P3084 — Turbo/supercharger bypass valve, bank 2, mechanical failure

P3084 is stored when the ECU sees mechanical fault on the circuit named in the code (bank 2). That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Common causes

The cause is almost always one of a few things. Here they are — P3084 rarely comes from anything outside this list:

• Wear or damage in the moving part itself
• Deposits preventing full travel
• Broken linkage, spring or return mechanism
• Correct electrical command with no mechanical response

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Verify the electrical command is arriving before touching the mechanism
2. Remove and inspect for wear, deposits and free movement
3. Clean and re-test where the design allows it
4. Replace the mechanical assembly if movement is not restored

That is what holds for P3084 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.