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P0420 and P0446 (EVAP vent control and catalyst system)

Tiny
UPDATEAK47
  • MEMBER
  • 2004 LEXUS RX 330
  • 3.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 102,050 MILES
I scanned my car recently when I had check engine and VSC lights on. I got P0420 and P0446 codes with code descriptions catalyst system efficiency below threshold and Evap emission system vent control circuit respectively. I took the car to the mechanic to check, he said the EVAP was okay and the P0420 occurred as a result of bad catalytic converter which I do not want to believe. He did not even check just relying on the code description. I cleared the codes. However, the code P0446 reoccurred after a week.

However, I get this kind of fume smell when the engine is started which I think could be a leak in between the manifold and the catalytic converter.

Could you please help me out with what to do to solve the two codes though I have cleared them out with my scanner, and have not come up again?
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Monday, April 30th, 2018 AT 4:03 AM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

Both will return once the PCM runs its tests on them and they fail again.

Okay, the 420 is a bad catalytic converter. This happens when the rear O2 sensor reads the same as the front O2 sensor. It should be a steady reading. When it is not, then the catalytic converter can no longer process the gases from the engine. It is a simple check you can do by monitoring the 2 O2 sensors.

The 446 is a common code for the vent solenoid. The vent is a normally open system. That means it vents air while fueling. The valve is commanded closed when the PCM does its internal test of the EVAP system. When the system command the solenoid on and the PCM sees nothing on the return circuit, it sets the code.

Roy
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Monday, April 30th, 2018 AT 4:09 AM
Tiny
UPDATEAK47
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Hello Roy, thanks for the quick response. Are you saying the solenoid is bad? What are the expected readings on 02 sensors (bank 1 and bank 2)? From your explanation, I should check my O2 sensors first before working catalytic converter, if I get you clearly?
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Monday, April 30th, 2018 AT 4:38 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
It is possible for the solenoid but needs to be confirmed. An advanced scan tool that can access the EVAP system can command the solenoid on and off. That would be the confirmation.

The front O2 should vary between 0 and 1 volt very quickly.
The rear O2 should be steady at about.475 or.476 volts.

Roy
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Monday, April 30th, 2018 AT 4:43 AM
Tiny
UPDATEAK47
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Thanks so much Roy. I will check and keep you posted. I will as well use advance scanning tool on EVAP to troubleshoot further as recommended.
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Monday, April 30th, 2018 AT 4:52 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Keep me updated.

Roy
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Monday, April 30th, 2018 AT 4:53 AM

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