Why does the BMW 5 Series not respond when starting after wading through water and shifting to neutral?
2 Answers
BMW 5 Series not responding when starting after wading through water and shifting to neutral is caused by water entering the engine, leading to circuit failure. Engine water ingress situations: Generally, engine water ingress can be categorized into three scenarios. The first is engine submersion, which does not damage critical components. The second is minor water ingress, where the engine can still start normally. The third is significant water ingress into the engine cylinders, preventing normal engine startup. Different levels of water ingress will manifest different symptoms in the engine. Precautions after engine water ingress: Do not restart the engine after stalling. Automotive maintenance experts warn that during heavy rainfall, many roads may have deep water accumulation, and drivers should be cautious about the depth of standing water. If the water depth exceeds 20 cm (some high-clearance vehicles like SUVs can handle up to 30 cm of water), avoid driving through it. This is especially true for older models, where lower intake and exhaust ports can allow water to be sucked back into the engine through the exhaust pipe, causing stalling. When driving through waterlogged roads, use a low gear and proceed slowly. A crucial reminder: never lift off the accelerator when crossing water, as doing so creates strong suction in the exhaust system, potentially drawing water back into the engine.
I've been driving for over a decade and often encounter post-flooding malfunctions. When a BMW 5 Series fails to start, common causes include sensor short circuits or ECU damage after water exposure. When water levels rise, the crankshaft position sensor under the car may get flooded, causing signal failure and making the engine misjudge its position during startup. Water-induced short circuits at wiring connectors can also cut off current, with blown fuses being a frequent occurrence. I recommend immediately checking the dashboard fuse box for start-related fuses—replace any blown ones. But avoid forcing ignition to prevent circuit damage. BMW's electronic systems are precision-engineered; water exposure exceeding 30cm can cause issues. Have it towed to a service station for diagnostic equipment checks—DIY repairs are risky and could cost thousands. Always drive slowly through puddles, detour around deep water, and prioritize safety.
