2007 GMC 3500 HD No crank No start

Bill1971C20

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Oct 23, 2020
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The Truck has been sitting for 6 months. It ran just before I parked it. Now I turn the key and nothing at all. Lights, Heater and wipers work no windows or radio. Any place to start will help.
 

2004LB7

Well-known member
Dec 15, 2010
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Have you checked all the fuses? Disconnect the batteries for a few minutes and reconnect and try again. Also, check the voltage of the batteries. 6 months is a long time for lead acid batteries to sit unused
 

Bill1971C20

New member
Oct 23, 2020
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Late 2007...2008 style LMM No start No Crank. Tested fuses, if anyone has the pinouts for the ECM and TCM that would help me chase power and grounds. Thanks.
 

Bill1971C20

New member
Oct 23, 2020
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I charged the batteries, headlights are strong wiper work heat works. I will try to test the ignition and park neutral switch next.
 

Ron Nielson

Member
Oct 11, 2009
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Berryton, KS
See attached: Might want to start at the start relay. See if you have power and ground on the control side and the appropriate response on the load side. Pull the starter fuse and check it carefully Make sure there is no corrosion and that it fits tightly in the fuse holder
 

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Bill1971C20

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Oct 23, 2020
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Thanks. I do not have anything on the control side but when I jump out the relay it turns the motor. I have a cheap OBDII tester but it seems to be communicating. No luck yet. Thanks for your help.
 

clrussell

pro-procrastinator
Sep 23, 2013
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Ground the Tcm body and see what happens.

Does the prndm1 come up on the dash when you turn the key on?
 

Ron Nielson

Member
Oct 11, 2009
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Berryton, KS
You should have power on pin #71 of the relay (refer to wiring diagram post #6) with the key in the start position. Start checking upstream until you find the problem.

I do not have anything on the control side but when I jump out the relay it turns the motor.
When you 'jump out the relay' where are you getting your power source from?
 

Ron Nielson

Member
Oct 11, 2009
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Berryton, KS
Check pin 87 at the relay; key to start position should bring power to the relay. If not, follow the line up to the ignition switch until you find the problem.
 

dndj

Boost!
Apr 13, 2019
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Check pin 87 at the relay; key to start position should bring power to the relay. If not, follow the line up to the ignition switch until you find the problem.
Pin 86 on the starter relay should go to +12v when key is turned to start. If it does, then yes, leave the starter relay in place and do this check to make sure the starter relay itself is connecting 30 to 87 when energized.

If Pin 86 isn't going to +12v when the key is moved to start position, my next check would be the NSBU switch (assuming you have the Allison) on the side of the trans. Shown on the far right hand side of the schematic in post #6 - it's grounded by the TCM and tells the ECM whether the trans is in Park or Neutral before allowing the truck to start.
 

Bill1971C20

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Oct 23, 2020
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No voltage on the trigger to the Started relay. Turns when I put voltage on the trigger. I'm trying to test the NSS. Batteries went dead so I'm charging them now.
 

juddski88

Freedom Diesel
Jul 1, 2008
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I've had a couple of lmm BCMs get "lost" after sitting for a while or during a bad flash. If it cannot communicate the immobilizer key between the modules, it will not start until you jump the starter relay. A reflash of the bcm may be necessary in your case.
 

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