Engine speed signal from ECM

[Sugmadique]

PCM is not energizing the C3 pin 25 blue wire that controls the ac clutch, generator field or trans relay. Had a p1693 “DTC detected in companion module” and no communication with transmission. Had power and ground to pcm so I swapped with a known good PCM but no change. Cleaned all harness connectors and replaced the CKP sensor and CMP sensor. Checked pin 45 on the ecm and there wasn’t + voltage but there there was a ground signal that was all over the place before the meter finally settled at 8-9 volts. Is this supposed to be a pulsing ground or a solid signal? And should it be + voltage? Also how does the ecm ground itself? Maybe a bad ground connection on the ecm? 

[IBMobile]

2 hours ago, Sugmadique said:

Also how does the ecm ground itself?

It is grounded to the passenger battery through splice S109.  You may want to check the grounds there or modify them like this article below.

 

[Great work!]

Check grounds like IBMobile said. If you have a meter that reads frequency  probe(pierce) the gray/black wire at the pcm C1(black) pin 8. Set meter for AC volts and select Hertz. It should read about 2X the RPM frequency  1000Rpm is 16.6 Rps or 16.6 Hz times 2 is about 30 Hertz at idle. It is a square wave that goes  from 0 to 5volts peak. It originates in the ECM on pin 45. Another problem  is the dark blue wire from pcm C3 pin 25 could be shorting out to ground usually from a bad alternator with severely worn brushes or slip rings worn through. Some folks put a small inline fuse on that wire to protect the PCM. Mopar man has some articles about it.