Yeah, maybe i should restate this. On OBD II cars, the OBDII codes are not supposed to clear themselves ever. If the problem is non OBDII, that is not a code the US Gov't says has to appear, also called a proprietary cade, then it CAN go away after awhile, but it doesn't have to. Up to MB then. OBDII codes are the ones that start "PO", other codes start P1 or PI (one of the 2), this is for engines (powertrain, thanks feds). The OBDII codes are the ones the feds say a manufacturer has to have available for scanning by every shop, I am not sure how they know the independents will have a scanner capable of retreiving it. The proprietary codes the manufacturers don't have to supply any of the scanner manufacturers any info about, just the OBDII codes, although some manufacturers end up with alot of proprietary info anyways........Gilly