Why does the P0420 code keep coming on and off? (2024)

Why does the P0420 code keep coming on and off?

This is most likely why the check engine light turns off “on its own”. Unfortunately the P0420 code can be several different things from loose or bad sensor connections, exhaust leak , bad o2 sensors or the catalytic converter. If your car is using oil it can also set off the p0420 code.

Why does the P0420 keep coming back?

The most common cause of a P0420 code is a faulty catalytic converter. The following are some other potential causes: Exhaust manifold damage or leakage. Exhaust pipe damage or leakage.

What does a permanent P0420 code mean?

A common emissions code seen in the field, a P0420 trouble code indicates that the catalytic converter isn't functioning efficiently. To work at peak efficiency, the emissions or feed gases entering the catalytic converter need to be perfectly balanced and not excessively elevated.

Can a dirty air filter cause a P0420 code?

A blocked air filter will reduce the volume of air flow, making that code, so the answer is, very probably it is the cause.

How long can you drive with P0420 code?

In general, you can still drive your vehicle with a P0420 code, but you should only do so if necessary. Before further diagnosis, the exact origin of the issue is unknown and by driving with the code for prolonged periods of time, you are risking extensive damage to your engine and exhaust system.

Why do I still get P0420 after replacing catalytic converter?

The error code P0420 does not necessarily mean that your catalytic converter is done for. This indicates a problem, not complete failure of the part. The catalytic converter has two oxygen sensors.

Can wrong spark plugs cause P0420?

Can bad spark plugs cause P0420? P0420 means a catalytic converter problem affecting its efficiency or a problem with the oxygen sensors. So yes, it could be a bad plug which is allowing unburnt fuel to enter the cat and eventually damaging it.

Is it OK to drive with P0420?

A P0420 code is a serious one. Although it will not cause an immediate safety issue, it can indirectly damage your engine if you ignore it for too long. As soon as it is safe to stop, you should not drive your vehicle any further.

Which O2 sensor throws a P0420 code?

A catalyst monitor uses signals from the downstream O2 sensor to determine catalyst efficiency. It uses signals from the upstream O2 sensor as a reference point. If any or both of these oxygen sensors fail, they can trigger the P0420 code.

Should a P0420 code be fixed immediately?

P0420 is mostly a lose fuel cap or a bad seal on the fuel cap or filling gas with the engine running. This should be addressed but not a serious issue. If these issues are remedied you may have an issue with your catalytic converter. This could cause harm to the engine if not fixed.

Can a bad O2 sensor cause a P0420 code?

A bad downstream sensor will usually set some other code(s) specific to the sensor, and may or may not set a P0420. The test requires driving at steady cruise between 55-65 mph and monitoring the upstream and downstream Oxygen sensors. Downstream should be almost flat line if convertor is working.

How much does it cost to fix a P0420 code?

Estimated Cost of Repair for a P0420 Code

A catalytic converter replacement starts around $2,000, O2 sensor replacement can cost $150 to $500.

Can a clogged muffler cause P0420?

Yes, a bad muffler can potentially cause a P0420 trouble code. The P0420 code is related to the efficiency of the catalytic converter. If the muffler is damaged or clogged, it can affect the exhaust flow and lead to issues with the catalytic converter, triggering the P0420 code.

How do you know if your catalytic converter is bad?

If you're experiencing a slow engine ability, lowered acceleration, a smell of rotten eggs or sulfur from the exhaust, dark exhaust smoke, or extreme heat coming from under the vehicle, they are symptoms of a clogged Catalytic Converter, and it should get replaced soon.

How far do you have to drive to reset catalytic converter?

Drive cycles vary by manufacturer and can be reset in as little as 20 miles by a qualified technician (like us) since we have the knowledge and experience but if the normal everyday driver just drives 75-100 miles like they normally would (a mix of highway and city driving) the drive cycle can be completed.

Can a bad O2 sensor cause P0420?

Oxygen sensors are only a part of a greater system, meaning if the p0420 code (or p0141, or p0135) is thrown, that doesn't necessarily indicate the oxygen sensors need replacement. Rather, there could be something else in that system does that's causing the oxygen sensors to appear faulty.

Can an intake leak cause P0420?

The P0420 code indicates a catalyst system efficiency below threshold. Both of these codes can be related to intake manifold and throttle body gasket leaks, which can result in unmetered air entering the engine.

How do you clean a catalytic converter without removing it?

Pressure washing: You can also try using a pressure washer to spray water through the inside of the cat to remove stubborn deposits, but make sure that the pressure washer's setting is at its lowest to avoid damage to the catalytic converter's internal structure.

Is P0420 always a bad cat?

The P0420 diagnostic trouble code (DTC) typically indicates a problem with the catalytic converter, but it's not always the catalytic converter itself that is faulty. The code can be triggered by a variety of issues, such as a failing oxygen sensor, exhaust leaks, or engine misfires.

Why is my new 02 sensor still getting a code?

If you changed the o2 sensor and cleared the code and it came back, then it could possibly be a bad o2 sensor again, maybe the wrong one was changed, maybe you have an issue with your exhaust or catalytic converter. You have to use a scan tool and see what the code is.

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