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Electrical Article - PCM Ground Splice Repair

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PCM Ground Splice Repair



It's not hard and took very little time to do. 

NOTE: Do this after the other modifications have been done or you will lose the ECM, VP and grid heater grounds. 


You need:

2 10-12 gauge butt connectors 

2 1/4 heat shrink tube 2" long

Rosin core solder 

140 watt solder gun (Weller) or small butane torch

1 roll of electrical tape

Razer knife

Wire cutters

Wire striper


Remove the air cleaner housing this will open up the whole area to work in.

No need to disconnect the batteries, just unplug the gray connector at the ground wires of the right (AUX) battery. The other gray connector may have already been disconnected when the ground wires were relocated to the back of the timing cover if a W-T .

Disconnect the 3 plugs at the PCM



Cut and strip the 8 gauge wire then cut the connector off the 10 gauge wire and strip it back to fit the butt connector.



  This is the connection with the cove off.  This is splice #S109 that the grounds for the ECM, PCM, VP44, grid heater relay and data link connector.




Slide the heat shrink on to the wire were it won't be affected by the heat of soldering. Remove any plastic covering on the butt connector; insert the wires into the connector and solder.  Let cool then cove with the heat shrink.



At the PCM find the two 14 gauge black with tan stripe wires.  They go up into the split wire cover about 10" that's                                                                               where you'll find splice #S126




There are two 14 gauge black with tan strip wires coming down to the connector. One is the ground for the data link connector and the other is not used.




Repeat the cut, strip and solder process as above.




When done it should look like this.




There are no warranties implied or expressed.


Written by:

J. Daniel Martin

AKA IBMobile


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The Chrysler engineers and Cummins engineers both tried to follow sound grounding principles. They both kept the grounds short and direct. They obviously wanted to test run the engine and harness at the cummins factory and the Dodge folks wanted to be able to check their systems before the engine was installed. The problem is the PCM is grounded to the passenger side battery which seems right (good design practice)  and the ECM is grounded to the block by the starter which has a huge ground cable to the driver side battery. The TPS signal is ground referenced to the ECM and then shared to the PCM. The PCM has a different ground lay out which causes a ground difference and differential mode noise to be present in the TPS circuit. The PCM should have been grounded to the same bolt that the ECM grounds are terminated at. That would have meant an extra bolt and tool operation on an assembeld and painted truck. A signal ground return could have been put into the engine harness connector but that violates some other engineering principles. Say one of the main grounds is disconected and all the ground current for the AC blower or head lamps runs through the small signal ground and PCM it can cause a fire or at least fry the PCM. The quick fix was to put in a very large "signal ground" and then run it accros the alternator to the passenger battery so it takes a totally different path then the TPS signal wire and causes differential mode noise. If it ran the same direction and lay out as the TPS signal it would have common mode noise which is easily handled and cancelled out. The large "signal ground" should have set off red flags. The PCM should be grounded to the engine by the ECM ground with a seperate ground to the cab and another ground ran along side the fuel level sensor wire to the tank to prevent noise in that circuit too.

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