Hi, sorry if this is the wrong group to post this

This is regarding the SAE generic DTCs related to misfires and in this case GM vehicles All GM vehicles support the P0300 multi/random misfire, but that is not the case for each cylinder's misfire DTCs of P0301-P0308

As examples shown using an OBD-II scanner where a 2003 Corvette only supports the P0300, but none of the cylinders DTC of P0301 to P0308

[2003 Chevrolet Corvette, ECM/Inputs/Outputs Photo]

Yet a 2005 Corvette you see does support if misfires to any cylinder trips its own DTC

[ECM/Inputs/Outputs Photo]

So questions are,

since these are SAE generic DTCs, were they required by EPA as smog related and if so what year ? If not, when and what models did GM begin having the PCM to have these functional

Is there a SAE /ISO standard, these became required or had been added to a newer year standard ?

It is confusing as an example where a 2002 Caddy Deville had misfires and the owner used a cheap DTC reader, and it reported P0306 (#6 cylinder) Yet a 2004 caddy Deville only reports the P0300 multi/random DTC but will not trip any of the cylinders misfire DTCs

Any rule as to thinking as to GM what years or models had all the misfire DTC group functional to know then when debugging a misfire problem and only P0300 ever trips ?

This than also brings to question, with the tons of cheap DTC readers or hand held scanners out of China that their product do or not be supporting newer DTCs, is there a required standard the vehicle owners should require a tool they buy would include as above the whole group of misfire DTCs as this also would be a problem is the vehicle did not the DTC reader or scanner did not ?

Lastly, since I do custom tuning of GM gas engined vehicles to add to this subject here is a look inside a GM PCM calibration, in part some of the DTCs the tuning tool reports We see here also that

[2003 Chevrolet Corvette, Emissions Photo]

Shows the P0300 DTC but again not each cylinder's misfire DTC

So is there a way to know when a GM vehicle should support this misfire group of DTCs and what to look for if buying a diag tool that they understand and show if any of these DTCs have tripped

Thanks, JR

John Rovner
Owner
Team ZR-1 Corvette Racers llc
Greenville, Texas, USA

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