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Engine light - Code P0420


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I have read that I can use a scanner or oscilloscope to check to see if the O2 sensor is ...


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Old 12-13-2016, 03:21 PM   #1 (permalink)
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Default Engine light - Code P0420
I have read that I can use a scanner or oscilloscope to check to see if the O2 sensor is bad. Is this something an auto repair shop can do, or could my local auto pets store (O'Reilly/AutoZone) could assist with?


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Old 12-13-2016, 04:00 PM   #2 (permalink)
 
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Most auto parts stores can read codes and give you a short printout.


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Old 12-14-2016, 01:42 AM   #3 (permalink)
 
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Originally Posted by cuevrojamez View Post
I have read that I can use a scanner or oscilloscope to check to see if the O2 sensor is bad. Is this something an auto repair shop can do, or could my local auto pets store (O'Reilly/AutoZone) could assist with?
Repair shop can easily scan and fix. OBD II code readers are fairly cheap to buy and would diagnose many P codes.

An O2 sensor is not difficult to switch out depending on its location and wether its siezed. If its siezed a little heat with a torch can free it up usually.


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Old 12-15-2016, 12:12 PM   #4 (permalink)
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Scanner is reading 2 P0420 codes, I assume 1 for the sensor before and 1 sensor after the cat converter. Is there a way to determine which sensor is bad?
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Old 12-15-2016, 03:38 PM   #5 (permalink)
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The P0420 code is typically only for the sensor after the catalytic converter. It is not an "O2 sensor bad" code, it is a catalyst efficiency code which is normally the O2 sensor downstream from the catalytic converter, but it can also be caused by a bad catalytic converter, vacuum leaks, etc.

You can test them with an O-scope. The voltage range should be between .2-.7 volts and if the cat is in good condition, it should stay pretty close to .5 volts after the engine has warmed up fully. You can try to use a voltmeter, but O2 sensors can switch voltage very rapidly and most voltmeters can't read the changes that fast, so it will average them out.
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