One of the systems that Subaru has perfected through improved reliability over the years has been its distributorless ignition system (DIS) for all of its models. Because of the horizontally opposed design of its engines, the ignition system can be centrally mounted and made simple.

In this article, we will touch on some common diagnostic tips, as well as the more technical tests of the components in the relationship between the ignition system and related sensors. We'll also provide insight into some of the more frequent failures that we encounter, how we arrive at the diagnosis and make the repair. This article will cover the Legacy series, as well as the later Impreza, Outback and Forester models. The systems are pretty standardized for all of these models, except for pre-1995 models and the 2.5L DOHC engine.

Sensor's Input
The Subaru DIS is fully controlled through the Engine Control Module using inputs from several sensors. Ignition timing is controlled after receiving data from cam and crankshaft sensors, the engine coolant temperature sensor, air flow sensor, throttle position and knock sensors. The ECM analyzes this data and transmits a current off signal to the power transistor to control ignition and timing. On all models, the timing is set at 10° BTDC for starting.

The Legacy (typical) system consists of two ignition coils in a single housing and a power transistor assembly. The power transistor...