Yamaha Jet Boat Diagnostics (SX, AR): Fault Codes, Live Data and Service Reset by App

Check engine light on your Yamaha jet boat, one engine not pulling like it should, or the maintenance reminder popping up: on jet boats like the SX and AR you want to know what is going on before you call it a day or pull the boat onto the trailer. With M-JET DIAGNOSTIC for Yamaha you read your Yamaha jet boat from an app on your phone, no laptop needed.

What the app does on a Yamaha jet boat

The dongle plugs into the diagnostic port and the app runs on your smartphone. Which functions you get depends on the model.

• Read and clear fault codes: every code in plain English, with a possible cause and concrete check and repair steps. Once the repair is done, you clear the fault memory.
• Live data: depending on the model, RPM, speed, engine and water temperature, intake pressure and intake air temperature, battery voltage, ignition timing, injection time, throttle and APS, and O2 sensors. Switches and relays show ON or OFF, and you can record test runs.
• Component tests (model dependent): fire ignition coils and injectors one at a time, run the fuel pump, and test the bypass or stepper motor.
• Relearning after part replacement (model dependent): idle and throttle learning.
• Service and engine hours (model dependent): reset the oil change interval, reset the maintenance and flush warning, read total engine hours and hours per RPM range.
• Vehicle data: model and engine serial number, SCC code, ECM part number and ECU software version.

Twin engines: read each one separately

Many Yamaha jet boats run two engines. In that case, read each engine on its own, meaning fault memory, engine hours and live data, even if the warning only came up on one side. Often the second engine has a stored code that matches the problem or is what finally explains it.

On a twin, a side-by-side comparison is your best tool. Do both engines turn similar RPM at the same throttle position? Are engine and water temperature, intake pressure and ignition timing close together? If one engine is clearly off, you know where to look. Hours per RPM range also tell you a lot, especially when you are buying used. For how to line up the numbers from two engines, see comparing live data and hours on twin engines. It is written for outboards, but the same approach works on a jet boat.

Common Yamaha jet boat problems and what to check

Check engine light is on

Read the code first, then act. Write down the message for both engines before you clear anything. What a code number means can vary by ECU generation, so go by the plain-English text in the app, not by lists you found on a forum.

Overheat warning

A jet boat pulls its water from under the hull, so weeds, plastic bags or sand in the intake are a classic. Look at engine and water temperature in the live data and compare both engines. If only one value climbs while the other engine stays normal, check the water path first and the sensor second.

One engine down on power or stuck in limp mode

If one engine will not rev up, read the fault memory first. Then compare throttle, APS, intake pressure and temperatures with the other engine. If the problem only shows up under load, record a test run. The data logger and test run page shows how.

Hard starting and strange codes

Two engines, a stereo, lights and pumps all draw power. A weak battery causes hard starts and often sets codes that have nothing to do with the real problem. Check battery voltage in the live data while cranking and with the engine running. More in weak battery, lots of error messages.

Faults that come and go

Moisture and salt are hard on the connectors in the engine compartment. A sensor fault that only shows up now and then is often a contact problem. Watch the affected value in the live data while you carefully wiggle the connector and harness. If the value jumps, you found the spot.

Service reset and engine hours

After an oil change or service, M-JET DIAGNOSTIC resets the oil change interval and the maintenance and flush warning depending on the model, on a twin for each engine separately. While you are at it, read the engine hours and log them in your service records. Hours per RPM range show you how the boat has been run so far.

Step by step

1. Check battery voltage and have the boat on the trailer or safely tied up.
2. Plug the dongle into the diagnostic port and open the app.
3. Read the first engine: fault memory, vehicle data, engine hours.
4. Read the second engine the same way and save the results.
5. Compare live data from both engines and narrow down the cause.
6. Make the repair, clear the fault memory and take a test run.

Clearing a code is not a repair. If the cause is still there, the code comes back. Run tests, relearn procedures and resets only with a stable power supply and according to the manufacturer's instructions.

Frequently asked questions

Does M-JET DIAGNOSTIC work on Yamaha jet boats?

Yes, Yamaha jet boats such as the SX and AR are supported. Exactly which functions are available depends on the model.

Do I need to read both engines on a twin?

Yes. Read each engine on its own and compare the values. A stored code in the second engine often explains the problem on the other side.

Can I reset the maintenance reminder on my jet boat?

Yes. Depending on the model, M-JET DIAGNOSTIC resets the oil change interval and the maintenance and flush warning, and reads the engine hours.

Do I need a laptop?

No. The dongle and the app on your smartphone are all you need, at the dock or in the shop.