Volvo 850 » Camshaft Position Sensor

Intermittent cranking without starting can be the most frustrating type of problem to diagnose. The engine camshaft sensor can be a common cause of this type of no start. The camshaft position sensor is referenced at startup by the ECU to determine which valves are open and which are closed and compare that to piston position to fire the injectors and ignition coil at the right time. Typically even intermittent camshaft positions sensor failure will result in a code stored in the ECU so be sure to check the ECU for codes even if you don't have a check engine light on. The camshaft position sensor is located on the back of the exhaust cam and is held on with Torx 40 fasteners.