A dead OBDII port can be frustrating when trying to diagnose car problems. This article details how a faulty “Diagnostic Port” fuse can disable the OBDII reader in a Mercedes E500 and how to fix it. This experience highlights the importance of checking this often-overlooked component.
Identifying the Problem: A Missing Fuse
The journey began with a non-functional OBDII reader. Unable to connect a scanner, the search for the root cause started with the vehicle’s fuse box located in the engine bay. However, the engine bay fuse box lacked a diagram for fuse assignments. After searching online forums, the fuse diagram was found tucked away inside the fuse panel on the driver’s side of the dashboard, hidden behind a removable end cap.
Locating the “Diagnostic Port” Fuse
The diagram didn’t immediately reveal the culprit. Initial searches for terms like “ECU Port” and “OBD Port” proved fruitless. A careful, line-by-line examination finally uncovered a listing for “Diagnostic Port.” Cross-referencing this with the fuse box layout pinpointed the exact location and required amperage (15 AMPS in bay 62 for this specific model). Surprisingly, the fuse bay was empty.
The Mystery of the Missing Fuse
The car, purchased nearly new from a Mercedes-Benz dealer and consistently serviced there, had less than 15,000 miles. Previous check engine lights (CEL) had been successfully diagnosed by the dealership using the OBDII port. The only significant event was a recent alternator replacement at a local shop to save on cost. It’s possible the fuse was inadvertently removed during this repair.
The Solution: Installing a New Fuse
A new 15 AMP fuse was installed in the designated “Diagnostic Port” bay. This simple action restored functionality to the OBDII port, allowing for diagnostic scanning. The car, now able to communicate with an OBDII reader, could proceed with its smog check. A pending code from the previous alternator issue remained but was not expected to affect the emissions test.
