U0277 Mercedes C 300 shows up when there's an electrical problem that causes the fuel volume regulator to malfunction and open. It's quite an unusual problem and likely intermittent. There are two wires dedicated for each coil; one is battery feed which usually comes from the distribution center, and the other one for the coil driver circuit from the PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil.
Possible Causes :
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Once located, visually inspect the connectors and wiring. Look for rubbing, scraping, bare wires, worn spots or melted plastic connectors. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector.
Diagnostic trouble code U0277 Mercedes C 300 is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.
Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before U0277 Mercedes C 300.
Fortunately, U0277 Mercedes C 300 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.