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I have a 2016 26 SD . The digital gauge and the analog gauge both read 0. I have flushed water from the front of the outdrive. All the way to the sensor. I have replaced the sensor. That did nothing. I even took a syringe and hooked directly up to the sensor and put pressure on the sensor. That still didn't make speedometer to move. The sensor has 3 wires going to it. Im assuming 1 wire is hot. 1 wire is ground. and 1 wire is a communicating. Does anyone if this is true or where I could find a wiring diagram. Or does anyone no of something else to check. All of my other gauges work as they should.

Where is the sensor? Near the speedometer gauge, or near the pitot tube? I think Faria made a lot of the instruments in Cobalt boats, but I'm not familiar with the configuration you're describing.

Most of the time, flushing the pitot connecting tube and use a little drill bit to make sure the pressure pickup on the outdrive isn't clogged seem to solve it, but it sounds like you've tried that already. I'm starting to suspect a bad sensor unit, but a picture of that would help.

The sensor is mounted on the back of the stern behind the engine. I have already replaced the sensor that I got from my Cobalt dealer. I can flush water through the front of the out drive all the way to the sensor freely. But speedometer just reads 0.

My next step would be to determine what sensor I have, and measure voltages coming off the sensor. Assuming they're correct, I'd pull the speedometer and make sure the wiring is correct, then make sure the same voltages are reaching the speedometer from the sensor.

If the speedometer is receiving good speed signals, you've pretty much narrowed it down to the speedometer. I'd try powering it and applying different voltages to the speed input to see if the speedometer reacts based on the input, but if you know the input is good from measuring the voltages on the wires going in, you sort of know that it won't.