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PCM's fail, but it's pretty rare.
Symptoms, Codes, or just want to start a conversation?
Have you tried reading a file from a truck? You have a missing calibration message and ECM not found, truck would not start and the DIC was dashed out.

LLY People do this.
Your ECM may not be dead
-With the key in the run postion pop open the hood and open the fuse box
-Locate the ECM fuse IIRC it is a 20amp fuse labeled PCM 1
-Remove the fuse and then reinsert it
-You will hear the ECM switch on.
-The key must be in the run position for this to work

Google "duramax How do you know that your ECM is dead"
 

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Discussion Starter #3
Hi, I have done all the stuff that you should do if your truck won't crank,new batteries, new ignition switch, new relay, and checked all the fuses and wiring and grounds. The truck just one day would not crank, and ever since its in the same condition. A buddy of mine hooked up a snap on scan tool and says the only code is a U1000 and I believe that this means no communication between modules. We have communication with the TCM but no communication with the ECM.

What do you think?

P.S. Problem is no codes and also no prindle shifter lights and no DIC. Everything else inside of the truck works, but it seems like nothing thats controlling under the hood is working.
 

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Discussion Starter #4
Just as a note, in the fuse block under the hood, the number 1 EDU/25 Amp and the number 2 ECMRPV/15 Amp are the only fuses that are dead.
 

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Just as a note, in the fuse block under the hood, the number 1 EDU/25 Amp and the number 2 ECMRPV/15 Amp are the only fuses that are dead.
EDU fuse is for your FICM (fuel injection control module)
Google "duramax no power to 1 EDU/25 Amp fuse" lots to read
 

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What do you mean when you say won’t crank? I see this word misused so much on internet forums so much ( in my opinion). To me won’t crank means, when you turn the key the starter doesn’t do anything, some people mean it won’t start. Maybe its a regional thing?
 

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What do you mean when you say won’t crank? I see this word misused so much on internet forums so much ( in my opinion). To me won’t crank means, when you turn the key the starter doesn’t do anything, some people mean it won’t start. Maybe its a regional thing?
Crank means starter is turning the engine over; no crank means not turning the engine over. The term is often misused.

Crank no start means engine turns over but does not start.

All just as you said. It isn't a regional thing, it's lousy language.
 

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Thanks Ron, we are on the same page as to the definition of crank!
 

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How about check the actual starter, you haven't listed that above!?
 

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How about check the actual starter, you haven't listed that above!?
I'm sure that's one of the first thing he did.
Most likely he needs to repair wire rub that's causing fuses to blow. Previous post Listed are ares that need to be checked.
he needs to Google these seperately.
Google " Duranax LLY EDU/25 blown fuse" & "Duramax LLY ECMRPV/15 Amp blown fuse"
This will give him the ares for wire rub. I don't have the time to post all the links, he needs to do alittle leg work.

This is for checking starter only witch isn't the cause.
Remove the lid form the UBEC (Engine Compartment) and look for the Relay named "STARTER". Remove that relay by gently pulling straight up on it.

Your starting Circuit consists of three Interposing Devices, and associated Low Voltage control circuits for each device:
1. Starter Solenoid - Power Circuit to Spin Starter Motor.
Control Circuit is the Starter Relay
2. Starter Relay - Power Circuit for Energizing the Starter Solenoid.
Control Circuit is Transmission Switch (or Clutch Pedal Position Switch) & ECM
3. ECM
Control Circuit is Power from Fuses, and Ignition Switch Position, Powering ECM Inputs to energize the Starter Relay

The best place to start troubleshooting is the Starter Relay, because it's an easy place to locate testpoints for most of the wiring.

1. Check from Pin 30 of Relay Base to Battery Negative for +12 VDC.
If the Batteries are good, and the 40 AMP Fuse is good you should have +12VDC.
2. OHM from Pin 87 of Relay Base to the "S" Terminal of Starter Solenoid. It should be a very Low OHM reading.
3. With OHM Meter set for +20 VDC, check voltage from Pin 30 of Relay Base to Pin 87 of Relay Base. If everything is good you should have +12 VDC. If there isn't +12 VDC, then OHM from Terminal "S" of the Starter Solenoid to Battery Negative, which is across the "PULL-IN" & "HOLD-IN" Solenoid Coils.
4. The last thing to check is the Control Circuit for the Starter Relay. Pin 85 of Relay Base is Powered by a 10 AMP Fuse (IGN1) through
the IGNITION SWITCH (START) then through the Manual Clutch Switch (Man Trans - Clutch Pedal Depressed) or the NSBU Switch (Allison Trans - PARK/NEUTRAL)
and then to Pin 85. Pin 86 is Pulled "LOW" by the ECM (Ignition Switch to START) making the Relay Energize, which Energizes the Starter Solenoid, which spins the Starter Motor.
 

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G2GBY - nice informative post. It's a keeper, I added it to my PC Dmax starter folder.

We need more good Dmax tech posts like this one. Thanks
 

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Discussion Starter #13
G2GBY, thanks for that info. I just started working on the truck again. I have no communication from the ecm. I can talk to all of the other modules, just not the ecm, so I took and shipped it out to a company to check it out to see if it was good. They sent it back and said that they found a problem on the board and fixed it. I got it back and plugged it back in and it was the same. No crank ( starter not turning over the engine ).
I can turn the engine over by jumping the relay or at the starter. I think that I am going back to chasing wire chafing by the ecm wiring.
 

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Here are a couple of videos of someone doing the diagnostics. Perhaps it will inspire you.



Part 1


Part 2


Keep looking. Don't give up.
 
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Discussion Starter #16
G2GBY, I have checked just about every wire that is in the engine bay or under for wire rub. I am running out of ideas. I have been on the computer for hours checking the forum for any ideas as well as Google. I think Google may start charging me to log onto it because of the amount of time I have spent on it. In other situations I have found that I am looking too hard and it maybe something right in front of me that I am missing. I think I am going to go back and start with a no crank no start problem again and just retrace everything I have checked. Any ideas would be appreciated.
 

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Discussion Starter #17
Well I am back to war on this truck. I have had some medical problems that made it hard to work on anything. Is there anyone on the forum that can take and bench test this ecm. This way I can know for sure that it is fried.
I am pretty sure that after chasing this problem for as long as I have that there really is nothing left to test.I think that my problem started when one of my batteries was very low for a while and when I hooked up my trailer is when the truck did not start again after I shut it off it went into this condition that I have now and it has never changed. I am thinking that if it is the ecm I could have one custom for better fuel econ. or better power. This truck has never had any mods to it since day one. That is the problem, I never had any issues with it before now.
 

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My truck is running now after a new computer. Thanks for all the help!
Glad you got the issue resolved.
Thanks for giving us an update!

:thumb:
 
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