Yamaha F20 to F100 Diagnostics: Fault Memory, Live Data and Component Tests by App

Your F60 stumbles off idle after winter storage, or the F100 on the fishing boat beeped once and has been quiet ever since. The F20 to F100 class runs smaller ECUs than the V6 engines, but they still store enough to narrow cases like these down. M-JET DIAGNOSTIC plugs into the engine's diagnostic connector, pairs with your phone over Bluetooth and shows in the app whatever your engine's ECU offers. You don't need a laptop.

Which engines are in this class

Covered are the F20G and F25G, F30B, F40F, F50F and F50H, F60C and F60F, F70A, F75B, F75C, F75D and F75F, F80B, F80C and F80D, F90B, F90C and F90D, plus the F100D, F100F and F100G. That spans everything from the twin on an inflatable to the four-cylinder on a center console. What the app can show depends on the ECU generation, meaning the year the platform was introduced, not the build year on the ID plate. A late-built engine can still run on an older platform. The app identifies the ECU and only shows what it actually supports.

18 to 30 live values, depending on the ECU

• Engine rpm, ignition timing and injection duration in milliseconds
• Intake air pressure, atmospheric pressure and intake air temperature
• Cooling water temperature, and on some engines cooling water pressure
• TPS voltage and throttle valve angle, plus ISC valve opening in percent. The ISC valve is the idle air control that meters air while the throttle is closed.
• Battery voltage, main relay, fuel pump relay
• Switch states for the kill switch, shift position switch, oil pressure switch, main switch and start button
• on some engines fuel flow, boat speed and trim level

Firing coils and injectors at the dock

Each ECU offers four to eight actuator tests. They include the electric fuel pump and the ISC valve, plus ignition coils and injectors. On a three-cylinder you fire each cylinder on its own, on a four-cylinder it's usually in pairs, cylinders 1 and 4, then 2 and 3, and on a twin both together. If one cylinder isn't pulling its weight, this is the quickest route to the cause: click the injector, fire the coil, listen for a difference. Idle learning is available on every ECU variant listed for this class. You'll want it after cleaning the throttle body or replacing the ISC valve. The app also splits engine hours into seven rpm bands from under 1,000 to 7,000 rpm, which tells you a lot when buying used.

What the fault memory knows here

Depending on the ECU, 9 to 13 fault types are stored. The app shows them in plain language with symptom and check steps, without numbers, because the same number points to a different part depending on the generation. Typical for this class: a thermo sensor out of spec, an irregular knock sensor or pulser coil signal, a TPS out of range, low battery voltage, the intake air temperature and air pressure sensors, water in the fuel filter, the shift position switch and a tripped kill switch. On top of that you'll see intake air leaks, power supply faults for the main relay, starter solenoid and high-pressure fuel pump, where the fuse is the first suspect, overcooling, where the engine never reaches temperature and the thermostat is the likely culprit, and an immobilizer communication error.

What's missing here and what stays mechanical

Electronic throttle, digital remote control and variable cam timing don't show up in the data for this class. Those arrive with newer ECU generations from the F115 up. The ECU also can't see a tired impeller, worn anodes, water in the gear oil or low compression. If the fault memory is empty and the live values look right, that's where to go next. When something's off, I'd read the fault memory and battery voltage first, then compare cooling water temperature cold and warm, and only then run the actuator tests.

Related topics

• Yamaha Outboard Idle Learning via App
• Read Yamaha Outboard Fault Codes with Your Phone
• Yamaha F115, F130 and F150 Diagnostics by App: From Cable Control to Digital Shift
• All Yamaha outboard diagnostics topics

Everything runs via app over Bluetooth, for Yamaha outboards with control unit generations from 2003. Learn more about the M-JET DIAGNOSTIC for Yamaha WaveRunner & Outboard.