Cts is the coolant temperature sensor but any sensor that runs on the 5 V reference from the ECU.
The p0642 is the sensor reference Voltage,
So metering it at an unplugged sensor that runs this voltage will give whatever actual votage is there.
Obviously it "Should" be 5 V.
And when connected to say the CTS 5V in 4.5 out would be a cold engine,
!.5 would be a reading for a hot engine.
If the 5V cuircit is low then the reading coming out will be lower and will give running faults.
Same with any other 5V sensor.
Check the unplugged Voltage at any sensor that runs from the 5 v reference circuit
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