Pcm voltage issues

[Sugmadique]

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? 

[Mopar1973Man]

8 hours ago, Sugmadique said:

How does the pcm know to provide voltage to that pin?

 

Turns on the blue wire and green both with tach signal. I'm going to bet your alternator shorted out the blue lead like mine did and fried the PCM. The PCM is protected by a 20 amp fuse and the circuit board can't handle the full 20 amp short. The PCM circuit board burns up. Mine was so bad the fiberglass burn away (physical hole in the board) there was nothing to fix.

 

Still going to need to have the PCM tested and repaired. (Thumb nail is a picture of another members damage!)

 

I did create a fix for protecting that so it never happens again.

 

Edited January 3, 2021 by Mopar1973Man

[Sugmadique]

20 hours ago, Mopar1973Man said:

 

Turns on the blue wire and green both with tach signal. I'm going to bet your alternator shorted out the blue lead like mine did and fried the PCM. The PCM is protected by a 20 amp fuse and the circuit board can't handle the full 20 amp short. The PCM circuit board burns up. Mine was so bad the fiberglass burn away (physical hole in the board) there was nothing to fix.

 

Still going to need to have the PCM tested and repaired. (Thumb nail is a picture of another members damage!)

 

I did create a fix for protecting that so it never happens again.

 

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. 

[Mopar1973Man]

Tach signal i don't think is frequency but digital info. Tach signal is typically sent by CANBus in a digital signal so as long as there is no P1698, P1694, or code for crank and cam sensors (if applicable). You PCM should have tach signal. If you have a live data tool you can confirm what the dash shows. Like Quadzilla rides on the ECM CANBus so you can't see any PCM info. Just a heads up.

[Sugmadique]

On 1/7/2021 at 10:43 PM, Mopar1973Man said:

Tach signal i don't think is frequency but digital info. Tach signal is typically sent by CANBus in a digital signal so as long as there is no P1698, P1694, or code for crank and cam sensors (if applicable). You PCM should have tach signal. If you have a live data tool you can confirm what the dash shows. Like Quadzilla rides on the ECM CANBus so you can't see any PCM info. Just a heads up.

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. 

[Mopar1973Man]

W-T ground mod handles the ECM and VP44 grounds. Thats the first thing to do.

[dripley]

I am in no way the electrical guru here but I do know that WT's ground mod is spot on. I have not had an electrical gremlin since doing the mod. 

[Sugmadique]

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. 

[Sugmadique]

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? 

Edited January 17, 2021 by Sugmadique

[Mopar1973Man]

Not really. You would have to be terminate the circuit with the same bias voltage too. 

 

17 hours ago, Sugmadique said:

don’t have voltage on the blue wire controlling the alternator and trans relay.

 

So my thought is to pull the PCM and have it bench tested by a rebuilder. Very possible the same thing happen to you as it did to me...

 

If the alternator fails and shorts out the blue wire to ground because of mechanical failure. The PCM is on a 20A fuse but the circuit board will not support the 20A fuse so it burns up the tracers inside the PCM. Hence why after having my bnech tested I found my printed circuit board was burned through completely. Required a full replacement of the PCM. To protect this from happening again I added a fuse in the blue wire off the PCM and put only a 5A fuse on that blue wire so it will not burn up the PCM again. If the circuit is burned then yes no matter the data you switch transistor is burned up. 

 

 

Here is how I stopped the problem...

 

 

[Sugmadique]

8 hours ago, Mopar1973Man said:

Not really. You would have to be terminate the circuit with the same bias voltage too. 

 

 

So my thought is to pull the PCM and have it bench tested by a rebuilder. Very possible the same thing happen to you as it did to me...

 

If the alternator fails and shorts out the blue wire to ground because of mechanical failure. The PCM is on a 20A fuse but the circuit board will not support the 20A fuse so it burns up the tracers inside the PCM. Hence why after having my bnech tested I found my printed circuit board was burned through completely. Required a full replacement of the PCM. To protect this from happening again I added a fuse in the blue wire off the PCM and put only a 5A fuse on that blue wire so it will not burn up the PCM again. If the circuit is burned then yes no matter the data you switch transistor is burned up. 

 

 

Here is how I stopped the problem...

 

 

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 

[Mopar1973Man]

Ok. Just checking...

[Sugmadique]

48 minutes ago, Mopar1973Man said:

Ok. Just checking...

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 

[Mopar1973Man]

Basically in a nutshell the PCM turns on both green and blue wires when tach signal is sensed. It might be still a defective PCM yet... if the PCM isn't getting this signal then it won't charge.

[Great work!]

My notes show a 5 volt square wave on the gry/black wire at 2x the RPM. You could try a downloading a function generator app for your phone and cut up some headphone cables and connect it to the wire. May have to cut it to prevent the ECM from loading down the signal. Set the function gen to square wave 5volts  and 30 HZ. Output that on both left and right channels red and white are the signals and the bare shield connects to ground. I have not tried it but it might work.

[dripley]

7 hours ago, Great work! said:

My notes show a 5 volt square wave on the gry/black wire at 2x the RPM. You could try a downloading a function generator app for your phone and cut up some headphone cables and connect it to the wire. May have to cut it to prevent the ECM from loading down the signal. Set the function gen to square wave 5volts  and 30 HZ. Output that on both left and right channels red and white are the signals and the bare shield connects to ground. I have not tried it but it might work.

So if I used a square wave of liquid oxygen along with a generator app with some super chilled hydrogen peroxide, could I make to the mood and back on less than 720 tanks of diesel?

 

Man I had fun typing that. All in jest because your thread was so far over my head it is ridiculous. Me I would just stick my tongue to wires and see if I saw squares or circles. 

[dave110]

[dripley]

3 minutes ago, dave110 said:

how are the libs missing this kind of stuff? Just a matter of time I guess.

[dave110]

There's a lot they're missing. After Wednesday I'll wish Ralph could send me to the moon.  

[dripley]

15 minutes ago, dave110 said:

There's a lot they're missing. After Wednesday I'll wish Ralph could send me to the moon.  

be patient my friend. not the first change of government either of us have seen. Maybe these folks can sit at the table and actually talk. tryng to keep an open mind.