IT is the width of the pulses from the ECM that tells the FCM how fast to turn the fan. The "voltage" on the wire is either at 0 or 5 volts. The time spent in either state is what conveys the informatoin. A voltmeter will read oddly, a 'scope will show you what is going on.


For example, the fan would run slower with the 20% trace, faster with the 80% trace.
With the 100% trace the fan would run at full speed, but not due to the constant high, since their are no pulses at 100%, the fan would be in emergency mode.

80% is the closest to normal "full speed" of all traces shown below.