Hello, I’m dealing with a very strange issue involving the left xenon headlight. The car is not driven on a daily basis—only around 200 km (125 miles) per year—and it spends the entire year parked in a garage. Recently, I decided to perform a PCV overhaul following the FCP Euro YouTube video, as the original PCV system (from 2010) was still in place. I also installed new mass‑air‑flow gaskets. No other components were touched. During the same period, I replaced the instrument cluster (monochrome to monochrome, same production year—2010—but with very low mileage) because the original cluster had a failing backlight (flickering, dimming, etc.). I followed a Benz YouTube tutorial to remove the cluster. Again, nothing else was disturbed. After reassembling everything, I connected Xentry and, to my surprise, found three current errors in the left xenon headlight module, as shown in the screenshot below.
left xenon errors

(The “zero position” error now appears as stored because the module currently sees the level‑sensor voltage as 5.0V. On other days, it detects 0V, and then the error becomes current.)

The car is factory‑equipped with Airmatic and ILS, so I checked the wiring diagram for the level sensors. It turns out they are connected to the Airmatic ECU. I scanned the Airmatic ECU for faults—there were none. All four level sensors report correct values (the left side is slightly off in the screenshot because the car was on a jack at the time).
airmatic levels

Next, I suspected the left ballast might be faulty. I installed an OE, very low‑mileage replacement ballast and performed variant coding, but the result was exactly the same. The right xenon headlight has no issues, as shown in the screenshots.
right xenon actual can values
right xenon other actual values

Communication with the left headlight module works perfectly—I can perform variant coding, read faults, etc. However, the left xenon module shows no actual CAN values. What’s even stranger is that there are no warning messages on the dashboard, and the automatic high‑beam assistant works normally.
left xenon actual can values
left xenon other actual values

I am certain this issue did not exist before winter, because I have a saved short test (PDF) showing no faults at that time. The car is 100% factory stock with no aftermarket equipment or modifications. All ECUs have the latest available software (updated in 2024), so software mismatch is not the cause.I also performed a simple resistance check on the CAN line at the left xenon connector, and it shows 60 ohms, which is correct. At this point, I am out of ideas about what could be wrong or what else I can test to track down the issue. I am pretty sure I was careful enough not to pull or pinch any wires. Any help or suggestions would be greatly appreciated.

 

This is a tough one because there are no apparent CAN error messages and you can read/write to the E1n1 unit however the E1n1 unit is not picking up level sensor signals over CAN apparently. What if you started trouble-shooting from "List of Fault Codes" list on E1n1 diagnosis screen. For example, Code 9042 should bring up actual value of B22/8 Left front level sensor "as seen" by E1n1 light control unit. Trouble-shoot from there.

Also perhaps use CAN topology screen to help you. E1n1 on CAN G and A1 Instrument Cluster & N51/3 AIRMATIC ECU both on chassis CAN E. CAN G and CAN E connected by N93 Central Gateway unit. Probably worth trying to disconnect Main Battery (-) for a minute or so and reconnect for a hard reset of all ECU's to clear out any bugs in DRAMs.