The brief
Mr Lawrence dropped by with the car prompting him to top up the engine oil, the kind of nag that means something's not right with either the oil level or the sensor reading it. He brought it in, and while it was in, the battery was due attention too. BMW reads the oil level electronically with a sensor in the sump, and over the years that sensor wears, and on this car it had also started leaking oil from where it seals, which both upsets the reading and loses a bit of oil. A worn, leaking sensor doesn't recover, so it gets replaced. Separately, the battery was getting on for five years old, which is about when they start to fail, so rather than wait for a no-start it made sense to renew it now, with a genuine BMW battery and the registration that a new battery needs.
The diagnosis
We checked the oil first, the level and condition were fine, and the engine oil level sensor was the fault, worn and leaking oil from its seal, which is the top-up prompt. The battery, at close to five years, was on borrowed time and worth replacing before it failed. The rest of the car was sound. So it was an oil level sensor replacement plus a new battery with registration, the false prompt fixed and the battery sorted before it caused trouble.
The work
The oil was drained enough to get at it, the worn oil level sensor removed and a new genuine BMW-spec sensor fitted with a fresh seal, then the oil refilled to the correct level. The old battery was removed and a new genuine BMW battery of the correct type fitted, then registered to the car's power management so the charging strategy is set for a fresh battery. The faults were cleared and the systems checked. A road test confirmed no oil prompt, the dash reading the level correctly, the battery holding charge, and no warning lights.
The outcome
No oil top-up prompt, the dash reading the correct oil level, the sensor sealed and dry, a fresh battery properly registered, and no warning lights. Mr Lawrence got the car back with the nag gone and the battery sorted before it left him stuck. Confirming the oil was good before swapping the sensor meant we fixed the actual fault, and renewing the ageing battery now is far less hassle than a no-start later.
