Some 2004-08 Subaru models (complete list below) may turn on the Check Engine light and log trouble code P0607 (control module performance malfunction) in PCM memory.
According to Subaru, the illuminated light is often accompanied by fail safe mode, which means the engine will be down on power due to the throttle angle opening being fixed at 6 degrees. When confronted with these symptoms the carmaker's recommendation is to get back to basics and check for things that could cause low voltage issues at the PCM. These would include a weak or defective battery, loose battery terminals, a loose ground at the module case or an open or short in the power and ground circuits to the PCM. After the repair is made, don't forget to wipe out the trouble code from module memory.
Vehicles that can be afflicted by the module woes are 2004-08 Imprezas and Foresters, 2005-08 Legacy and Legacy Outbacks and 2006-07 Tribeca SUVs.