CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Subaru Forester 2001 -- Check Engine and Sudden bad mileage

My daughter is driving to Texas from Colorado. Check engine light came on, codes to O2 sensor or catalytic converter. She noticed a sudden drop in mileage (fuel economy), but reports no loss of performance. Should she stop to get work done on the possible items from the engine code? Is it urgent?

How was it determined that the mileage dropped?

Yes she should have the CEL addressed. However it can not be assumed that it is an O? sense or converter, based on the CEL alone.

Now about that trip.  I would not want my daughter driving that car that far with any question about it's condition.  If she wants to drive it half a mile to the grocery to buy a turkey today, OK.  The problem is she is already on the highway.  I might tell my daughter to finish the trip with two notes:

Have charged cell phone with her and if the light starts flashing or she experiences drivability issues, to spot where she is at.

CEL code was read at AutoZone and reported as converter or O2 sensor. She noticed that her fuel gauge was at half-empty after driving about 50% fewer miles than normal for using half a tank. She stopped for the night. Should she get this looked at before driving another 500 miles today?

Even though the code indicates a problem with the O2 sensor or catalytic converter area the real problem is most likely with something else. Possibly the fuel pressure regulator or coolant temperature sensor. Either one could cause the fuel to be running rich and cause the code to set. A bad O2 sensor could cause the trouble also. Going too long without fixing the trouble may cause damage to the CAT which is expensive to replace. She should be able to make it to Colorado ok I would think and have the car looked at there.