Sugmadique

I used a snapon Verus pro, using the OBD2 generic function. It showed Engine speed at CKP sensor and CMP sensor when accessing the ECM but when connected to the PCM the was no engine speed signal. Eichlin is the house brand of Napa I think. I’m sure it’s made in China.

Does anyone know, or can anybody check what the voltage on C1 Pin8 on the PCM is at idle? I am trying to figure out if the ecm modifies the CKP sensor signal or if it just sends the same signal. I suspected I had a bad ECM and I sent it out for a rebuild from auto computer specialist and they did a full rebuild but I’m still having the same issues. I replaced the CKP sensor a few years ago due to the tach dropping out and a no start issue but I couldn’t get a cummins part so I used an eichlin sensor. When I hooked up a scan tool I had CKP signal and CMP signal but no engine speed at the PCM. For testing purposes could I jump the signal wire from the CKP sensor to the engine speed input for the PCM? At that point if I don’t have engine speed would that be a bad PCM? It’s a replacement unit from car computer exchange from less than a year ago.

Lmao, holy crap this thread went off the rails while I was gone. Anyway I had some time to work on the cummins this weekend and I brought my snapon Verus home to do some diag work. When I checked the live data I had crank signal and cam sensor signal at the ECM. The engine speed matched what the tach was reading so went into the PCM with the scan tool and there is no engine speed/ crank reference signal at the PCM. I had the alternator fail and take out my PCM before and have already replaced the PCM and added an inline fuse to protect it from that happening again. I checked the gray/black wire at C1 pin 8 and there was only 200-300 millivolts instead of the 5ish expected. I attempted to perform a voltage drop test but the voltage readings at the ECM pin 45 was the same. I checked to see if the wire had shorted to ground by doing a resistance test to ground and with both connectors disconnected I probed both connectors and tested resistance to ground and had a reading of infinite ohms. I think I have a bad ECM unless there’s something I could have missed. I already did the w-t ground mod and replaced all my battery cable ends and terminals with the military style terminals. I’m using optima batteries that are old but tested fine with my Autel battery tester.

I appreciate it, you seem to be the expert on these trucks. I inherited mine and it has a special place and I just want to have it running right

I’ve already done this, I had the alternator short the pcm as you described and I added a fuse inline when I replaced the pcm

Ok, I’ve been checking and I don’t have any readable voltage on the gray/black wire coming out of the pcm and when I check live data on my scan tool I have CKP and CMP signal and the ECM is reading engine speed but when I go into the PCM it shows Zero RPM. My tach works but it uses the ccd network to send signal from the ecm to the instrument cluster. It looks to me like I probably need an ECM rebuild at this point. Is there any way to replicate the engine speed signal to the PCM to confirm the diagnosis? Is it just a 5v reference that tells the pcm the engine is running? Can I hijack a 5v reference circuit or use a 12v to 5v converter to power that wire?

Ok finally got around to working on the dodge this weekend. We’ve had some crazy weather lately here in Texas. I completed the W-T ground mod and checked both cam and crank sensors. Hooked up the Verus Pro and checked the live data and I’ve got correct engine speed data from CKP and CMP and the ecm has engine speed data. I don’t have voltage on the blue wire controlling the alternator and trans relay. I’ve located the wire that carries the tach signal to the PCM and when I put a meter on it I’m only seeing 230 mv and it’s bouncing all over so I’m going to hook up my lab scope and see if I can get a decent wave pattern. I’m still looking for an example of a “good signal” of anyone knows what it’s supposed to look like I’d appreciate it. I’m still a noob at using a lab scope so any help would be greatly appreciated.

Just an update to the issues I’m having. I finally got my verus pro back from the dealer and I went into ODD2 generic to check for DTCs that may not have shown up with my code reader and there werent any codes but when I started the truck, there was no “engine speed” data. Previously before I had the PCM rebuilt I had a p1693 code for a fault in a companion module but it’s no longer there. What are the parameters for that code to set? My battery died before I could hook up the scope to test the cam and crank sensors. I think I’m going to try to the w-t ground mod first to make sure I’m getting good ground but if I had a bad ground to the ecm would the truck even start? What direction would you go trying to diagnose this thing? I only have a few cars with small things tomorrow and I’ll try to do some more diagnostics and update this post. Thanks in advance.

I did this while the pcm was out for repair. I have replaced the alternator and the PCM and have the fuse inline before I installed the new PCM. Is there a way to verify that I have tach signal to the PCM. I should have my Verus Pro back from repair this week. I also have an OTC encore I can try when I go back to work tomorrow but my starter failed while the truck sat and now I have to wait on the rebuild kit to even start the thing now🤬 I have a multimeter that will read frequency, if I have the correct wire for tach signal. I have already replaced the cam and crank sensors since they were cheap and I’ve had bad luck testing Hall effect style sensors before.

I don’t have voltage at C3 Pin25 on the pcm so there’s no charging or O/D. How does the pcm know to provide voltage to that pin? Does it use the engine speed signal at C1 Pin 8? If I check it and have the correct frequency and voltage but still no voltage at the blue wire can I use an ignition hot on that to make things work correctly? Will I still have the modulating ground signal on the gen field wire if there’s no 12v on the blue? If I use an ignition hot to power the trans relay will the pcm still activate the o/d solenoid?

@Dumb A did you fix this issue? I’m having the same problem with my 99 2500

Thank you so much, that article was extremely helpful. So when this first happened I removed the alternator and sent it to Napa to be tested and they sent it back saying it was fine. I’m not sure how they test it but I took it to an alternator repair shop and they said it needed rebuilt so o spent the $90 and I’ll have it back Monday. I have pcm on order and I’ll put a fuse inline in the meantime. Is there anything I can do to get moving until it arrives? I have a voltage regulator and a pigtail for it already. Will supplying the blue wire with battery voltage (and fuse)get my trans working? After I add the fuse holder to the blue wire I can leave the fuse out to protect the pcm if necessary. I just need to be able to get to work and back until the pcm arrives.

Thanks, I already have the wiring diagram and have checked continuity in the wires and they are fine. I’m just curious what is the origin point of the 12v signal on the “gen out” wire. Does the voltage come from the alternator to the pcm to let the pcm know the batteries need charged and it controls the rate of charge via the “gen field” ground signal, or if the pcm sends the 12v signal to the alternator. When I patched in a external voltage regulator the alternator was charging but that didn’t get voltage to the blue wire controlling the trans relay. I already replaced the pcm but I’m concerned that the alternator may have some issue and fried both pcm’s.

Im have a charging issue along with the transmission not having od. I checked the blue and green wires at the back of the alternator and the blue wire has no voltage. where does the voltage come from? does the pcm send 12v to the alternator or does the alternator send 12 volts to the pcm? or do both get their power from the pdc where the trans relay is?

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?