Oil pressure warning light on

This is the most frequent and simplest cause, to check first: there's simply not enough oil left in the sump for the pump to maintain normal pressure. The pump draws oil from the bottom of the sump; if the level is too low, it draws in air at times (especially in corners, under braking, and under acceleration, when the oil sloshes around), and pressure drops, lighting the warning. A low level comes either from an old oil change with oil that's been consumed/evaporated over the miles, from a leak (seal, hose, drain plug), or from internal consumption (rings, valve seals letting oil burn off). The check is immediate and free: with the engine off, the bike perfectly upright, after a few minutes' rest, read the level on the dipstick. If it's low, top up with oil that matches your bike's spec (correct grade, JASO MA/MA2 rating for wet clutches). This is a basic job. But be careful: topping up doesn't excuse you from finding out WHY the level was low (a leak? consumption?), or it'll happen again. And crucially, if after topping up to the correct level the warning light stays on with the engine running, the problem is more serious (filter, sensor, pump): don't ride. The vital reflex: check the level first, but never ride while the warning light is still on.

The oil filter traps impurities and wear particles suspended in the oil. Over the miles, and especially if oil changes are neglected, it fills up and eventually clogs, which restricts oil circulation and drops pressure — hence the warning light. Most filters have a bypass valve that opens once the filter is too clogged, to avoid completely starving the engine of oil, but the oil then passes unfiltered (bad for the engine), and a badly clogged filter or a failed bypass valve lets pressure collapse. This cause is worth considering especially if the last oil change is old. The tell: overdue maintenance (beyond a few thousand kilometers or several months past the recommended interval). Treatment is a basic job: a full oil change with a new filter (which should be replaced at every oil change, precisely to avoid this clogging). Important: respect the filter's torque spec and the correct oil grade. As with all causes of this symptom, if the warning stays on after the fix, you need to investigate further (sensor, pump). Rigorous oil maintenance is the best prevention against this cause.

The warning light is controlled by an oil pressure sensor (switch) screwed into the crankcase: it closes the warning light's circuit when pressure drops below a threshold. As it ages, gets fouled, or short-circuits, this sensor can light the warning WRONGLY, even though actual oil pressure is perfectly normal. This is a possible and rather reassuring cause — but one that must NEVER be assumed without proof, since the same alert also signals a real pressure shortfall (level, filter, pump), which is far more serious and destructive. The absolute rule: before concluding "it's just the sensor," have the actual oil pressure measured with a gauge (connected to the sensor's threaded port). If the measured pressure meets spec, the sensor is indeed the culprit and replacing it is simple (unscrew the old one, fit the new one to torque). If the pressure is genuinely low, do not replace the sensor just to silence the light: the problem is mechanical and serious. This gauge confirmation is intermediate-level and is the heart of the diagnosis. On cost, a sensor is cheap (15 to 50 euros), but the stakes are in not getting it wrong: turning off the light by swapping the sensor while pressure is genuinely low would lead to engine failure. When in doubt, don't ride.

A major oil leak can empty the sump quickly and drop pressure, lighting the warning. Sources: a loose or unscrewed drain plug (even forgotten after an oil change!), a failed gasket (case, cover, a badly fitted filter), a holed oil cooler hose, or a cracked case from an impact. Unlike slow consumption, a big leak leaves obvious oil traces on the ground and on the lower engine, and the level drops fast. This is a cause to spot immediately by inspecting the ground under the bike and the engine block. The tell: a lot of oil on the ground or on the lower engine, and a collapsed dipstick reading. Depending on the source, the fix ranges from simply retightening/replacing the drain plug gasket (basic) to replacing a case/cover gasket (intermediate), or even repairing a cracked case (heavy). In every case, the leak must be stopped first, then the oil topped up to the correct level before restarting. Urgency: as long as the case is leaking and the level is low, do not ride (the engine is running without enough pressure). An underestimated leak can lead to engine failure just as surely as a dead pump: treat it without delay and verify the warning goes out once the level is restored.

Warning: a serious cause (expert-only safety lock). The oil pump, driven by the engine, is the heart of lubrication: it draws oil from the sump through a strainer and pressurizes it to feed the bearings, crankshaft, and camshaft. If it wears out (rotor/gear wear), breaks, or its intake strainer clogs, pressure collapses and the warning light stays on permanently, despite a correct oil level. This is the most feared cause, because without oil pressure, the bearings melt and the engine seizes within minutes. Diagnosis must confirm the pressure drop with a gauge (never assume), and then accessing the pump requires partial engine disassembly: this is a heavy, costly job, rated expert-only, reserved for a professional (tools, disassembly, checking the strainer and bearings, reassembly to torque). The tell: a warning light that stays on while the oil level is correct, the filter is recent, and the sensor is ruled out (actual pressure measured low with a gauge). On budget: the labor for engine disassembly makes this an expensive job, to be weighed against the bike's value (get a quote). Maximum urgency: if the light stays on with a correct oil level, DO NOT RIDE — have it towed. Continuing even a few minutes can destroy the engine.

Repair to be left to a professional.