Maybe second season. Gus tracked down Mike and followed him using a transmitter in the gas cap. There was that episode where Mike was trying to find it at the junkyard and he pretty much dismantled the whole car before he realized it was inside the gas cap. Pretty sure Mike has used the same transmitters a few times since then.

So when he made a point of removing the gas cap from Jimmy's car that was their way of telling us that Gus and Mike had been following his every move for god knows how long, and they've been pulling more strings with the Lalo stuff than we even knew.