Join Date: Jun 2006
Location: Eastern ON Canada
Car: 07 OBW 2.5i D-4AT
Feedback Score: 7 reviews
Probably, but I must ask why disconnect the battery? To clear the CEL?
As the car seemed to be running well enough, the only apparent "problem" is the light being on, and the fact that the cruise control is disabled when the CEL is on.
In this regard, if in the next three drive cycles no faults had been detected (e.g. if the P0028 was a single "event"), the CEL would have gone out on its own and the cruise control restored, while the trouble code itself would have remained in memory for up to 40 drive cycles. This might have been useful for the dealer. Without any codes, the dealer might not have anything to go on.
Is your car still under the power train warranty (5/60k)? If so, then you would want the code(s) there so that it can be recorded on the work order. That way, even if the dealer doesn't find anything, at least there's a "history"; if it happens again slightly after the warranty is past, there might be a case for warranty coverage.
As for the rough idle, when the battery is disconnected, in addition to the trouble codes being erased, the "learned operation" of the ECM and TCM is also erased. (The ECM and TCM monitor how the car is driven and adjust various functions to best meet the driving needs while optimizing fuel consumption and emissions.) When the learned behavior is erased, the controls return to defaults, and it then takes some time to "relearn". There have been reports of "different" or unusual idling in these cases, until a few drive cycles have been completed. (The recommended method to erase codes is to use a code reader/scanner that has this capability. This way, only the stored codes are erased, but the learned operation is retained.)
Perhaps the code and CEL will reappear. If so, leave it for the service department to deal with.