A 2014 Mercedes-Benz A-Class arrives with a dead right tail lamp, but the diagnostic scanner reads out a list of LIN bus faults and hood sensor errors. The technician noted that the right tail lamp was completely inactive, alongside codes B181E64, U100900, U113E87, and B177687. This scattershot of lighting, battery sensor, and hood switch codes is exactly why we built our diagnostic platform to look at the entire vehicle state at once, rather than treating each code in isolation.
Untangling the LIN Bus 2 Pull-down
The codes U100900 and B177687 point directly to a communication failure on LIN Bus 2. The technician's notes confirmed a malfunction with the left front LED exterior lighting actuation module. Our engine ranked an E1n7 module failure due to moisture ingress as the most likely cause at an 85 percent probability.
On the W176 platform, the E1n7 module sits under the headlamp housing. Condensation drains into the socket, corrodes the pins, and shorts the internal LIN transceiver. This pulls down LIN Bus 2 communication entirely. The required diagnostic step is to inspect the connector pins for green copper oxide and measure the LIN Bus 2 voltage with the module connected versus disconnected to prove if it is dragging the network down.
The Battery Sensor Disconnect
The scanner also pulled U113E87, which flags a missing message from the Intelligent Battery Sensor (B95). Ranked at an 80 percent probability, this typically traces back to physical damage on the 2-pin harness pigtail at the negative battery post. The delicate copper strands inside the wire insulation easily snap when the pigtail is pulled during a battery replacement. Testing this requires a gentle pull test on the two wires entering the IBS plug to detect internal conductor fractures, followed by verifying the 12V power supply.
Explaining the Dead Tail Lamp
The right tail lamp failure was a separate physical issue. Our engine ranked a ground pin overheating failure at a 78 percent probability. On pre-facelift W176 models, all lighting loads in the tail lamp share a single undersized ground wire (terminal 31) at pin 1. High current draw melts the connector housing and burns the terminal, severing the path to chassis ground point W18. The technician needs to unplug the right tail lamp harness and look for melted plastic or black discoloration on the brown ground wire.
The Hood Switch Plausibility Fault
Finally, code B181E64 indicates a signal plausibility failure for the engine hood contact switch (S62/34), ranked at 72 percent. This microswitch inside the front hood latch gets gummed up with dirt and dried grease, preventing a clear signal to the Front SAM. The fix starts with checking switch contact continuity with an ohmmeter in both the open and latched positions.
Mapping the Whole Picture
Instead of chasing electrical ghosts across a CAN network, breaking down these codes reveals four distinct hardware failures that frequently affect this chassis. I would be curious to hear if other independent workshops are seeing this exact cluster of faults in their bays.