A handful of fault codes come up again and again on GTIs — here's what they usually mean, so you're not guessing after a VCDS scan. When someone reads me a code, this is the map in my head.
The usual suspects:
- P0171 / P2178 (lean) — a vacuum leak, the PCV, the purge valve, or a boost leak (Boost Leak Diagnosis).
- P0300 / P0301–P0304 (misfire) — coil packs or plugs first.
- P2015 (intake runner position) — the intake-flap lever.
- P0087 (low rail pressure) — the HPFP (and check the cam follower on a Mk5).
- P0011 / cam-timing — the VVT/cam-adjuster, or a stretched VR6 chain.
- P0442 / P0455 (EVAP leak) — the fuel cap, the purge valve or a canister line.
- ABS / wheel-speed codes — a wheel-speed sensor.
So I scan first, then map the code to its usual cause before spending — most of these point at a cheap, common part. See GTI Fluids Capacities.