The N20 and N55 engines utilize VANOS variable valve timing systems. These rely on solenoids to adjust the camshafts. A clogged VANOS solenoid (often due to dirty oil) can cause the camshaft timing to be retarded or advanced incorrectly. If the timing is off, the valves open at the wrong time, and combustion fails.

While open flaps prevent overheating, they can cause "over-cooling" in sub-zero temps, preventing your heater from working effectively and increasing engine wear.

This typically involves removing the front bumper to access the unit.