Monte Carlo Repair Help Have a Monte problem and need help? Good at troubleshooting? Discuss it here!

P0420 CEL was on, but it went away?

  #1  
Old 03-13-2019, 11:25 PM
5 Year Member
3 Year Member1 Year Member
Thread Starter
Join Date: Apr 2010
Posts: 64
Default P0420 CEL was on, but it went away?

Hey guys, keeping this short and sweet.

I had a CEL come on 6 days ago with the code P0420. Did quite a bit of digging and decided this was something I needed to bring my car into the shop for since I have no time or space to check into it. Yesterday morning the CEL went away on the way to work and after driving around 80 miles since then it has yet to come back on. Does it coming on and off help diagnose this for anyone?

Let me know if anyone has any ideas; I'm not sure if this is a real problem or not. Thanks!
 
  #2  
Old 03-16-2019, 08:31 AM
Join Date: Nov 2017
Location: Isanti, MN
Posts: 772
Default

P0420 Catalyst System Efficiency Below Threshold

Causes

A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for (unlikely)
  • A damaged or failed oxygen / O2 sensor
  • Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
  • Failed or underperforming catalytic converter (likely)
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
  • Leaking fuel injector or high fuel pressure
  • Cylinder misfire
  • Oil contamination

Possible Solutions

Some suggested steps for troubleshooting and fixing 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, replace if necessary
  • Replace the catalytic converter
Would be worth getting checked out, hopefully it's something easy. Good luck
 
  #3  
Old 03-17-2019, 07:11 PM
5 Year Member
3 Year Member1 Year Member
Thread Starter
Join Date: Apr 2010
Posts: 64
Default

Thanks for the information! Sure is a lot to take in....the light hasn't came back on yet so I'm going to bookmark this thread just in case it does so I can take appropriate action.
 

Thread Tools
Search this Thread
Advertising
Featured Sponsors
Vendor Directory

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.