Description
OBD-II Trouble Code Description for P0420 GMC
Catalyst System Efficiency Below Threshold
What does this mean?
OBD2 Code P0420 GM definition:
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 GM code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
Symptoms
Possible sumptoms of OBD code P0420 GM
You will likely not notice any drivability problems, although there may be symptoms.
Causes
Possible causes of OBD code P0420 GM
A code P0420 GM may mean that one or more of the following has happened: Leaded fuel was used where unleaded was called for An oxygen sensor is not reading (functioning) properly The engine coolant temperature sensor is not working properly Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe Retarded spark timing The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible Solutions
Some suggested steps for troubleshooting a P0420 GM 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 (HO2), replace if necessary Replace the catalytic converter One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it’s out of it’s bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It’s worth checking into. See also: P0420 GM.com – P0420 GM Help
The OBD2 Code Information Be Applicable For GMC:
2013 GMC Terrain Denali,2013 GMC Acadia,2011 GMC Sierra All Terrain HD Concept,2010 GMC Terrain,2010 GMC Granite Concept,2009 GMC Sierra Hybrid Crew Cab,2008 GMC Yukon Hybrid,2008 GMC Denali XT Concept,2007 GMC Yukon XL,2007 GMC Yukon Denali,2007 GMC Yukon,2007 GMC Sierra Denali,2007 GMC Sierra Classic,2007 GMC Sierra 3500 HD SLT Crew Cab,2007 GMC Sierra 2500 HD SLT Extended Cab,2007 GMC Sierra,2007 GMC Acadia,2005 GMC Sierra Denali 1500 Crew Cab,2005 GMC Graphyte Concept,2005 GMC Envoy XL Denali,2005 GMC Envoy Denali
Note:
1. The list of automotive Makes at the right edge of the screen. The currently selected ODB-ii codes is for the GMC makes.
2. Look up the other OBD II Trouble Codes, please use the search box. Enter the 5 character trouble codes in the search box and submit the search.
3. Don’t assume a particular OBD-II code means the same for other auto manufacturers as there are many makes specific codes in use.
4. If your OBD-II trouble codes are for a different car, select that vehicle series before searching for the diagnostic codes because not all OBD2 codes used by one manufacture are used by the other makes.
5. The information contained on this site is presented for informational purposes only. We are not responsible for any actions you take on your vehicle. If you have any doubt as to repairs on your vehicle, please contact your technician.