Engine wiring loom: M271.946 engine MERCEDES-BENZ
MERCEDES-BENZ CLC (CL203) CLC 180 Kompressor (203.746)
@user_120666
19.03.2021 20:23
Member
HiÂ
I have suffered from the dreaded oil in wiring loom from camshaft magnets. Unfortunately this only came to light when failing MOT (Lambda sensor). when I looked there was oil dripping out of both Lambda plugs.
I have stripped and located most of the sensor plugs, except for 1 that come off the branch that goes down the back of the engine. There is one that goes under the supercharge to the front of the engine (unidentified) 1 that goes to the supercharge pressure differential sensor, then it goes to the next one which I cannot find, then it goes down to the Lambda sensors(2) and on goes to the bottom of the automatic transmission ( only 2 wire plug). does anyone know where the one I cannot find goes.
19.03.21
08.08.25
- @IsaWill08.08.2025 16:29MemberThe unidentified sensor plug located on the branch that goes down the back of the engine in your Mercedes-Benzâbetween the supercharger pressure differential sensor and the two lambda sensorsâis likely to be one of the following:
- Exhaust Gas Temperature (EGT) sensor or a secondary oxygen sensor sometimes positioned before or after the lambda sensors along the exhaust system wiring loom.
- A boost pressure sensor or a related supercharger/vacuum sensor (other than the main supercharger pressure differential sensor you identified), occasionally mounted underneath or near the supercharger.
- It could also be a knock sensor or a camshaft position sensor wiring connection, as these are often tucked on the back or sides of the engine and can be connected to a similar wiring branch in that area.
Given your reference that after this plug the wiring continues to the lambda sensors and further below to the automatic transmission connector (2-wire), the missing plug is definitely an engine or emission sensor integrated in that loom sequence, typical of Mercedes V6 or supercharged engines.
In Mercedes-Benz engines, the lambda sensor wiring branch often includes sensors such as:
- Upstream and downstream lambda (O2) sensors
- Pressure sensors related to boost or vacuum (other than the main supercharger differential sensor)
- Possibly an exhaust gas temperature sensor located close to or physically integrated with the lambda sensors wiring bundle
Because oil is leaking into the wiring loom from the camshaft magnets, it may also be the camshaft position sensor connector, as these sensors are typically installed near the camshaft housing at the back or top of the engine and connect into the engine loom close to other emission sensors. - @IsaWill08.08.2025 16:30MemberWhat to do next:
- Check the sensor locations on the engine block to see if there is a sensor connector on the rear side of the engine that is unplugged or missing.
- Compare with a Mercedes-Benz wiring diagram or engine sensor location diagram specific for your engine code and year, which will clearly identify each connector in that wiring branch.
- If possible, get a diagnostic tool or wiring schematic (some YouTube tutorials or Mercedes technical sites show detailed wiring and sensor layouts) that can display exact connector locations around the supercharger and rear engine.
Itâs important to identify the exact sensor missing or unplugged to restore wiring integrity and fix the oil contamination issue to avoid further electrical failures.
In summary: The "unidentified" sensor plug in the branch between the supercharger pressure differential sensor and lambda sensors is most likely a camshaft position sensor connector, exhaust gas temperature sensor, or a secondary pressure sensor related to the supercharger or emission system mounted on the back of the engine. Checking a model-specific wiring diagram or sensor layout will confirm this.
