Do our Trucks store error codes?

[Diggerdan11]

So I have an 07 Denali and about a month ago I had a couple codes pop up P0171 and P0174 System Too Lean. I cleared the code, and I have not had an issue since.

I use to get the P0171 code all the time on previous Silverados, but it was usually caused by oil from the after market air filters getting on the MAF, I would just clean it and I would not get the code again until usually the next time I put oil on the filters. When the light came on my Denali I was passing a semi going up a steep hill so I had it floored, so it is possible that it could be a fuel system issue or an air leak issue since I have a stock filter on my Denali.

Anyway like I said I cleared the code, and have not had an issue. Well I went to AAMCO to have them do a quick check on my Transmission (I have 126k and as far as i know it has never been serviced) and they told me that I had the P0171 and P0174 code, yet I dont have a light on my dash. So I am trying to figure out why they said I had those codes, yet the car did not tell me.

So Do our trucks store error codes? Maybe the code readers they use can detect cleared codes? I know that my BMW stores everything, and anytime a code pops up and its cleared it is stored in the computer for future reference? I did not think the GM was that advanced with there computer systems on there cars.

 

[drakon543]

That has been a thing on most obd2 vehicles for a while. So to answer your question yes they do store the codes however thier tech is probably just a moron and was reading any recent codes not realizing they were cleared. While your driving the vehicle does regular checks on its system. Once the code is cleared they will stay in the log but the computer will now assume everything is fine. They might reappear if your in a similar situation and the computer reads a similar error however if they have been cleared and your check engine light is off you currently do not have those codes active.

 

[drakon543]

On a side note even without an aftermarket air filter or intake your maf should still be cleaned with the appropriate maf cleaner once in a while.

 

[Diggerdan11]

That has been a thing on most obd2 vehicles for a while. So to answer your question yes they do store the codes however thier tech is probably just a moron and was reading any recent codes not realizing they were cleared. While your driving the vehicle does regular checks on its system. Once the code is cleared they will stay in the log but the computer will now assume everything is fine. They might reappear if your in a similar situation and the computer reads a similar error however if they have been cleared and your check engine light is off you currently do not have those codes active.

Good to know. I had no idea it's stored the codes.

Either the mechanic is an idiot and was reading an old code, or they knew it was an old code and we're hoping I would pay them hundreds of dollars to "fix" the issue.

 

[MichaelSE]

Anyone know if the trucks store 4x4 error codes also? Or just standard OBDII?

 

[Gurrzt]

On a side note even without an aftermarket air filter or intake your maf should still be cleaned with the appropriate maf cleaner once in a while.

+1 on this, getting ready for a road trip, and was watching minor surging of rpm's @ the stop light, removed the MAF (@ 51k) and cleaned it with MAF cleaner (not brake) reinstalled, and no more surging of rpm. I found that the MAF "ribbons" had some gunk on them.

 

[fiatdale]

Anyone know if the trucks store 4x4 error codes also? Or just standard OBDII?

They store codes from all over. 4x4 codes, AC codes, window switch codes, etc. Only way to read them is not with your standard over the counter OBD2 reader but a more specialized tool like a Tech 2 or Snap on scanner.