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My 1994 imported Subaru Imprezza HX starts fine then as it reaches operating temp the check engine light comes on for between 5 to 30 seconds then goes off. Any ideas?

From the "Ask Jack" archives - 14 December 2009

It's likely the Engine Control Unit is registering an input that is outside of it's recommended parameters for that given operating temperature and engine load.

It illuminates the engine light to alert you that a fault has been detected, even though you may or may not perceive any change in the engine's running.

The only way to determine the root of the problem is to get someone with the correct diagnostic equipment (and knowledge to use it) to check the control unit's fault codes, and carry out a diagnosis on the fault.

They may need to keep the vehicle until they can fault the car first hand.

A Subaru dealer may have a higher charge out rate than a smaller workshop, but their product knowledge and specialist equipment could save time and money with a job of this nature.