Need a diagram of all the 5v power sensors to trouble shoot a Sensor Supply Voltage Low

[Chris Lovlecae]

Does anyone have a diagram where all the 5v powered sensors live on a 350 MAG MPI EC engine? My boat popped a 602-5 Sensor Supply Voltage B "The signal received is valid but lower that the expected range." Then Vessel View says "Sensor power supply voltage is low."

Of note, my speedometer dropped to zero going about 25 MPH when one of these alarms tripped on the way back to the dock. Could a bad pitot sensor be the cause of the low voltage if it's bad? I can't find a good diagram of the sensor layouts and am not sure if the pitot sensor is even part of the Sensor Supply B. I will check the pitot port (I have a Bravo III outdrive) for a clog. There is lots of grass floating here at the moment so it could be a coincidence.

I'm amazed at how crazy the system seemed about this alarm. You would have though the world was about to end.

 

[Fun Times]

From a section of a manual like linked below suggests:
602 Sensor supply voltage B -4 Range high Sensor supply voltage is above specified level. This supply powers the MAP sensor and demand sensor 2.
B-5 Range low Sensor supply is below specified levels.

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Finding a wiring diagram for these engine models could be pretty tough to locate online..I believe you'll need the manual like seen in ebay to help here if that number is your ECM model design.

Typically the gray wire is the 5 volt power wire for the sensors and yes the transom wire harness / sensors do use the 5v system too and bring the engine down.

Range low could be a bad ground someplace or bad sensor which yours looks like it covers 2 things in which I believe the demand is part of the MAP sensor too but don't recall exactly at the moment.

If possible, order the book and share your experience as you go.

You may be able to rent a rinda for sale | eBay Rinda Diacom Marine diagnostic cable and software with Adapters... You'll need to know what model ECM you have to find the right adaptor though.