Greg_Sian said:
I have 96 VS 3.8 exec, had problems starting so i took battery out and cleaned up terminals, now the engine fault light comes on every now and then, checked codes and gave a 12 all ok..... if its on and i turn car off and restart it straight away it goes out? :b:
The way GM have written the code means that just because the CEL comes on it does not mean that the fault code is logged to non-volatile memory so it can be checked later. This means it is possible under certain conditions to get a code 12 (all ok) even if the CEL has been on. There are 3 parts to the CEL and logging of codes...
Current Fault Conditions - What the CEL displays while the engine is running
Logging Filter - To stop very short duration fault conditions from being logged to memory.
History Of Fault Conditions - If the fault occurs for a certain amount of time (see next bit) it is stored here. It is what you get when later extracting fault codes
There are then 4 parts to the filtering of fault conditions....
1) If the CEL was OFF prior to the fault condition and no other faults are in the logging filter then the error must exist for longer than 200mS to set the history fault flag.
2) If the CEL was ON prior to the fault condition and no other faults are in the logging filter then the error must exist for longer than 500mS to set the history fault flag.
3) If the CEL was OFF prior to the fault condition and fault conditions are in the logging filter then the error must exist for longer than 10 seconds to set the history fault flag.
4) If the CEL was ON prior to the fault condition and fault conditions are in the logging filter then the error must exist for longer than 10.5 seconds to set the history fault flag.
No with this information I have 2 theories on why you had a CEL with no faults logged....
1) The fault condition occured very quickly, the CEL was set, the error cleared briefly but was set again and stayed for a few seconds. This means that the CEL would have stayed on for the duration of the error which had to be less than about 10 seconds (using logging filter condition 3) to not log a fault code.
2) An error was logged but for some reason a checksum failed on the non-volatile memory so it was cleared which wipes out the malfunction history amongst other things - the ECU does a check on startup and during normal running and if it finds an error clears everything, this is the same as removing the battery for a bit to reset the ECU.
Clear as mud :thumbsup:
