A BMW engine light, or ‘Service Engine Soon’ light, can be triggered by a variety of problems. One of the most common is ignition coil failure. PCV valves tend to fail, as well, causing the service light to come on. The camshaft position sensor can malfunction which causes the ‘Service Engine Soon’ light to turn on, as well. If the thermostat sticks, which is common, the engine will overheat and trigger the service light. The thermostat can stick in such a way as to cause the engine not to heat up enough. Also, this will trigger the engine warning system too.