What Is the P0420 Code?
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Seriousness
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The P0420 code signals a low catalyst system efficiency. This code suggests that the oxygen levels are below the desired threshold (Bank 1), which most often results from problems with your car’s exhaust or fuel systems. It can sometimes be tricky to diagnose.
The catalytic converter is a component of the vehicle’s exhaust system. It works by oxidizing the remaining unburned fuel and carbon monoxide (CO) from the combustion process into carbon dioxide (CO2) and water (H2O). It also reduces nitrogen oxides (NOx) into nitrogen.
The converter uses two oxygen sensors – one on the upstream and the other on the downstream. If these sensors show similar readings, something’s wrong. That’s when the Powertrain Control Module (PCM) triggers the P0420 code, causing the check engine light to come on, alerting you that you have a catalyst problem.
Your best course of action is to contact professional help. That way, a trained mechanic will inspect your vehicle and offer solutions to clear the P0420 code.
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What Are the Symptoms of a P0420 Code?
The first and most common symptom of a P0420 code is your check engine light turning on. Second, your engine won’t run as smoothly as it usually does, which could prevent you from going above 30 to 40 mph. This is because of a decrease in the engine’s power output. You might also notice a rotten egg-like smell coming from the exhaust. This also happens when the catalytic converter works overtime or outside of normal driving characteristics.
What Are Some Causes of a P0420 Code?
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
- Misfiring engine
- Catalytic converter oil contamination
- Irregular engine coolant temperature sensor
- A faulty rear or front oxygen sensor
- Oxygen wiring damage
- Loose connection in the O² wiring
- Fuel injector leakage
- High fuel pressure
- Filling your vehicle with the wrong fuel type (i.e., leaded instead of unleaded fuel)
How Serious Is the P0420 Code?
Driving your car with the P0420 code will only lead to further damage to the catalytic converter. Plus, the problem can affect other parts of the car, such as the fuel line and exhaust systems. This is why it’s important to actively monitor your car’s catalytic convertor to avoid other costly repairs. You should consult a qualified technician any time you suspect any catalytic converter damage.
Can I Still Drive with a P0420 Code?
Besides the check engine light blinking, a person may not even notice any significant differences in how a vehicle performs. However, this doesn’t mean you should neglect the issue. Taking your car into a service center to have the issue properly diagnosed by a mechanic would be your best move.
How Easy Is It to Diagnose a P0420 Code?
The most common mistake is to change something before you go through the diagnostics process thoroughly. In this case, replacing the O2 sensors doesn’t mean you’ll get rid of the problem since there might be another component causing your vehicle to signal the P0420 code.
How Difficult Is It to Inspect a P0420 Code?
Before getting started with any repairs, you’ll need to properly diagnose the P0420 code. Most service professionals will use an OBD-II scanner to retrieve the particular code the Power Control Module (PCM) is showing. If the voltage of the downstream oxygen sensor decreases and fluctuates like the upstream oxygen sensor, this is a certain indication that the oxygen levels are too high and the PCM will throw the P0420 code.
However, if there aren’t any visible issues with the upstream and downstream oxygen readings, the mechanic will then check engine misfires, ignition problems and even the fuel system to check for any malfunctions. The mechanic may also check the rear O2 sensor to gauge any excess wear or damage on the part.
An experienced professional will test drive the vehicle and monitor the freeze-frame data. This allows them to determine whether the rear O2 sensor is working properly. Finally, we also suggest updating the PCM to the latest version just in case there’s something wrong with it. It’s not uncommon that an out-of-date PCM is behind your vehicle’s issues.
Need Additional Help with Your P0420 Code?
Even if the P0420 code is causing no noticeable differences in how your car is driving, you should still get it professionally serviced. There’s always a reason as to why the check engine light is coming on. Not fixing the problem can easily lead to more costly engine or exhaust repairs.
Let KBB.com help you find a service center near you. With professional help, you’ll be able to safely use your car whenever you need it.
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