In my 07 impala my engine light is on. both mufflers have big holes in them. will this throw off the oxygen sensors and give me an error reading? when i got it checked it said evap emission ckt check,

Common causes of the P0420 code

• Damaged muffler or leaks in the muffler.
• Damaged exhaust manifold or leaks in the exhaust manifold.
• Damaged exhaust pipe or exhaust pipe leaks.
• A misfire in the engine.
• Oil contamination in catalytic converter.
• Faulty catalytic converter (most common).
• Faulty engine coolant temperature sensor.
• Faulty front oxygen sensor.
• Faulty rear oxygen sensor.
• Damaged oxygen sensor wiring.
• Oxygen sensor wiring that is not properly connected.
• Damaged oxygen sensor connectors
• A leaking fuel injector.
• High fuel pressure.
• Use of the wrong kind of fuel (using leaded fuel instead of unleaded fuel)

P0420 OBD-II Trouble Code Technical Description Catalyst System Efficiency Below Threshold (Bank 1) What does that mean? 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.

Read more at: http://www.obd-codes.com/p0420
Copyright © OBD-Codes.com

that hole is not big enough to relieve the back pressure if your catalytic convertor is restricted.the best way to tell is by using a backpressure gauge installed where the front oxygen sensor is located.pressure should be under 1-2 psi under heavy acceleration.The front oxygen sensor is in the exhaust manifold on the back side of the engine.

this is what i found for you

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 sensorwaveform 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). It is part of the vehicle emissions system.

Most likely, the aftermarket cat they installed is a high flow cat. This commonly causes issues with throwing that code on our cars. You can either have an OE cat installed, or just have the code deleted from the PCM by someone that has a tuner.
Good Luck

Hi there:

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). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:
Leaded fuel was used where unleaded was called for an oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
******** spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings

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 (HO2), replace if necessary
Replace the catalytic converter
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.

Hope helps.

A faulty throttle position sensor or an intake air leak near the mass air flow sensor.

If you have access to a scan tool, check the signal voltage for the Bank 1,3 oxygen sensor with the engine at normal operating temperature. Is it stuck low currently? If so, increase RPM for a few seconds and see if it affects the reading. If it begins working with increased RPM, check for holes in the exhaust near the O2 sensor that may cause a false lean. If the exhaust pipe is intact, the sensor is sluggish, replace it. If the Bank 1,3 O2 sensor voltage reading remains low with increased RPM, unplug it and then observe the reading. It should have increased to about 0.5 volts or thereabouts. If it did, check for water intrusion or other connector problems. If none are found, replace the shorted O2 sensor.

You need to pull the error codes and investigate that indication. REMEMBER, the code is a CLUE, not necessarily the issue...a miss fire often throws an oxygen sensor failure, and the oxygen sensor is often okay, but reading out of spec, as a victim of the missfire.

find a garage with a code reader. This will help you faster. A loose muffler can cause if it is near the oxygen sensors. Other than that just read the codes.

The best advice that I can offer is to have your Engine computer scanned and diagnosed by a qualifed sevice technician and find out why the Engine Computer is turning the light on. If the light is on, it is because the computer has stored one or more fault codes. Fault codes NEVER tell you what parts to replace. They only tell you that one or more of the many systems monitored by the computer is operating outside of its expected "Range" or "Window of Operation". It is up to the person performing diagnosis to test the system that is failing and determine the actual cause of the failure and repair as necessary. You can spend a LOT of money replacing a LOT of parts and NOT fix the problem if proper diagnosis is not performed. Fault codes for the Oxygen sensors are RARELY caused by the Oxygen Sensors themselves. Oxygen Sensors are like informers. When someone within the engine management system is not performing their job, it is the Oxygen Sensor's job to rat them out. Replacing the Oxygen Sensors will only cause the new sensor to tell on the same problem. So, in your case, if you have replaced 3 of the Oxygen Sensors, that means that 6 Oxygen sensor have all been trying to tell you that there is a "Slacker" in the ranks! Stop wasting your money and fire the fool!