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I bought a 1995 ford crown victoria and it passed emissions but engine light went on and it's something with catalytic converter or oxygen sensors. How to figure out which is it

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  • Ford Master
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You'll need a shop manual and a scanner or code reader. A scanner would be better.
You would need to know what the trouble codes are, get the diagnostic charts for the codes, and use the scanner to see the data stream from the sensors. The engine computer uses the O2 sensors to monitor the efficency of the cat and fuel mixture.

Posted on Apr 26, 2015

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Posted on Jan 02, 2017

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wiringlunati
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SOURCE: On my 97 Olds Aurora, I'm having trouble passing

The bank 1 sensor should be the one before the CAT on the side of the engine that includes cylinder #1. If you're not sure which bank that is, look across the heads from the side of the engine (front of the car) The bank with #1 on it will have the head a little (1"-2") more towards the front of the engine. The bank that has the head set back a bit will be #2. When there are sensors after the CAT, they're not oxygen sensors, they're CAT efficiency sensors.

Posted on Nov 25, 2009

Testimonial: "Thank you so much, I found out that my number 2 head is in front. Since the cylinders are labeled 2, 4, 6, and 8 are all on the front. Thanks."

  • 7353 Answers

SOURCE: oxygen sensor for catalytic converter location on

Well theres one ahead of the converer and one behind it, The is no sensor for the "converter"

Posted on Nov 06, 2009

  • 740 Answers

SOURCE: 2001 Toyota Corolla Check Engine Light

You cannot guess with these cars,these vehicles have a lot of sensors and actuators can can go bad at anytime, here is my suggestion take your vehicle and to Auto_zone and have them check the codes, they will be able to tell you what they mean. ITS FREE.. then get back to me if you need more help.

Posted on Dec 23, 2008

nattsss
  • 119 Answers

SOURCE: catalytic converter or oxygen sensors?

i would replace the oxygen sensor first as it is the cheapest and easiest

Posted on Nov 06, 2009

  • 67 Answers

SOURCE: 2001 Honda - New Catalytics & O2 sensors -- new 0420/1739/1456

I would send the car for a smoke test for the emissions leak...Find out where the leak is comming from..Repair it..Reset the codes, then do a drive cycle and see what happens...

Posted on Feb 19, 2010

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1 Answer

Car won't pass emissions after replacing catalytic converter


Did you scan for codes to see if there were any besides the catalytic convertor? Unless she's running leaded gas it shouldn't have to be replaced yearly. Is she using an additive that puts lead into the system? I would also check the wire hareness for the O2 sensors. It's not unusual for them to wear and rub a bare spot in the insulation. This will case a short and give a false reading to the computer. Is there any chance that there is a leak in the exhaust? If air is getting in at a joint or a small pinhole ti will screw up the O2 sensor readings.
Hope this helps.

Jan 22, 2014 | 2000 Chevrolet Malibu

1 Answer

Po420 code want pass


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.

Mar 20, 2012 | 2002 Chevrolet Impala

1 Answer

The check engine light came on on my 2004 Pontiac Vibe 1.8. Code PO420 came up on my code reader "catalyst system efficiency below threshold bank 1. Also on the face of the reader the C (cat monitor)...


My first thought would be the converter considering the codes....which will cause the sensors/heaters and other components to fail or read as being bad... I would call a dealer and make sure there are no recalls on the emissions systems and anything to do with the vehicle..
Also it would be worth your while to scan it with a TECH 2 scanner......You may have one I dont know......But I worked for Buick/Pontiac/GMC for 5 years and TECH 2 was a life saver...
It will tell you everything !! If it is running fine though I would just change the oxygen sensor,
clear the codes,test drive it then check it again.....But if you have no problem with it and hooked it to an emissions analyzer and it showed ok I wouldnt worry....

Mar 02, 2011 | Pontiac Vibe Cars & Trucks

1 Answer

2004 Dodge Ram P0420 code. What could be causing this? My emissions are clean (all were within limits), and I just replaced all 4 oxygen sensors


This code is set when the catalytic converters are operating below tolerable efficiency limits. Basically, your catalytic converters are bad and are in need of replacement. You can have bad converters and still pass emissions, but your computer uses the oxygen sensors to determine how well they are working. If the readings are out of a set tolerance, the check engine light will illuminate and DTC P0420 will set. Clearing the code will turn the light out temporarily, but the next time the test is run, the light will come on again.
Hope this helps.

Oct 20, 2010 | 2004 Dodge Ram 1500

1 Answer

Vehicle code PO 420 how would i repair this.


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.

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.

Hope this helps (remember to rate and comment this).

Sep 23, 2010 | Ford Explorer Cars & Trucks

1 Answer

I have 98 crown vic check engine light was not on in till i went to emission testing code read catylc thershold to low


you will need to take it to an exhaust shop and have the catalytic converters replaced unfortunately

Feb 20, 2010 | 1996 Ford Crown Victoria

2 Answers

Oxygen sensor


There are two one on the exhaust manifold in theengine copartment and the other is on the back side of the catalitc converter some will have one on the front as well.

Jan 08, 2010 | 1997 Ford Crown Victoria

1 Answer

Check engine light-on OBD code's P0420 & P0430


The codes are Catalyst System Efficiency Below Threshold (Bank 1)&(Bank 2).

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
  • 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 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.

Oct 06, 2009 | 1997 Ford Taurus

1 Answer

Engine code p0421


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.

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


To Do list

* 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

Jan 04, 2009 | 2001 Hyundai Sonata

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