Question about 2001 Buick Regal

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False check engine reading - or not

For two years my check engine reading says something like "oxygen below threshold". The auto parts store said it means it is time to replace the catalyic converter. After replacing it, the reading came back. We replaced it again, thinking it was a bad converter, the reading came back. The car does not smell or drive bad, but occassionaly at about 45 mph the rmp will jump and the car will jolt. The local mechanic suggested, from a diagnostic test, the head may be cracked because water is getting in the engine. After spending $1200 and a week in the shop, the light came back on 3 weeks later with the same reading.
What could really be wrong?

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  • purpleforce Jul 27, 2008

    Actually yes, the in the back was changed when the catalitic converter was replaced and the by the engine was replaced before the first one. Maybe the 02 sensors have gone bad.



    I found a recall letter on line that suggests what could have caused the replacement of the catalyic converter in the first place. "this may be due to the front endocne insulation from the catalyitic converter breaking away and blocking the front of the first catalyist brick and preventing the free flow of exhaust gas through the converter.

    This is per a GM notice sent to a person in 2006.



    My car is still running okay. And the light is still on. I will check the O2 sensors and if this suggestion from the GM notice.



    Thank you for you help.

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Have you checked the O2 sensors there are two and they start to go bad around 100000 miles

Posted on Jul 26, 2008

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What means catalyst Efficiency below normal


      Got it scanned and it's P0420: Catalyst efficiency below thresholdbank 1. They said it could be a bad catalytic converter or oxygen sensor. I borrowed a scanner and tried to measure the oxygen sensor readings over time.Sep 8, 2011

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Jan 26, 2016 | Cars & Trucks

1 Answer

My car show me service engine sonn and the scanner say p0431 warm up catalyst efficiency below threshold (bank2) what is this?


P0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2)

Basically this means that the oxygen sensor downstream of the catalytic converter on bank 2 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms: You will likely not notice any drivability problems, although there may be symptoms such as a rough/hard idle when cold.

Causes: A code P0431 may mean that one or more of the following has happened:
* The catalytic converter is no longer functioning properly
* An oxygen sensor is not reading (functioning) properly
* There is an exhaust leak

Possible Solutions: Inspect for exhaust leaks. Next step is to measure the voltage at the oxygen sensor on Bank 2. In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

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 (remember to arte and comment this).

Sep 22, 2010 | Mitsubishi Endeavor Cars & Trucks

3 Answers

My check engine light came the code is p0420


Technical Description

Catalyst System Efficiency Below Threshold (Bank 1)
What does that mean?

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.
Symptoms

You will likely not notice any drivability problems, although there may be symptoms.
Causes

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
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

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 (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.

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Sep 07, 2010 | 1996 Chevrolet Blazer

1 Answer

I have a 2002 Chevy S-10 Crew cab 4wd LS. I was


p0420 is Catalyst System Efficiency Below Threshold (Bank 1) o2 sensors reading are used to check the cat if the cat is plugged you will lose power o2 sensor send a voltage signal to the computer 0 to 1 volts The o2 upstream of the cat should switch back and forth from 0 to 1 volts, average .450v if voltage stays high engine is running rich (low oxygen) if voltage stays low engine is lean (lots of oxygen) cats have a 8-year 80000-mile warranty

Jul 11, 2010 | 2002 Chevrolet S-10

1 Answer

How many oxygen sensors are on a 1999 chevy blazer?i found 3 one on each manifold before the cat and one after the cat. but the guys at the local auto parts store said that there are 4 total. am i missing...


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May 30, 2010 | 1999 Chevrolet Blazer

1 Answer

Check engine light on had obd ll code read. shows p2000 according to auto parts store reader. definition shows for a failed honda catalytic converter?


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Apr 07, 2010 | 2007 Dodge Ram Truck

1 Answer

The engine malfunciton light is on that looks like a motor. Went to autozone for free test code P0420. said could be oxygen sensor, ignition system or couple other things. put in some stp for now. dont...


po420 is catalylic converter system efficiency below threshold, which means converter is not burning or cleaning exhaust good, i ve found that 90% of the time its bad o2 sensors they give off a false reading to computer, replace the frt and rear o2 sensors and reset engine light that should take care of problem, if cat con verter happens to be no good its no loss because new o2s should be replaced with new converter, but i think o2s will solve youe problem. hope this helps.goodluck.

Dec 13, 2009 | 2002 Honda Civic

2 Answers

Catalyst system efficiency below threshhold bank 2


before replacing cat converter replace o2 sensors, they go bad and give a false reading that cat efficiency is below threshold ,meaning converter is no good , i would replace o2 sensors and reset engine light and go from there,the o2 s are normaly the problem, unless you hear cat rattling, well good luck,

Oct 26, 2009 | 2000 Suzuki Grand Vitara

1 Answer

Vsc and check engine light is on . Had it read and code p0420 came up. Autozone said it could be an air leak in exhaust, AF sensor error, fuel system fault or faulty catalytic converter. Is there a cheap...


DTC P0420: Catalyst System Efficiency Below Threashold (Bank 1)

The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, and Air Fuel ratio (A/F) sensor, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Hope this helps :)

Oct 19, 2009 | 2005 Toyota Highlander

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