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P0420: catalytic converter low efficiency code

P0420: catalytic converter low efficiency code 1

P0420: catalytic converter low efficiency code

P0420: catalytic converter low efficiency code

The “Check Engine” indicator is on and error code P0420 has appeared: low efficiency of the catalytic converter system. Does this mean that your converter has already worked out and needs to be replaced? An original catalyst can cost more than $ 1,000, while in the parts market you can pay about $ 300. In any case, such a solution to the problem will cost you dearly, therefore, before changing the converter, make sure that there is a need for replacement.

DTC P 0420 is a common, standard code that is generated when the converter monitor detects a drop in catalytic converter performance. The OBD II system monitors the performance of the catalyst by comparing the signals from the upper and lower oxygen sensors in the exhaust system. The upper oxygen sensor in the exhaust pipe analyzes the composition of the exhaust gases at the engine outlet. The lower sensor, located below or inside the catalytic converter, analyzes the composition of the gases at its output.

Converter monitor self-diagnosis.

The OBD II system converter efficiency monitor conducts a self-test when certain driving conditions occur. Such conditions for the inspection depend on the year of manufacture, model and make of your car. The temperature of the converter and the engine must be working, the engine can idle or at low load and low speed. During this test, the computer temporarily enriches the air-fuel mixture to exhaust the entire supply of oxygen from the converter. The computer then temporarily depletes the air-fuel mixture to determine how long it takes the converter to respond and the lower sensor to change the signal. If the converter reacts too slowly, it means that it is not working effectively enough to reduce the amount of harmful substances in the exhaust gases. In this case, the OBD II system considers the converter faulty, registers error code P 0420 and turns on the “Check Engine” lamp.

Work catalytic catalytic converter

The catalytic converter acts as an afterburner. It oxidizes (burns) any residual fuel vapors (hydrocarbons (HC), carbon monoxide (CO)) in the exhaust gases. The exhaust toxicity level must comply with federal standards, but if a malfunction occurs due to which this level exceeds the federal standards by 1.5 times, the OBD II system detects a malfunction, records an error code and turns on the “Check Engine” indicator.

The OBD II system cannot directly measure the concentration of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gases; instead, it compares the readings of the upper and lower oxygen sensors during the self-diagnosis of the catalyst monitor to determine its performance. If the efficiency falls below the maximum permissible value set by the manufacturer for a particular model, the catalyst will not pass the test and error code P 0420 will be generated..

The switching frequency of the upper oxygen sensor increases, as the engine computer constantly adjusts the fuel mixture from rich to poor and vice versa. At the first start of the engine, the converter is still cold and does not work. At this time, the signals of both oxygen sensors are almost identical, since nothing happens in the converter.

When the temperature of the catalyst reaches about 600 ° Fahrenheit (“300 ° Celsius), it is warm enough to react with exhaust gases. This is the temperature at which the converter reaches its effective operating mode (temperature “l ight off”). After that, he begins to clean the exhaust gases from pollutants. This sharply reduces the switching frequency of the lower oxygen sensor, and its output voltage approaches the average value, which is approximately 0.45 volts.

If in the process of self-diagnosis the monitor of the converter finds out that the converter is operating normally, it means that the vehicle complies with the emission standards and no codes are displayed. But if a decrease in efficiency and a delayed reaction of the converter are detected, error code P 0420 is generated and the “Check Engine” lamp lights up.

The code P 0420 – Does It Mean You Need A New Catalyst?

Yes, as a rule, a replacement is needed – but not always. This code may be false if your monitor is too sensitive. In this regard, some automakers issue technical service bulletins for flashing the engine computer, which should solve the problem of excessive monitor sensitivity.

False error code P 0420 can also be caused by other conditions: exhaust gas leak (which can “trick” oxygen sensors), problems with fuel pressure (too high or too low) or a malfunction of one or more oxygen sensors. But if everything else is normal, and code P 0420 is still present, then the converter does not meet the standards, and therefore, must be replaced so that the car can pass the exhaust gas toxicity test.

In most states, a quick OBD II test is performed with a scanner to check the exhaust gas composition of cars from 1996 and later years of production. Such testing is faster, easier and cheaper than testing the exhaust system in loaded mode on a road simulator or through a dynamometer. According to the rules of most states, for a vehicle to pass OBD II tests with a scanner, it must meet the following criteria: a fully functional OBD II system (the “Check Engine” lamp is operational and the diagnostic connector is connected to the engine computer), the “Check Engine” lamp off, there are no current trouble codes in the computer memory.

Therefore, if the “Check Engine” lamp is on and the code P 0420 (or any other) appears, then the machine will naturally fail the test – unless alternative exhaust testing of the exhaust system for exhaust toxicity is allowed in the state.

If your state still allows alternative testing, and if your machine passes it, then do not worry about the code P 0420. Perhaps your system is too keen to respond to a problem that has not yet appeared.

Causes of converter malfunction

Under normal conditions of use, the effective operation of the original converter is enough for 100,000-150,000 miles. However, anything can accelerate its aging. The most common cause is the contamination of the converter, as the engine burns oil or it has an internal coolant leak (leak through the cylinder head gasket or a crack in the combustion chamber or in the cylinder). Also, the converter may overheat due to misfire, as a result of which unburned fuel enters the exhaust system (check the degree of contamination of the spark plugs and the condition of the wiring to the spark plugs), or due to leakage of compression through a faulty exhaust valve (check compression).

Testing on the level toxicity exhaust

If you live in a state where an alternative test is not allowed, and your car has failed OBD II testing with a scanner, you will have to fix the problem, that is, replace the converter, even if it is still operational, but its efficiency is below maximum.

You can’t just erase the code P 0420 with a scanner to get tested for toxicity. If this is done, the “Check Engine” indicator will turn off, but the car will not be allowed to OBD II testing. To pass the test, the car must run over enough time for all OBD II monitors (including the catalyst monitor) to pass and complete the work cycle without detecting malfunctions. If the monitor of the converter is in “Not Ready” status, you do not have the right to pass the test. And if he completes the cycle and finds the same fault, code P 0420 will be generated again and the “Check Engine” lamp will light up.

So what to do? In nine out of ten cases, you still need to change the converter.

Converter from the manufacturer or from the secondary market?

A catalyst from the spare parts market will cost less (two to three times!) Than the original one. But such converters contain less catalytic substance and the catalyst layer in it is much shorter. Therefore, the warranty is provided only for 2 years or 24,000 miles, and in some cases the operation of such converters is so inefficient that the code P 0420 appears! It is also likely that such a converter will not last until the next test..

If you still decide to buy a converter from the spare parts market, find the one that suits your car (d irect f it) and will sit just as perfectly as the original. Universal converters are suitable for a wider range of models and brands and may be cheaper than direct fit converters, but for their installation, most likely, adapters and / or trimming and fitting of pipes will be required.

Do not waste time installing a used converter, because you cannot know what condition it is in and how many miles it runs. In addition, in some states (for example, California) it’s now illegal to install used converters on vehicles with OBD II..

It is also illegal to remove the converter and install a piece of straight pipe instead, and the OBD II system will still detect its absence.

Worst case scenario: you install a new converter from the secondary market, and after a certain period of driving the “Check Engine” indicator lights up again and error code P 0420 is returned. And now what? Erase the code, drive the car further so that the converter monitor starts working again. If this does not happen, take the vehicle for inspection before returning the error code. Or repeat the diagnosis – you may have missed something, for example, an exhaust gas leak, a problem with the fuel pressure or a malfunction of the oxygen sensor, due to which the monitor receives incorrect readings. You can also remove the converter purchased in the spare parts market and supply the original.

Oxygen sensors

See the Oxygen Sensors article for more information.

If the lower oxygen sensor has defects (the heater circuit does not work, the wiring connector is loose or corroded, the sensor is dirty, etc.), the OBD II system must detect them and generate an oxygen sensor malfunction code. It is these defects, most likely, that interfere with the neutralizer monitor, since it needs good signals from the upper and lower sensors. But sometimes it happens that the oxygen sensor does not function well enough to provoke the appearance of an error code, but is faulty just enough to affect the accuracy of the converter monitor.


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