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Autohaus Lake Norman
Under the back seat.
The most common issue for this is a faulty Siren, usually located behind one of the front fender liners. Most Mercedes Benz dealers stock this part because they frequently fail. However, without doing any diagnostics, this is just a guess.
Most of the time, this code is set from a faulty Brake Lamp Switch. However, without doing any type of diagnostics, that is just a guess.
Your vehicle has two knock sensors located under the intake. They check for detonation (spark knock) and adjust spark timing accordingly. MIL Off means that the fault has not failed enough times consecutively to turn the "Check Engine" light on. If you drive it long enough, the light will eventually come on. Most times, these codes set because water collects under the intake manifold and floods the sensor. When I used to see these codes, I would replace both the sensors. The intake manifold has to be removed to gain access to them.
Check valve is located in the fuel pump. If you are loosing fuel pressure when the car is off, its usually either the fuel injectors leaking, or the check valve in the pump is faulty. The best way to diagnose, is to install a fuel pressure gauge and an inline "shut off" valve between the pump and the pressure gauge. This will allow you to stop return flow when the pump shuts off. If it holds pressure with the valve "off", the pump is faulty. If it continues to drop, you probably have a leaking injector. Fuel test kits that include the needed gauge and shut off adapter are usually expensive, so it may be best to take it to a shop.
Tough to say without being able to do any diagnostics on the car, but the first two things I would check, would be the Air Flow Sensor (MAF) and the fuel pump. Both of those can cause loss of power and stalling.
There are many things that can cause an emissions failure, it is important to know what readings were out of spec when it failed. High CO can be caused by faulty MAF sensor, leaking injectors, faulty pressure regulator or bad converter. High HC can be caused by dirty injectors, faulty ignition coils, faulty spark plugs, faulty cam timing solenoids/actuators or bad converter. High NOx can be caused by faulty EGR system (if equipped), engine overheating (or running hotter than normal), faulty cam timing solenoids/actuators or bad converter.
Without scanning the on-board computers for fault codes, it is really hard to say what the problem is. However, the most common failure that makes these lights come on, is the Brake Light Switch. However, this is just a guess.
P1519 has to do with the camshaft timing. This fault code coupled with the noise from under the valve cover, I suspect you have either a failed Variable Timing Actuator (VANOS) or a failed timing chain and/or timing chain guides. When chains/guides fail, most owners and shops opt to replace with used engine, because the front of the motor requires complete tear down (lots of labor) as well as all the parts needed to make the repair makes this a very expensive job. Special tools are also required.
There are many things that could cause that message. Its a generic message to indicate something in the 4WD system has malfunctioned. It could be the transfer case actuator and/or position sensor, it could be the front axle engagement actuator or even something as simple as the selector switch. In order to narrow down the possibilities, it will need to be hooked up to a diagnostic computer, so the fault codes can be retrieved from the Transfer Case Control Module (ATC).