The brief
Nick's 135i came in for a service with the engine check light on, so two things to deal with: the service, and the light. We read it on the BMW handset, but a code is only a starting point, it takes BMW experience to nail the actual fault and avoid replacing parts that aren't the problem. The check light comes on when the air-fuel mixture is irregular, and on a turbo engine that often means air is escaping where it should be going to the engine, a boost or air leak. The turbo pushes pressurised air through hoses to the intercooler and on to the engine, and over the years one of those hoses hardens and splits, so air leaks out, the mixture goes off, and the light comes on. While the car was in for its full safety check, the wiper pump bush turned up faulty as well, so that got dealt with in the same visit.
The diagnosis
The handset showed an irregular air-fuel mixture, and the experienced eye traced it to an air leak from one of the turbo air hoses, split and bleeding air, which is exactly what sets the light on this engine. The full safety check also found the wiper pump bush faulty. The rest of the boost system and the rest of the car were sound. That's a turbo air hose replacement and a new wiper pump bush, plus the service items, rather than throwing parts at a code without knowing the cause.
The work
The split turbo air hose was removed and a new genuine BMW-spec hose fitted with fresh clamps, and the rest of the intake and boost joints checked tight. The faulty wiper pump bush was replaced. The system was leak-tested to confirm it held pressure, the engine check fault cleared and the adaptations reset, and the service items, oil, filters, fluids, done alongside. A road test confirmed the light stayed off, the running steady, the boost clean, the wipers working properly, and the service done.
The outcome
No engine check light, clean boost and steady running, the wipers working properly, fresh oil and filters, and a clean health check. Nick got the 135i back running properly with the light out. Pinning down the actual air leak rather than guessing at a code meant we replaced the hose that was actually faulty, and catching the wiper pump bush during the safety check saved a return trip.
