I'm attempting to install an aftermarket head unit. The unit is not communicating with Canbus. I’ve measured the voltage from the vehicles Canbus connections and can Hi read 1 volt can Lo read 4 volts? This seems completely wrong has anyone had the same issue? 

Not sure the voltages but these are data bus connections and will have a pulsed signal transmitting data so you will not be able to measure with a meter.

The head unit has to decode the data packets to see what they are asking to be done so the unit has to speak at the same baud rate and understand what is being sent.

 

John

From what I have been able to gather the Can bus voltages are measurable with a meter and would normally be Can Hi just above 2.5 volts Can Lo just below 2.5 volts?

 

 

Based on that and plenty of other images via google, CAN-high is normally 2.5-3.5v and CAN-low is 1.5-2.5v

 

A normal meter will struggle to give you a true voltage but it does appear you may have them reversed...

The harness is as it came from the factory and I took the voltages from the correct terminals according to the pin outs?