The code came back after a reset — what it means
Clearing a code and fixing the car are different things. How to tell whether the cause is gone.
Write the code down before clearing it
A reset wipes not just the code but everything the unit remembers about it: revs, temperature and load at the moment it happened. Those figures are worth more than the code itself — they tell you whether to chase the fault cold or under load. Save the report before clearing.
Clear it and drive your usual route
Do not idle on the spot: the unit only tests itself in the conditions where the fault lives. You need a drive with a warm-up, some town and some motorway. A code that returns in ten minutes and one that returns in three days are different stories.
Look at readiness, not just the list of codes
An empty fault list right after a reset proves nothing: the unit has not tested itself yet. The readiness screen shows which self-checks have completed. Until they do, «no faults» only means «not looked yet».
Same code again — chase the cause in live data
The same code after an honest drive means the cause is still there. Next you read live data: fuel trims for mixture faults, revs and load for misfires, temperature for cooling. Every code page lists which readings to look at.
A different code came back — that is a hint, not a second fault
Often the second fault explains the first: misfires after a lean mixture, a catalyst code after a long spell of misfiring. Fix the earliest one by time, not the scariest one by name.