Mechanics

P0420

2000 Toyota Camry

Computer problem
2000 Toyota Camry 4 cyl Two Wheel Drive Automatic 130000 miles

I saw several messages posted on this issue and wanted to make sure I fully understood what the issue is and the steps to correctly diagnosis and fix the problem.

Check engine light came on. The code that was kicked out was P0420.

The Catalytic converted was replaced about 2 years ago when the car had 90k miles on it.

Can you send me the steps to diagnosis what the problem may be?

Thank you advance for your help. With your help earlier, I fixed code # p0446 (pressure switch valve) on the charcoal canister.
Avatar
Dolemite44149
October 2, 2009.




DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (EXCEPT CALIF. EMISSIONS) Circuit Description ECM compares waveform of heated oxygen sensor located in front of catalytic converter with waveform of heated oxygen sensor located behind converter to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when both oxygen sensors have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:  Defective catalytic converter.  Heated oxygen sensor circuit is open or shorted.  Defective heated oxygen sensor. Diagnostic Aids Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected. Diagnosis & Repair 1. If any other DTCs are displayed, diagnose and repair those DTCs first. If only DTC P0420 is displayed, go to next step. 2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step. 3. Check heated oxygen sensor No. 1. See DTC P0130: HEATED OXYGEN SENSOR NO. 1 CIRCUIT (EXCEPT CALIF. EMISSIONS). If problem exists, repair as necessary. If problem does not exist, go to next step. 4. Check heated oxygen sensor No. 2. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) test. If problem exists, repair as necessary. If problem does not exist, replace catalytic converter. DTC P0420: CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (CALIF. EMISSIONS) NOTE: Heated oxygen sensor No. 1 refers to oxygen sensor closest to engine block. Heated oxygen sensor No. 2 refers to oxygen sensor farthest from engine block. NOTE: For component location, see appropriate illustration in THEORY & OPERATION article. NOTE: For component location, see appropriate illustration in THEORY & Circuit Description ECM monitors heated oxygen sensor No. 2 (located behind converter) to determine if converter performance has deteriorated. If converter is functioning properly, heated oxygen sensor waveform switches back and forth between rich and lean more slowly. DTC is set when A/F sensor and heated oxygen sensor No. 2 have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are:  Defective catalytic converter.  Heated oxygen sensor No. 2 circuit is open or shorted.  Defective heated oxygen sensor No. 2.  Defective Air/Fuel (A/F) sensor.  A/F sensor circuit is open or shorted. Diagnostic Aids Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected. Diagnosis & Repair 1. If any other DTCs are displayed, diagnose and repair those DTCs first. If only DTC P0420 is displayed, go to next step. 2. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step. 3. Check A/F sensor. See DTC P1130: AIR/FUEL SENSOR CIRCUIT RANGE/PERFORMANCE (CALIF. EMISSIONS). If problem exists, repair as necessary. If problem does not exist, go to next step. 4. Check heated oxygen sensor No. 2. See DTC P0136: HEATED OXYGEN SENSOR CIRCUIT (SENSOR NO. 2) test. If problem exists, repair as necessary. If problem does not exist, replace catalytic converter. OPERATION article.
10/3/2009 .
With 130,000 miles you are past the 100,000 mile srvice life of the 02 sensors.

Merlin2021
Oct 3, 2009.
So ended up replace the front O2 sensor. Success.

I could not get my volt meter to get a reading - there wasnt an available spot to plug in the probes.

Thanks again for your help!

Tiny
Dolemite44149
Dec 26, 2009.
Good work! Thanks for the rep points!

Merlin2021
Dec 27, 2009.
OH man!

Merlin, 2 months went buy and the check engine light came on again yesterday. The error code was the same - P0420.

Is it possible the first 02 sensor was just bad? Uggg.

Thanks again for your help.

Greg
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Tiny
Dolemite44149
Mar 4, 2010.
There are two reasons this code comes up, first is the cat is actually bad, second is usually the O2 sensor AFTER the cat, if you have a scanner that reads live data, check the rear sensor, it should show an almost flat line graph, if it switch between high and low like the front sensor, it no good! Replace downstream O2.

Merlin2021
Mar 5, 2010.

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