You start the ski one morning and the check engine indicator is on. You shut down, restart a couple of times over the weekend, and by Sunday it is gone. This happens on all the Yamaha four-strokes, from the 2002 FX140 up to the 2024 1.9-litre models, and owners report it often enough that it is worth knowing what it means and what it does not.
What the light going out actually tells you
It tells you that on the last few runs the control unit did not see the problem. In forum reports the indicator is commonly said to reset itself after several start and stop cycles. That fits a fault that is not constant: a connector that makes contact on some days, a sensor that dropped out once, a reading that went briefly out of range.
It does not tell you that the cause is gone. A contact that failed on Friday can fail again on the water next month, at a worse moment. Whether the entry is still sitting in the memory is something you read out, not something you assume from a dark light.
Read before you do anything else
Connect the app and look at the fault list before you touch a plug or a switch. Write down the code and the text the app gives with it, plus the possible cause and the suggested checks. If you clear the memory first, you throw away the one piece of information that points at a circuit.
One caution about numbers. Control units from the FX140 to the GP1300R use one code set, and the VX1100 from 2005 and everything after it uses a newer one. Forum lists mix them freely, so the same fault can appear under two different numbers. The description in the app is the thing to trust.
What you find in the memory decides the next step
A code is stored. You have a lead. Look at the live value for that sensor or switch. If the value is plausible and steady, the fault was probably a short interruption, and the plug on that circuit is the first place to look. Cleaning the connector is something owners report helping often.
A code that comes back right after clearing, with the engine just idling, is a different story. That is a standing fault, and it deserves a proper look at the part and the wiring.
The memory is empty. Then the app has nothing to point at, and the reasonable step is to record a test ride with the data logger and look at the curves for dropouts. Voltage, throttle values and temperatures are the ones to watch. An empty memory after a light that has already gone out is common, and it does not mean someone made a mistake.
The light stays off and the memory is empty. Treat it as a one-off, but keep it in mind. If the ski starts to stall, run rough or beep later, you have a rough date for when something first happened.
What a scan cannot do here
Corrosion in a plug that has not yet set a fault leaves nothing to read. The same is true for a worn mechanical part that happens to trip a sensor. The scan narrows the field, and your hands do the rest. The Yamaha edition of the M-JET Diagnostic reads and clears the fault memory on 37 four-stroke models, and the guide to clearing the fault memory explains why timing matters when you do.
If the light is on and the memory shows nothing at all on an EX, the page on an EX with a lit warning but no code covers that case in particular. Whatever the model, read first, write it down, and only then decide whether to clear anything.
