Question about 2000 Toyota 4Runner

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DTC 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.

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 this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Posted on Feb 17, 2012


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SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

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Posted on Jan 02, 2017

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SOURCE: my 2003 toyota matrix has a check engine light

Hello and welcome to FixYa!

Yes indeed. It can be a bad coil. This is common on this car specially if the check engine light doesn't go off after the O2 replacement. Have it replaced and I believe you'll be good.

Hope this helps and thank you for using FixYa! Have a good one!

Posted on May 21, 2011

  • 4803 Answers

SOURCE: using more rpm to maintain

If the RPM is higher at any particular speed than before, the only cause could be that the transmission is slipping. Things like O2 sensors, Catalytic converters, fuel treatments, etc. have absolutely nothing to do with incresed engine (input) speed to axle (output) speed ratios.

Posted on Aug 06, 2011

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My check engine light is on. it is pulling 4 codes P0302 P1670 P0174 P0171

code p 0302 is a misfire on no 2 cylinder
check that the plug lead is on properly, that the lead is operational
move the injector from 2 to another cylinder and see if the misfire follows the move
code p 0174 refers to system too lean bank 2===causes intake /exhaust leak---fuel pressure / pump---injector/s--AIR system--hose connection/s
code p 0171 refers to system too lean bank 1=== causes intake /exhaust leak---AIR system---MAF/VAF sensors---fuel pressure / pump---injector/s -- HO2S
You stated that you replaced the O2 sensor but that is different to the HO2S sensor , does a different job and controls the air/fuel mixture from the ECM
because it has banks 1 and 2 it is a v engine and you will have a HO2S in the exhaust manifold or before the cat converter for each exhaust
O2 sensors are after the cat converter and confirm the HO2S settings for the ECM
to put the lights out , use a scan tool to reset the ECM

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The prevalent cause is the fouling of the O2 sensors in the exhaust pipe and the catalytic convertor(s). This usually caused by the fuel not burning correctly in the combustion chamber. And this can be caused by: bad/no spark in combustion chamber due to weak plugs or electrical going plug coil packs; partially plugged fuel injectors and result being too much un aspirated fuel entering the combustion chamber; bad or old fuel, improper fuel octane for engine.

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Code says #5 is misfiring.

You have 1. A bad injector, which is about to break up and damage your engine or a coil or spark plug wire going bad. Or broke or you have lost compression in that cylinder so first I would do a compression check to see if compression is ok if it is then test the injector and or replace and check for intake leaks around the intake near that cylinder by spraying a small amount of WD 40 around the intake to see if it smoothes out if it does you have an intake leak take it to someone who can do it if your not sure how. and Please rate my answer. thaks Avid101

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1 Answer

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