When the automobile tech does the diagnostics he should evaluate the codes to find the cause of the light coming on. If he sees a fault he is supposed to investigate the fault to correct it rather than simply clearing the error to extinguish the light. The cars of today run on software. There can be something like a poor contact to a sensor, or a connector is getting water in to it because of degraded insulation causing a false reading, or there could be a part or sensor that is on the edge of failure, and so-on. If there is an intermittent fault then over time it will probably start to become more frequent. If it becomes constant it will be a lot easier to find than when intermittent. There are problems that can happen where something is slightly out of specs, but under normal driving conditions the driver may not notice there is a fault.
