Question about 2007 Toyota Corolla

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2001 Toyota Corolla Check Engine Light

I have changed spark plugs(irridium), battery, MAF Sensor, both oxygen sensors, catalytic converter but the check engine light keeps coming on. I passed emission for 2008 after getting the work done. However, the light keeps coming on.

HELP!!

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  • Anonymous Dec 29, 2008

    Autozone says P420. But the Cat is new. Could it be something else instead?

  • Toyota Ed May 11, 2010

    Do you have the codes, the reasons for the light being on? That information will be invaluable for me to assist you properly. Thanks.

  • Anonymous Mar 15, 2014

    i have a 2001 Toyota corolla which the Motor was changed, on test driving it, i noticed the check engine light was on with check engine code p0171, my mechanic check it and recommended we change the MAF sensor, after changing it, the check engine still came back on, to cut the story short, l have changed the O2 sensor, coolant temperature sensor, spark plugs, intake gasket and the problem is still there. The car starts and drives good except the check engine light. What do i do next.

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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

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Disconected Battery and wait about 5 min if when hooked back up if light comes on again I would look at something got unpluged while that other work was going on!!

Posted on Dec 23, 2008

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1 Answer

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

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


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.

May 26, 2011 | 1999 Toyota Corolla

1 Answer

I have a Toyota Corolla/91 1.6 L 4 cyl. DX When I start the car run but does not has power. I changed or replaced the fuel filter, air filter, sparks plug, check up the battery, alternator, fuel...


Check that the ignition timing is set correctly. Use a timing light and set the timing to 10 deg Before Top Dead Center (BTDC). Check the fuel pump pressure output. If you still lack power, it could be that the exhaust system is restricted.

One test you can do is to remove the oxygen sensor. With the sensor removed, start and run the car. The exhaust will be loud with the sensor removed, but see if the engine's power is improved. If it has greatly improved power, the exhaust pipe has a restriction. A very common restriction is that the catalytic converter is internally damaged. Changing the catalytic converter will be necessary if this is the problem. The internal honeycomb of the converter can melt down and turn to **** or it can break down into a coarse sandy substance that can clog the converter exit.

Apr 01, 2011 | 1991 Toyota Corolla

1 Answer

The light Check engine is ON


Here are some very common causes for the engine light to com on.

1. Low fluids, make sure all of your fluid levels are where they should be, particularly the oil.

2. MAF, ( mass air flow ) sensor. This controls the fuel/air mix ratio to the engine.

3. Oxygen sensor, there are 2, ( front means before the catalytic converter, back means after the catalytic converter ) The front measure fuel/air mix, the back measure the emmisions from the fuel/air mix and tells the computer what adjustments need to be made to the fuel/air mix ratio.

I hope this helps you.

Feb 02, 2011 | 2007 Toyota Corolla

1 Answer

2002 Toyota Rav4....check engine light""is


Here are two of the most common causes of the check engine light.

Most common, MAF ( mass air flow ), sensor. A faulty MAF prevents the computer from determining the correct fuel/air mix ratio.

Oxygen sensor. ( front and rear, front meaning before the catalytic converter, rear meaning after the catalitic converter. The front measures the fuel/air mix being sent through the catalitic converter, the back measures the emmisions and lets the computer know if any fuel/air mix ratios need to be adjusted. Both of these can trigger the check engine light.

I hope this helps you.

Feb 02, 2011 | 2002 Toyota RAV4

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

3 Answers

2001 Toyota corolla hesitates on acceleration


Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust).

Mar 27, 2009 | 2001 Toyota Corolla

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

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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