Code PO420

Tiny
RIEBE123
  • MEMBER
  • 2000 HONDA ACCORD
  • 3.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 134,000 MILES
I am stumped, I used a scanner to read the code and then erased it two days ago. I figured it would come back since it is low catalyst code which I have been told reappears after two engine cycles if not fixed. To my surprise it didn't come back on, and the car has been driven a lot (totally warmed up). Any ideas why this would happen? Believe me I am happy but confused.
Monday, January 28th, 2019 AT 12:53 PM

3 Replies

Tiny
SEVAG P
  • MECHANIC
  • 405 POSTS
Hello Reibe,

To make sure if your catalytic converter is in good condition run this guide:
DTC P0420: Catalyst System Efficiency Below Threshold

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then recheck for DTC P0420.

P0137, P0138: Secondary HO(2)S (Sensor 2)
P0141: Secondary HO(2)S (Sensor 2) Heater

1. Reset the ECM/PCM.
2. Start the engine. Hold the engine at 3,000 rpm with no load (in park or neutral) until the radiator fan comes on.
3. Except F23A4 SULEV engine: Test-drive at 40 - 55 mph (64 - 88 km/h) for approximately two minutes. Then decelerate for at least three seconds with the throttle completely closed. Then reduce the vehicle speed to 35 mph (56 km/h), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result.

F23A4 SULEV engine: Test-drive at 50 - 55 mph (80 - 88 km/h) for approximately two minutes. Then decelerate for at least four seconds with the throttle completely closed. Then accelerate to 55 mph (88 km/h), and try to hold it until the scan tool indicates FAIL or PASS as the TWC test result.

Is the test result FAIL?

Yes- Check the three way catalytic converter (TWC). If necessary, replace the TWC.

No- Intermittent failure, system is okay at this time.
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Monday, January 28th, 2019 AT 1:14 PM
Tiny
RIEBE123
  • MEMBER
  • 46 POSTS
Thanks.
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Monday, January 28th, 2019 AT 1:25 PM
Tiny
SEVAG P
  • MECHANIC
  • 405 POSTS
You are welcome.
Thank you for using 2CarPros.
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Monday, January 28th, 2019 AT 1:26 PM

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