Mercruiser 6.2L 300 HP ECT engine: Sensor Supply Voltage C Issue

[DavidRadulescu]

I need help with an electrical problem related to one of the three PCM connectors on a 2017 Mercruiser 6.2L 300 HP ECT Stern Drive engine. Sensor Supply Voltage C “valid but lower than expected” (error code/fault 603). The sensors on this “C” Connector are used for the paddle wheel for speed, fuel level., etc. My speedometer stopped working last season so I’m not sure it’s because the voltage supply is too low (reading 1.2v instead of 5 v) or is shorted causing the low voltage problem. Any help or guidance appreciated.

[EuropeanAM]

Follow that harness, and disconnect all of the sensors and connections (note that this would likely include the fuel level sensor). Make sure voltage returns to 5V on that circuit.

If NOT, disconnect that HARNESS from the engine and recheck. Hopefully you're back at 5V on that power circuit.

Re-introduce the harness, then each circuit or sensor, until you can determine which shorted item is the problem.

DON'T assume the first one is the only one. I've found THREE (3) shorted sensors in the same circuit before.

[DavidRadulescu]

Follow that harness, and disconnect all of the sensors and connections (note that this would likely include the fuel level sensor). Make sure voltage returns to 5V on that circuit.

If NOT, disconnect that HARNESS from the engine and recheck. Hopefully you're back at 5V on that power circuit.

Re-introduce the harness, then each circuit or sensor, until you can determine which shorted item is the problem.

DON'T assume the first one is the only one. I've found THREE (3) shorted sensors in the same circuit before.

Thanks. Very helpful. I have exactly the same problem (Sensor Supply Voltage C too low 1.0-1.2 volts) on BOTH engines. If the only sensor shared between both engines is the paddle wheel sensor shouldn’t I just go directly to that sensor, find the voltage feed and cut it open to see if the voltage returns to 5 volts on both engines? I ask because there is tons of electrical tape wrapping numerous feeds and cables all nicely together between the PCM Connector C and the suspect 8-pin connector. And then I have to do this on both engines?? If I could find the paddle wheel sensor, I would just slice open the power line to it and see if that is the source of the problem. My new problem is that I cannot even find the paddle wheel sensor.

[EuropeanAM]

Paddle Wheel sensor cannot be connected to both engines simultaneously. It's either, or.

What is your BATTERY voltage showing at? On Smartcraft or Diagnostic System, preferably.

Treat each engine as a separate case. The only interaction between them should be across Can-P (unless someone has installed a non-traditional Smartcraft System).