No buss with new ecm

[yz3500f]

Hello all first time poster here. I have a 2002 2500 cummins that will crank but no start. I thought I had a bad ecm so I sent the ecm off to be rebuilt along with the pcm due to the age and mileage on the truck. I have received my computers back and hooked everything back up and to my frustration I still have the same issue. I checked the black and brown wire on the ecm I believe pin #30 and came back with 9.99 to 9.97 ohms according to my reading anything less than 10 ohms means it’s a bad ecm. Are these numbers so close that one shouldn’t condemn the ecm as bad again or no that’s a issue right there? Any help or advice would be greatly appreciated I will also be contacting the rebuilder tomorrow to pick their brain. 

[Tractorman]

There are many things that can cause an engine crank, but no start condition.  What made you focus on the ECM?

 

What are the symptoms?  Did the problem come on suddenly? Any codes set?

 

Any information you can provide about how the truck was running prior to the problem as well as some history on the truck would be helpful.

 

- John

[yz3500f]

Thanks for the reply I’ll start from the beginning.  The truck has been down for about a yr. It had been running ok before this issue started. I had drove it to town that morning and had it not start due to loose battery terminals. I tightened them up and drove the truck home no problems. Went in had lunch came back out and tried to start the truck. If I remember correctly it tried to start and then died and left me with a crank but no start issue. The no buss came up right away and my code reader would not link. So from the reading that I had done most ppl said the no buss was indicative of a bad ecm so I assumed with the vintage of the truck and the mileage that the ecm gave up the ghost. Fast forward about a yr and I had time to pull the ecm and pcm and sent them off to be rebuilt. Now that they are back and reinstalled. I still have the no buss no wait to start light and my code reader will not link. I tried the key trick to pull codes and the only thing that happens is my mileage blinks but no codes appear. I did the other one where you hold down the mileage pin and turn the key on and got the codes 920, 921 and 999 to flash. From what I had read these are all in the pcm and I had these same codes before. Hopefully this helps.

[yz3500f]

Update on more trouble shooting that I have done. Called the ppl who repaired the ecm and pcm no response from them. Started probing around the wiring harness that plugs into the ecm. I have 12v at pin 50 and 48 with the key on. I checked pin 3 and 10 for 5v and don’t have any. I then moved to the ground under the battery on the drivers side and cleaned that up and checked for continuity from pin 30 and I do not have continuity. To make matters more complicated tho I moved the grounds around for the vp44 to the engine and I’m not sure if that was part of that ground so I checked it to that ground location and still did not have ground. I’m assuming the next step is to undo the looming and try and track where that ground goes.

[yz3500f]

Ran a jumper wire from the ground by the drivers side battery to PIN number 30 for a ground and this did not change anything.

[Tractorman]

There is a ground wiring modification in the Articles section on this site that is called the W-T ground wiring mod.  This mod primarily reroutes the alternator output wire to the passenger side battery and addresses some poor electrical grounds that could affect the PCM and the ECM.  In particular, there is a factory ground splice that isn't even crimped near the front left side of the engine.  One of the wires in the splice is a ground for the ECM. 

 

I am not saying that this will fix your problem, but it is an important step for protecting computers and electronic devices, such as the PCM and the ECM.

 

Double check wiring connectors for the PCM and ECM and any associated connectors for pins that may have been pushed back inside the connector and are not making contact.

 

Hopefully, you will hear back from your ECM repair guy.

 

- John

[yz3500f]

I did that ground wiring mod while I was waiting for my ecm and pcm to come back. I checked my obd 2 port for power I believe pins pins 3 and 11 and I didn’t have power there so idk any more. Things iv done so far is 

1. Check for power on pins 50 and 48 and had 12v there on the ecm

2. Checked for voltage coming out of pins 3 and and 10 no voltage there on the ecm. 
3. Checked continuity on the ground PIN number 30 to the ground in front of the drivers battery and the new ground located under the vp44 no continuity. 
4. Ran a jumper from pin 30 to drivers ground in front of battery had continuity but still no start. With key on voltage from pin 30 to pin 3 reads .450ish.

5. Checked ground wires on pcm for continuity had continuity but ohms would go from 14.7 and then rapidly drop to 7.5 and hold there.

6. Checked odb2 port for power on pins 3 and 11 and had no power there 

 

 

 

[Great work!]

Check fuse 9 10amp in the side of dash. The lt green/ black wire goes to ECM pin 5.  It comes on with the key.

 

 

Do you have mice in the truck?