Why am I getting a "historical" PO171 H DIC code on occasion ?

It suggests at one time the engine ran lean - but I wonder why it triggers the CEL as a historical 171 H code ?

It clears no problem - but curious ?

 

It usually takes 3 occasions of the DTC setting in the computer before the CE light to comes on. If you by chance checked for DTCs say right after the first occasion, you would probably see a H (historical) code, but the CE light would not be on. Sometimes DTCs get set one time and never trigger the CE light, but they are stored as history so you know something is going on.

By the time you see the CE light, it's set the DTC 3 times over a certain period.

 

Confused- so if I get a CEL and the DIC code is PO171H is it, or is it not, a CURRENT or a HISTORICAL event? Understanding that it takes 3 events to trigger a DIC code - but does this by definition result in the CEL light being triggered then by a historical event?


Trying to figure out whether I have a current issue or a current probem.

 

From my experience, the only time you will see a current code is if you do the DTC while the engine is running and the DTC was set during the current drive cycle. In a case like that, you should see "P0171HC". If it was the very first time the code was set, and you checked it on the drive cycle that it occurred on with the engine running, then you'd see P0171C. In this case the CE light would not be on.

If it was set, and you check it anytime the engine is off, you will only see the H code (ie, P10717H).

I've cruised around before with the DIC in DTC check mode before, and have actually seen the code pop-up on the DIC readout.

"Current" means it's going on at the moment in time ... and that can only happen while the engine and computer is active. As soon as you turn the engine & computer off and then back on (ie, cycle it), then that "current" code become a "history" code.

It takes 3 historical events + the one current event to trigger the CE light. If you are cruising down the road, and all of a sudden the CE light comes on, the computer just added the current event to two prior history events.

Hope that makes sense.

Best way to tell it erase ALL codes. Then go drive it for awhile, and then check for and DTCs again. Either check it right after you get home after turning the engine off, or check it while the engine is idling in the driveway.

If there is a C code while checking with the engine running, then it happened during the drive (remember you cleared ALL codes before this drive). If you check it after shutting the engine off, the it will show as a H code, even though it happened during the drive.