P0420 code

trmarshall1 · Apr 13, 2012

I had a friend run a check on my Taco with his code reader and the code was P0420, now that in my opinion would be either an upstream or downstream O2 sensor malfunction. Would it be advisable to replace both sensors at the same time, or determine which one is faulty and just replace that one? Thanks for the help people, I appreciate it.

Casey05Taco · Apr 13, 2012

i do believe just yesterday another 1st gen asked this question. Let me search and see if i can find that thread and maybe the answer will be there

edit: found this.
"
Problem fixed!!
Finally the problem was only an exhaust leak. The flange gasket between the second Cat and the extension, right before the second O2 sensor was finish. I replaced it, erase the codes and voila!! done... the check engine light is off since 2 month now...

The reason the check engine light goes on with P0420 code is because when you are driving at a constant speed, the flow in exhaust creates a vacuum and pull fresh air from exterior by the hole and falls the o2 sensors reading...

Verify leaks by blocking muffler and check for very small leaks, specially near o2 sensors!!"

chris4x4 · Apr 13, 2012

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

Vassily28 · Apr 13, 2012

P0420 Catalyst System Efficiency Below Threshold Bank 1

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P0420 code

#1
trmarshall1 [OP] The Least Interesting Man In The World

#2
Casey05Taco Well-Known Member

#3
chris4x4 With sufficient thrust, pigs fly just fine. Moderator

#4
Vassily28 Well-Known Member

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P0420 code

#1 trmarshall1 [OP] The Least Interesting Man In The World

#2 Casey05Taco Well-Known Member

#3 chris4x4 With sufficient thrust, pigs fly just fine. Moderator

#4 Vassily28 Well-Known Member

Products Discussed in Entire Site Forum: 1st Gen. Tacomas (1995-2004)

#1
trmarshall1 [OP] The Least Interesting Man In The World

#2
Casey05Taco Well-Known Member

#3
chris4x4 With sufficient thrust, pigs fly just fine. Moderator

#4
Vassily28 Well-Known Member

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