module (PCM). These updates may indicate the faults and issues with the catalytic converter. The updates are revises on the Powertrain Control Module (PCM) after the converter is replaced.
The most common mistake during the diagnostics is to replace the Oxygen (O2) sensors before the process is complete. It is prudent to complete the diagnostic to gain a complete picture of the condition of the engine. There may be other components causing the issue that replacing the sensors will not correct.
The vehicle will not show any drivability issues when the P0420 trouble code is displayed. The Check Engine Light will be on but the symptoms of this issue may go unnoticed. But if this problem is not addressed the various components of the vehicle could be damaged seriously.
Even though the issue is not dangerous to the driver the catalytic converter could get badly damaged. The various causes of the P0420 trouble code could be a damaged muffler with leaks in it. The engine may have misfired due to faulty fuel or water in the fuel. It may be due to a retarded spark timing or a cylinder misfire.
A faulty wire, spark plug or fuel injector may cause the cylinders to misfire. This causes the computer to think that it has not injected sufficient fuel. Leading to the injection of extra fuel to compensate which eventually winds up burning in the catalytic converter.
The exhaust manifold may be damaged and may have leaks in it. The catalytic converter may be contaminated with oil or it may be faulty. The exhaust pipe may be damaged or have leaks. The coolant temperature sensor of the engine may be faulty.
There may be issues with the front or rear oxygen sensor. the wiring to the sensors may be damaged or they may not be connected properly. The connectors of the oxygen sensors may be damaged. Or there may be a leak in the fuel injectors or the fuel pressure may be high. Last but not least, you may be using the wrong kind of fuel. You may be using leaded instead of unleaded fuel.
Though there aren’t any noticeable symptoms of the P0420 trouble code the common indicators are;
Illumination of the MIL – The malfunction Indicator Lamp may come on and u may see the following symptoms. If any of the components in the catalytic converter have failed or are broken, they may restrict the flow of exhaust. This leads to a feeling of reduced power output by the vehicle. Call the mechanic to check this using a diagnostic tool. The tool will be able to pinpoint the exact cause of the problem.
No power after the engine warms up – The engine may not run correctly and may not provide sufficient power for acceleration.
The vehicle’s speed may not exceed 30 – 40 mph – You may not notice this issue while driving around residential areas with speed limits. But while on the highway and freeway you may notice the vehicle not picking speed.
The smell of rotten eggs – from the exhaust pipe may be due to Sulphur dioxide. This happens due to insufficient or incorrect amounts of oxygen entering the catalytic converter. This causes an excess of Sulphur collecting in the fuel tank. It causes the exhaust system to emit this odor.
Here are some repairs that can fix the P0420 OBD-II Trouble Code. You can replace the muffler or the leaks in it. Replace the exhaust manifold of repair the leaks in it. Check the exhaust pipe, replace it, or repair the leaks in it.
If you discover issues with the catalytic converter then replace it. You could check the coolant temperature sensor and replace it – if it is damaged. If the front or rear oxygen sensor has issues correct them or replace them.
Check the wirings to the sensors – repair or replace them if they are damaged. Check if the connectors of these sensors are correctly connected. If not repair or replace these connections. If the fuel injectors are damaged or leaking – repair or replace them.
Check and diagnose for misfiring problems and then repair them. There may be other related trouble codes diagnosed by the OBD-II device. These are stored in the Power Control Module (PCM) if the vehicle repairs these issues.
Issues with the fuel system, ignition system, misfires, and air intake systems will damage the catalytic converters in the long run. They should be addressed as soon as possible. Most of the time it is these components that are the cause of the trouble.
If you decide to replace the catalytic converter ensure you are replacing it with an OEM unit. An Original Equipment Manufacturer (OEM) unit is produced by the original manufacturer.
This ensures that you always find the right parts – identical to the ones you are replacing. If you cannot find the OEM part then ensure it is top quality. Not finding the OEM part is usually the reason why the P0420 OBD-II Trouble Code returns.
If this is the case it is recommended you take the vehicle to the manufacturer in the first instance the issue appears. Some certified mechanics are well trained to diagnose and repair these issues.
Here are a few troubleshooting steps to fix the P0420 OBD-II Trouble Code. Check the manifold, catalytic converter, pipes for exhaust leaks. Use a catalytic converter cleaner to remove the build-up in the exhaust system.
Use a scope to diagnose issues with oxygen sensor operations. The oxygen sensor in the front has a fluctuating waveform when functioning correctly. While the rear sensor is more steady. If you don’t see these expected waveforms. Then inspect then downstream or rear sensor it should not be heated.
Usually, you can monitor the temperature of the exhaust from the catalytic converter at the time of revving up the engine and after the engine is fully warmed up. Use an infrared thermometer gun there should be a difference of 100°F between the two readings.
If it is heated then fix or replace damaged oxygen sensors using a special tool. If none of this works then replace your catalytic converter.
The most common mistake the vehicle owners make is they simply replace the oxygen sensor or catalytic converter instead of studying the issues leading to the P0420 OBD-II Trouble Code. It is imperative; you do a proper diagnosis so you do not waste money in replacing the parts unnecessarily.
If you do replace any parts always get them from the Original Equipment Manufacturer (OEM). Another noteworthy point is to get parts with long warranty especially on emission-related parts. Many manufacturers give a 5-year warranty on these parts.