Motronic 1.8 was followed by Motronic 4.3-4, which added the ability to perform OBD-II systems fault monitoring. While the Motronic control unit on all of these systems controls ignition timing, it also ensures that the ignition coil is optimally charged, regardless of engine speed. The two knock sensors on the Volvo’s five cylinder engine, along with other sensors, allow the PCM to compute ignition timing for any engine load, temperature, or speed.