OBD code interpretation
Discussion
I know how to read/interpret OBD codes such as P0199 but there are some additional points I don't fully understand.
Codes can be pending (i.e waiting to see if the fault happens again soon). If it doesn't happen again, does the code sit as "pending" for ever, unless deleted?
If that same fault happens again but not for, say, three months will it set a second "pending" code the same as the first? Or just leave the one pending code?
If a code is "current" will the Check Engine lamp always be illuminated?
What makes a code become "historical" and will it be marked as such?
If a code is followed by the letters "FSC" what does that mean?
Any guidance greatly appreciated.
Panamax
Codes can be pending (i.e waiting to see if the fault happens again soon). If it doesn't happen again, does the code sit as "pending" for ever, unless deleted?
If that same fault happens again but not for, say, three months will it set a second "pending" code the same as the first? Or just leave the one pending code?
If a code is "current" will the Check Engine lamp always be illuminated?
What makes a code become "historical" and will it be marked as such?
If a code is followed by the letters "FSC" what does that mean?
Any guidance greatly appreciated.
Panamax
To get the full answer to your questions you probably need to refer to the relevant standards (ISO15031, ISO14229 and SAE J2012) but in summary, for a post 2009 vehicle:
A pending DTC is one which occurs in the current or previous drive cycle. (So after two drive cycles it disappears)
A confirmed DTC is one which has been pending and then crosses the threshold. Depending on severity of the fault with regard to emissions, or not, a DTC will cause a ‘check engine’ caption.
An historic DTC is a confirmed DTC which after (usually five drive cycles) has disappeared.
A permanent DTC is a confirmed one, of a serious nature, which cannot simply be erased on demand, and instead can only be removed after a “Universal Trip Drive Pattern”.
On a compliant vehicle these four status types are made available to the code reader, but it’s up to the device designer how to display them.
I had to look up “FSC” which seems to be a BMW-ism related to coding of certain ECUs i.e. it is not part of the recognised standard for OBD. You're probably best looking on somewhere like MHH Auto for more information on that.
A pending DTC is one which occurs in the current or previous drive cycle. (So after two drive cycles it disappears)
A confirmed DTC is one which has been pending and then crosses the threshold. Depending on severity of the fault with regard to emissions, or not, a DTC will cause a ‘check engine’ caption.
An historic DTC is a confirmed DTC which after (usually five drive cycles) has disappeared.
A permanent DTC is a confirmed one, of a serious nature, which cannot simply be erased on demand, and instead can only be removed after a “Universal Trip Drive Pattern”.
On a compliant vehicle these four status types are made available to the code reader, but it’s up to the device designer how to display them.
I had to look up “FSC” which seems to be a BMW-ism related to coding of certain ECUs i.e. it is not part of the recognised standard for OBD. You're probably best looking on somewhere like MHH Auto for more information on that.
Many thanks Zulu10, that's exactly the guidance I was looking for regarding persistence of codes.
The vehicle in question is a GM car and having contacted the manufacturer of my code reader (which reads GM OEM enhanced codes) they tell me FSC means Fault System Code.
They also said that erasing any code will erase all erasable codes.
The vehicle in question is a GM car and having contacted the manufacturer of my code reader (which reads GM OEM enhanced codes) they tell me FSC means Fault System Code.
They also said that erasing any code will erase all erasable codes.
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