I am posting this inn case it will help someone else avoid the frustration of this problem. My daughter's 2005 E320 started running very rough a couple hours from home, then it was crank no start. All I have for scanning is a Foxwell NT530, and the initial scan showed misfire in cylinder 1. Since I had a couple extra coils with me, I changed cylinder 1 coil. Still crank no start. Hoping to fix it in the parking lot, I went to a local parts store and bought a generic crankshaft position sensor and installed it. Still crank no start. I swapped the fuel pump relay, tested the fuse but still crank no start. I opened up the fuel level sensor to test for voltage, but the slightest pressure snapped off the twenty-year-old plastic nub from the sender to the fuel line. At that point I had it towed home.

After getting it home I ordered and replaced the sender, assuming the car knew the sensor wasn't German, I purchased and installed a Bosch crankshaft position sensor. Still crank no start. Testing the crankshaft signal at the ECU when cranking, I had the appropriate range of voltage (this car still has the two-wire inductive sensor rather then the three wire hall effect sensor), and neither wire show signs of a short, but I thought perhaps the existing wires were degraded, and the signal was not good, so I ran a new pair of wires from the CPS pigtail to the ECU. Still crank no start. I tested the voltage at the sender unit when cranking now and I was getting 12 volts, and replacing the relay with a jumper didn't activate the fuel pump, so I replaced the fuel pump. Still crank no start. I was watching a great diagnostic Youtube channel from DiagnoseDan, and I saw a video where he diagnosed a Peugeot CPS to have the polarity reversed. I thought there is nearly a zero percent chance that a Bosch CPS that is used in thousands of W211 vehicles would have the polarity reversed, but since I spliced a new CPS wire, it was simple to snip, swap and test, and the car started right up. I am still not 100% sure whether the Bosch part is correct, since I ordered it on Amazon, but neither the Bosch CPS nor the generic CPS worked, so I think there was some change in polarity between this W211.

 

After the car started I made it only a mile before it died again. I learned my lesson about buying Bosch parts (or any parts) from Amazon. I figured I must have received a counterfeit or defective Bosch sensor, ordered a new one from FCP Euro, swapped the wires back to the original position, installed the new sensor and the car runs perfectly. I will not order parts from Amazon again...

 

I also learned this the hard way with counterfeit parts. Ordered NGK plugs for two cars and a few months later miss fires. Pulled plugs thinking it can't be that and they where completely wiped out. Huge gap between the electrode and tip from wear like they had 100k of miles.
So, when looking back at the orders you should always look at the "brand" of the item you are buying. Mine said "unknown" and should have said "NGK" and I never caught it. Now I see this all the time with stuff especially when it is VERY cheap compared to normal pricing.