Question about 1999 Toyota Corolla

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DTC P0420 on 99 Toyota Corolla Which oxygen sensor to replace- before or after the catalytic converter?

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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.

Posted on May 26, 2011

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P 0420 code on toyota corolla2004


Hi there:
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
  • ******** 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

About the possible solutions, some suggested steps for troubleshooting 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.

Hope this helps.

Dec 08, 2012 | 2001 Toyota Corolla

1 Answer

I have a po 420 sensor how can I fix it


this obd2 trouble code table can help you understand the meaning of code, for po420, 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.

Sep 06, 2011 | 2000 Toyota Celica

1 Answer

Where on the 2007 toyota corolla xei can i find the oxygen sensor?


Hi,
There are 2 places.. The first is directly mounted in the exhaust manifold and the other mounted in the first muffler or catalytic converter.

Jan 18, 2011 | 2007 Toyota Corolla

1 Answer

How many oxygen sensors are on a 1996 1.8L toyota carolla? 2 or 3?


Hi:
Your Corolla has 2 oxygen sensors; one before the catalytic converter, and one after!

Oct 06, 2010 | 1996 Toyota Corolla

1 Answer

P0420P


We are assumingn that you are talking about DTC P0420

P0420 OBD-II Trouble Code - 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: Need a catalytic converter? Visit our catalytic converter shopping area for the lowest price on your replacement converter!

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 (remember rated this).

Jul 15, 2010 | 2004 Chevrolet Cavalier

1 Answer

Where is the oxygen sensor located in the 2000 Toyota Corolla?


Depending which O2 sensor it is, it will be located after the exhaust manifold before or after the Catalytic Converter.

Jun 24, 2010 | 2000 Toyota Corolla

3 Answers

I have an engine light on to my Toyota Corolla 2003; diagnosed by the autozone OBD11 SCANNER P420. I replaced the oxygen sensor and the light deleted. After driving the car for 30 miles the light came on...


Hi

The trouble areas associated with this code are as follows:
1)Gas leakage on exhaust system
2)Oxygen sensor
3)Heated oxygen sensor
4)Three–way catalytic converter

The idea is to check for exhaust leaks first then the front sensor and rear sensor. If these all check out then the cat needs to be replaced.

Hope this helps. Thanks for using fixYa

Nov 05, 2009 | 2003 Toyota Corolla

1 Answer

PO420


Not just a faulty catalytic converter will trigger this code. Many other issues can trigger this code.

  • 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
  • Delayed spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible solutions:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter.
  • Replace Coolant Temperature Sensor
  • 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 the catalytic converter
  • Have timing adjusted


Aug 25, 2009 | 2002 Toyota Camry

1 Answer

05 COROLLA P0031


What does that mean? A P0031 DTC (diagnostic trouble code) refers to the O2 sensor (oxygen sensor) located on Bank 1 in front of the catalytic converter. There is also an oxygen sensor behind the converter which is Sensor #2.
This O2 sensor #1 may also be refered to as an air/fuel ratio sensor since on some vehicles it is. It detects the amount of oxygen in the exhaust gas compared to the outside air and then vehicle's computer adjusts the air/fuel ratio going into the engine. The sensor is less effective when the exhaust gas temperature is low, so it includes a heater which is activated to help get better readings from the A/F O2 sensor. Essentially this P0031 code means that the resistance of the heater circuit is lower than normal. In most cases, that resistance level must fall below 0.8 A to trigger the DTC code.
Note, this code is very similar in nature to P0032, P0051, and P0052

Potential Symptoms Most likely you'll not notice any symptoms other than the MIL (malfunction indicator lamp, a.k.a. the check engine light) will illuminate.
Causes A P0031 DTC trouble code may be caused by one or more of the following:
  • A short or open in the heater circuit in the sensor
  • A failed O2 sensor heater
  • Wiring/connectors broken/frayed leading to sensor and/or relay
  • Failed PCM/ECM
Possible Solutions Need an O2 Sensor? Visit our O2 Sensor shopping area for the lowest price on your replacement sensor!
To fix a P0031 DTC code, you'll need to do a proper diagnosis. To do that, you'll want to inspect the wiring and connectors leading to the sensor. Also if equipped with a heater relay and fuse, you'll want to check those as well. Use a digital volt ohm meter to:
  • check for 12 volts at the heater circuit feed (hint: unplug the sensor and check at the wiring connector to do this measurement)
  • check the ground circuit for continuity
  • measure the resistance of the heater circuit (done on the sensor itself)
  • measure the resistance and voltage of the wiring
Refer to a service manual for the correct specifications (volts, ohms) for your vehicle. On some Toyota vehicles this code is triggered when the resistance of the heater circuit is below 0.8 A.
With that said, a common fix for this DTC is to replace the air/fuel (O2 oxygen) sensor #1 on bank 1.
Please keep in mind that OEM (original equipment) replacement sensors are recommended (from the dealer). Aftermarket sensors can be less reliable and of poorer quality (not always, but more often). There's also a chance that replacement parts for the P0031 code may also fall under a federal emissions warranty (check with your dealer to see if it's covered).

Aug 20, 2009 | 2006 Toyota Corolla

4 Answers

2001 toyota corolla check engine light is on. Code reads P420 low threshold. Changed front and rear Oxygen sensors reset the light and drove the car 50 miles and the light came back on. the car will not...


Mass Air Flow sensor! Just remove your air filter cover. Go to Auto Zone and purchase some solvent. Spray past the air filter and it should correct the problem. If not, replace the Mass air-flow sensor. This is commonly mistaken for an oxygen sensor. Mine did this and I followed these steps and it fixed the light. BTW, the light stayed on for 5 years before I fixed it. Never hurt anything. It's normally something to do with emissions. Dummy lights. :)

Aug 06, 2008 | 2000 Toyota Corolla

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