P0420 with NO MIL?
#1
P0420 with NO MIL?
2007 Avalanche, LC9 engine. I've had a P0420 code for a long time now. Check Engine/Malfunction Indicator Lamp (MIL) light has been lit for months. It's due for inspection in January so I need to fix it. MIL lit up is an automatic fail. My code scanner tells me the code, as well as the status of the MIL - which is "ON." Today the MIL went out. Did it magically repair itself?
I plugged in the scanner and it still has an active P0420, but the MIL is now "OFF." I don't know what to make of this. The state inspection station plugs into the OBD-II port to check for codes but since the MIL isn't lit I don't know whether it will pass or not.
If I need to do the work, I'd rather do it now than when it's really cold in January.
Has anyone seen this before (P0420 but no MIL)?
I plugged in the scanner and it still has an active P0420, but the MIL is now "OFF." I don't know what to make of this. The state inspection station plugs into the OBD-II port to check for codes but since the MIL isn't lit I don't know whether it will pass or not.
If I need to do the work, I'd rather do it now than when it's really cold in January.
Has anyone seen this before (P0420 but no MIL)?
#2
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Location: Wisconsin
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I take it that they cleared the code when you read them. You may have what's referred to as a pre-code. Try having the codes cleared again and then disconnect the battery for about 10 minutes. After reconnecting the battery, have the computer scanned again for codes and see if the code comes back. In Wisconsin, they look to see how long ago the codes were last cleared. You need to put on about 150 miles in Wisconsin to get the emission test run.
#3
I take it that they cleared the code when you read them. You may have what's referred to as a pre-code. Try having the codes cleared again and then disconnect the battery for about 10 minutes. After reconnecting the battery, have the computer scanned again for codes and see if the code comes back. In Wisconsin, they look to see how long ago the codes were last cleared. You need to put on about 150 miles in Wisconsin to get the emission test run.
#4
the monitor can run and pass; turning off the mil...the code will still be stored in the module....it may need to run and pass a number of times before the module clears it from memory...some parameters require 40 trips before it is cleared from memory; without the use of a scan tool to clear it.
a p0420 is usually due to a tired old cat. Slow switching 02 sensors can cause it also. Installing new rear 02's and having slow switching front 02 sensors can cause the fault also. If the 02 are switching properly, replace the cat. Don't cheap out and put in a cheap cat either. Low cerium content from a cheap cat will cause a immediate reset of the p0420
for the state inspection, no dtc can be present and all i/m monitors must have run and passed.
a p0420 is usually due to a tired old cat. Slow switching 02 sensors can cause it also. Installing new rear 02's and having slow switching front 02 sensors can cause the fault also. If the 02 are switching properly, replace the cat. Don't cheap out and put in a cheap cat either. Low cerium content from a cheap cat will cause a immediate reset of the p0420
for the state inspection, no dtc can be present and all i/m monitors must have run and passed.
#5
the monitor can run and pass; turning off the mil...the code will still be stored in the module....it may need to run and pass a number of times before the module clears it from memory...some parameters require 40 trips before it is cleared from memory; without the use of a scan tool to clear it.
a p0420 is usually due to a tired old cat. Slow switching 02 sensors can cause it also. Installing new rear 02's and having slow switching front 02 sensors can cause the fault also. If the 02 are switching properly, replace the cat. Don't cheap out and put in a cheap cat either. Low cerium content from a cheap cat will cause a immediate reset of the p0420
for the state inspection, no dtc can be present and all i/m monitors must have run and passed.
a p0420 is usually due to a tired old cat. Slow switching 02 sensors can cause it also. Installing new rear 02's and having slow switching front 02 sensors can cause the fault also. If the 02 are switching properly, replace the cat. Don't cheap out and put in a cheap cat either. Low cerium content from a cheap cat will cause a immediate reset of the p0420
for the state inspection, no dtc can be present and all i/m monitors must have run and passed.
NJ lets you get away with one not-ready monitor so long as it's not a catalyst monitor if you've failed for the catalyst previously. I usually go through with a not-ready EVAP monitor because they take for ever to reset. Whatever the conditions for that are, I take a long time to meet them. I very rarely drive on the highway or have the truck above 50 MPH.
#6
the evap monitor is allowed to not complete is some areas...the evap on some makes are temp dependent...the monitor wont run if the temp is to cold. That is why you dont get small evap leak codes in the winter
#7
And now it's developed a pretty solid misfire - but only at idle. Threw a generic P0300 (misfire) code. But that one does not turn on the MIL so it should be okay if it doesn't clear up by inspection time.