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skiogawa Posted on May 29, 2014
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Po420 code... there does not seem to be any exhaust leak, and i have replaced all 4 o2 sensors.... only on bank 1, the downstream sensor fluctuates a little more than usual... bank 2 is steady... what could this be? what else can i check? could the heating element in the o2 sensor be at fault?

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sjohnson137

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  • Expert 167 Answers
  • Posted on Jun 10, 2014
sjohnson137
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Joined: May 09, 2009
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2003?

Likely your catalytic converter is stopped up--that's what P0420 is.

Unfortunately, this is a VERY expensive repair unless you do it yourself, and then it's only expensive. You can find a Walker-brand (GM OE for years) replacement on that Amazing store web-site for about $325.00.

At the Chevy store, it's going to cost you TWO THOUSAND dollars, including labor.

You don't have to be a master mechanic to do this. If you know which end of a hammer to hold, I can talk you through it--it just bolts into place (hint: it's called "converter", but it's really 2 of them, pre-assembled into a Y-pipe with all 3 flanges required to bolt it in. It does require some small disassembly of other stuff).

5 Related Answers

Anonymous

  • 1142 Answers
  • Posted on Jun 22, 2008

SOURCE: 2002 GMC Yukon Oxygen sensors

Which sensor are you talking about??

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Anonymous

  • 362 Answers
  • Posted on Jan 28, 2009

SOURCE: o2 sensor bank 2 sensor 2

Bank 2 will the the passenger side or right side and sensor 2 is the O2 sensor behind the catalytic converter.

daves944

Dave C

  • 1050 Answers
  • Posted on May 14, 2009

SOURCE: 02 sensors not ready

The code P0420 indicates that the catalytic converter is not functioning efficiently. This could be because the cat is damaged or the engine is not running very well and the cat cannot keep up with the emissions. You should ensure that the spark plugs and ignition components are in top shape before replacing anything else. If a compression check reveals a low cylinder, you will not be able to prevent this code as even a new cat cannot keep up with a dead miss. If the state of tune and the compression is good, then you'll likely need a cat.

I've posted the drive cycle just so you know what to do when you have resolved the code.

  1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup.
    Do not leave the key in prior to the cold start or the heated oxygen sensor diagnostic may not run.
  2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire, and - if closed loop is achieved- Fuel Trim.
  3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
  4. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
  5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
  6. Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
  7. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
  8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

Anonymous

  • 70 Answers
  • Posted on Dec 02, 2009

SOURCE: CHECK ENGINE LIGHT IS ON, GOT CODES P0157 2 TIMES,

the bank 2 sensor2 is used to check that your catylitic converter is working on that side of the exhaust. without seeing the car and doing sensor tests, it would be a gamble to say replace the sensor. so you can replace it and see what happens or take it to your favorite shop for further diagnosis

c17hydro

Greg Bernett

  • 2993 Answers
  • Posted on Oct 12, 2010

SOURCE: My problem is with Bank

YES! Stop spending the money on this! Get the ECM interrogated.

You have 2 sensors....1 in front of the catalytic converter and one after it.

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2007 Mitsuibishi Eclipse GT
If this is a V6 model, Bank 1 would indicate one side of the motor. Also, if it's the V6 model, I believe there are 3 O2 sensors, one per Bank, and one downstream(post-cat). If it is the V6 model, and it indeed is Bank 1, then just replace the O2 sensor, that's the most likely cause.
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2001 Dodge Stratus R/T o2 Sensor Locations
Yeah, you could do that. Bank 1 is always the engine side where the number 1 cylinder is located. Sensor 1 is the first sensor in the exhaust system, nearest the engine. Sensor 2 is always located farther downstream in the exhaust.
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Jul 23, 2013 • 2001 Dodge Stratus
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Code of PO174 1 system too lean (bank 1) Code PO420 Catalyst efficiency below threshold (bank 1) Code PO430 Catalyst efficiency below threshold (bank 2)

hi,my friend, you can try,

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

Read full answer
Sep 14, 2011 • 2003 GMC Yukon XL
9helpful
2answers

What is engine code P0420
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
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.

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


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 this helps (remember to rate and comment this answer).
Read full answer
Jun 28, 2011 • 2005 Chevrolet Cobalt
0helpful
1answer

My 2000 Cadillac Deville engine light on. Engine code PO420
Catalyst System Efficiency Below Threshold (Bank 1)

A code PO420 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 reading

  • 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
Read full answer
May 11, 2011 • 2000 Cadillac DeVille
1helpful
1answer

03 santa fe code p0421 for warm up catalyst below bank 1is it converter sensors whats bank 1 converter location compared to bank 2 is there 2 banks or converters would it be upstream or downstream if it...
If the engine is a V6 (2.7 or 3.5 lit), bank 1 is next to the firewall (right hand) when facing the back of the engine.
If the engine is a 4 cly (I4), there is only one bank and is designated Bank 1 (exhaust manifold).

The catalyst to which the code refers is the UPSTREAM, and there is only ONE upstream cat for any bank.

Clue: Two upstream O2 sensor and two downstream O2 sensors - one before the CAT and one after the CAT. the downstream O2 sensors are identical to their upstream sisters. The only reason for the DOWNstream sensor is to monitor the CAT efficiency (threshold).

The catalyst on either bank is essentially the exhaust manifold which houses the CAT... it is the only CAT to which the code P0421 applies.

Hope that helped
Read full answer
Feb 06, 2011 • Hyundai Santa Fe Cars & Trucks
10helpful
3answers

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.

Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question
Read full answer
Sep 07, 2010 • 1996 Chevrolet Blazer
1helpful
3answers

Code po430 not sure what maybe converter
One of three (3) possibitlies:
1. Catalytic Converter is malfunctioning.
2. O2 Sensor is malfunctioning. This will be the O2 Sensor located on the Catalytic Converter. However you should check and/or replace both sensors if needed.
3. You have an Exhaust Leak.
In Order of checking:
A. Check and Repair any Exhaust Leak.
B. Replace the O2 Sensor on the Catalytic Converter 1st. Also Known as the Downstream O2 Sensor or HO2 Sensor.
C. Replace the O2 on the Exhaust Manifold prior to the Catalytic Converter. Also Known as the Upstream O2 Sensor.
D. Replace the Catalytic Converter.
Let me know if this helped, or if you have any additional information, problems or questions. Feel free to contact me at FixYa.com!
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Feb 01, 2010 • 1998 Ford Explorer
3helpful
4answers

I have a 2001 MONTECARLO SS it has a Po420 code. Catalyst system efficiency below threshold bank 1. Possible solutions this code is driving me crazy.
Replace Catalytic converter or repair any damage to exhaust system.
Read full answer
Oct 30, 2009 • 2001 Chevrolet Monte Carlo
2helpful
2answers

Showing PO420 and PO304 code
MAP sensor, Maybe, but doubt it.

When the misfire monitor detects a misfire, it will trigger the check engine light with the specific cylinder number as the last digit in the P030X code. For instance cylinder 1 misfire is P0301, cylinder 2 is P0302 etc. In this case we are left with a P0304 in the computer memory. Which is cylinder 4.
Possible Causes:

Fuel injectors, related wiring, sensors and computer issues
Running out of gas, or poor fuel quality
Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
Incorrect Fuel Pressure
EGR system concerns: leaking EGR valve or restricted ports
Base engine concerns: low compression, valve train problems and timing issues
Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiring
Ignition module or related wiring issues
Ignition related sensor faults or wiring issues
This maybe causing PO420 code to go off.
Which is:
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one O2 (oxygen) sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:

Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter
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