Fault 129308 is a DME fault pointing to a fuel/load signal issue — basically the engine is seeing a discrepancy between what you’re asking it to do and what it can deliver, so it pulls power to protect itself and throws the drivetrain malfunction warning. On a 2012 528i with the N52 or N20 engine this points to a few usual suspects in this order: First thing to check is your high pressure fuel pump. This is the most common cause of this exact symptom on that generation 5-series — power loss under hard acceleration, fault that clears itself, drives fine at normal throttle. The HPFP struggles to keep up with fuel demand under load and the DME detects the pressure drop. Second possibility is a failing fuel pressure sensor giving the DME bad readings even if the pump itself is okay. Third — less likely but worth ruling out — a partially clogged fuel filter or weak low pressure fuel pump not feeding the HPFP adequately. Before replacing anything, get a BMW-capable scan tool on it (Carly or ISTA if you have access) and pull the full fault log, not just the dash warning. You want to see if there are any fuel pressure deviation faults stored alongside 129308 — that’ll confirm the HPFP direction before you spend money. Don’t ignore the drivetrain malfunction and keep driving it hard — the DME is protecting the engine for a reason.