P0420 , p0455 how to fix !
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MO Viet Vet
Full Access Member
P0420 code:
This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Ford, GM, etc.
The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it's job is very different from that of a muffler. A catalytic converter's job is to reduce emmissions from the exhaust.
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.
This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a "wear" type item, that is they are not deisgned to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail.
Symptoms
The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle.
Causes
A code P0420 may mean that one or more of the following has happened:
•Leaded fuel was used where unleaded was called for
•A damaged or failed oxygen sensor (HO2S)
•Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
•The engine coolant temperature sensor is not working properly
•Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
•Retarded spark timing
•The oxygen sensors in front and behind the converter are reporting too similar of readings
•Leaking fuel injector or high fuel pressure
•Cylinder misfire
•Oil contamination
Possible Solutions
Some suggested steps for troubleshooting a P0420 error code include:
•Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
•Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
•Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
•Replace the catalytic converter
Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.
We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.
P0455 code:
This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected.
The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
Symptoms
You likely won't notice any drivability problems.
Causes
A code p0455 most likely means one or more of the following has happened:
•A loose or improperly affixed gas cap
•A non-conforming gas cap (i.e. not factory/original brand)
•Other leak or damaged piece in EVAP system
Possible Solutions
With a p0455, the most common repair is to:
•Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
•Otherwise, replace the gas cap, and/or
•Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary
This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Ford, GM, etc.
The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it's job is very different from that of a muffler. A catalytic converter's job is to reduce emmissions from the exhaust.
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.
This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a "wear" type item, that is they are not deisgned to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail.
Symptoms
The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle.
Causes
A code P0420 may mean that one or more of the following has happened:
•Leaded fuel was used where unleaded was called for
•A damaged or failed oxygen sensor (HO2S)
•Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
•The engine coolant temperature sensor is not working properly
•Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
•Retarded spark timing
•The oxygen sensors in front and behind the converter are reporting too similar of readings
•Leaking fuel injector or high fuel pressure
•Cylinder misfire
•Oil contamination
Possible Solutions
Some suggested steps for troubleshooting a P0420 error code include:
•Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
•Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
•Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
•Replace the catalytic converter
Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.
We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.
P0455 code:
This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected.
The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
Symptoms
You likely won't notice any drivability problems.
Causes
A code p0455 most likely means one or more of the following has happened:
•A loose or improperly affixed gas cap
•A non-conforming gas cap (i.e. not factory/original brand)
•Other leak or damaged piece in EVAP system
Possible Solutions
With a p0455, the most common repair is to:
•Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
•Otherwise, replace the gas cap, and/or
•Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary
MO Viet Vet
Full Access Member
MO Viet Vet
Full Access Member
If it was me I would replace all the oxygen sensors if they are old and the same age as they are likely the cause of the P0420 code and hope that the cat(s) are not starting to clog because you say it runs strong and I would replace the gas cap if is old because they do wear out and it is the least expensive to replace and then clear the codes and see if light stays out.
MO Viet Vet
Full Access Member
More than one sensor and have never heard of cleaning them but you do what you want.
MO Viet Vet
Full Access Member
If you have no idea of the age of those sensors and they have at least 60k miles on them, then I recommend replacing all 4 of them. If you want to try and do it cheap then just replace the 2 rear sensors because they are telling you the efficiency of the cat(s). Take it to a tech and have him monitor all 4 sensors to know for sure but if all the same age I recommend all 4 sensors. But I can tell you this for sure. Never heard of cleaning an oxygen sensor and wouldn't know what to clean it with.
MO Viet Vet
Full Access Member
No problem.
