Check engine light associated with cruise control use

2007 forester CEL only comes on when using cruise control. Code reads as “small leak”. Smoke test uncovered no leak. Dealer says diagnostic test only runs on cold start with gas tank between 75 per cent & and 25 full. Trip today on full tank CEL on w/i 50 milles. Mechanics say no connection between cruise and emissions. Why the correlation? Dealer suggests cracked pressure sensors on fuel tank. Est cost $700-$800

Does the cruise control function normally? Including when the light comes on? I believe that on Subarus an engine light will disable to cruise control so you need to clarify what is going on.

If you want help with the code then you need to specify exactly what it is in the format “P1234.” I have to assume it is one of the codes for the evap system (either P0442 or P0456). Any time you get one of these, clean the gas cap and the filler neck. Then coat the gas cap’s gasket with a layer of petroleum jelly and reinstall. If that keeps the light away get a new gas cap.

But there are other possibilities - report the code.

If this car is not under warranty, skip the dealer. They have no special knowledge or magic. Find a good, local, independent auto repair shop and ask them to have a look.

The cruise control is probably operated by vacuum. If you have a ‘small leak’ error only when the cruise control is being used, chances are the cruise control module is the source of the leak. A smoke test is only going to find this when the cruise control is being used. Sitting in a garage is not going to let the cruise control module activate and not detect the leak.

A vacuum tester may be able to show a possible leak in the module if it is bench-tested. That’s my only suggestion so far.

There was a TSA/recall concerning the emissions evap control system. Make sure this was done. Better to go directly to to Subaru to find out. The worst thing about these cars is the dealerships.