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That's what she said....
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Discussion Starter · #1 ·
Went to jump start my truck and couldn't get enough juice built up. After the 3rd try of trying to crank it over, no further starter engagement. Lost indication of gear selector and fuel light is one. Suspected the batteries were bad so got them replaced under warranty. Installed fresh batteries and the same thing, no crank. Cannot communicate via the OBD2 port on my Bosch unit, CTS, or my duramax tuner. Started checking fuses and found the PCM B fuse was bad. Relaced and it immediately popped again. Pulled the fuel pump relay and starter relay, no change. Went through all fuses and no change. Had to stop due to rain, can't get the truck in my shop.
Been trying to find wiring diagrams, but still at a loss. Only thing that changed since it was running was a jump start, and new batteries. Jumped off the truck as I always have.
Could I have possibly fried the starter or ECM from my two bad previous batteries?
 

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That's what she said....
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727 Posts
Discussion Starter · #3 ·

That should link to schematics. Let me know if it doesn't.

Credit @heymccall
Roswell, thank you sir, however the link is down. I tried these yesterday as well. Do you have an updated link? Thanks again!!

I also forgot to mention, this is happening with the key in the off position.
I pulled most of the relays tied to this circuit and it still pops the 20a fuse. Hopefully the rain will let up so I can troubleshoot more.
 

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That's what she said....
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727 Posts
Discussion Starter · #5 ·
Thank you!
Only had a little while to troubleshoot. Removed the following and tested with circuit breaker:
Glow plug control module
Alternator
ECM, isolating each connector at the ECM itself, then up on driver side.
Found 3 rubbed wires in the harness, but wasn't the issue. Fixed those and PCM B is still tripping breaker.
Jumped the starter at the solenoid thinking the solenoid might be the issue. Starter turned over fine, however no change.
Still no comms with ECM. Have power to 12v outlets (cig lighter).
Had to wrap up for family stuff.
Will print out schematic and trace wire by wire now on this circuit.
I also crawled under the truck and checked all connections. No chaffing from what I saw.
 

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That's what she said....
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727 Posts
Discussion Starter · #6 ·
Only had about 15 minutes of time to troubleshoot yesterday.
Just too much stuff going on in the day before daylight runs out and the bugs carry you away!
Ruled out a few wires.
Still need to rule out the FICM and TCM.
What I don't understand, is with the ECM fully disconnected, the PCM B fuse will still trip the circuit breaker, however when hooked up, I cannot communicate with it.
I should have a good amount of time today to tinker with it.
 
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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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So maybe you have a short upstream of the ECM faulting power to ground, and preventing the ECM from getting power. So your starter won't turn, and a few other things...

To be clear, you're using some odd breaker to test for draw instead of a VM, right? I think that's what I'm reading between the lines. Either that or there's a breaker in this truck I've never seen. Why do you want to test the TCM...isn't it on a separate fuse? Spring for a decent meter so you can read values. If you get a decent one that can read current and has replaceable slow-burn fuses, you'll be all set. Having said that, a 20A breaker would be pretty slick hunting this short...I'd trace the wire from the bottom of the fuse block, PCM B, #30, to the ECM. Wherever the short is, it's blowing the fuse and diverting power from the ECM, starter, serial data, ODBII power, etc

I suggest you locate and pull the EDU (not same as ECM) relay and test the draw across the PCM B fuse buss first. It eliminates a lot. See page D-20 in the doc linked above, and best of luck!

642512
 

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That's what she said....
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Discussion Starter · #8 ·
So maybe you have a short upstream of the ECM faulting power to ground, and preventing the ECM from getting power. So your starter won't turn, and a few other things...

To be clear, you're using some odd breaker to test for draw instead of a VM, right? I think that's what I'm reading between the lines. Either that or there's a breaker in this truck I've never seen. Why do you want to test the TCM...isn't it on a separate fuse? Spring for a decent meter so you can read values. If you get a decent one that can read current and has replaceable slow-burn fuses, you'll be all set. Having said that, a 20A breaker would be pretty slick hunting this short...I'd trace the wire from the bottom of the fuse block, PCM B, #30, to the ECM. Wherever the short is, it's blowing the fuse and diverting power from the ECM, starter, serial data, ODBII power, etc

I suggest you locate and pull the EDU (not same as ECM) relay and test the draw across the PCM B fuse buss first. It eliminates a lot. See page D-20 in the doc linked above, and best of luck!

View attachment 642512
Roswell, thank you sir!
Yes, for the breaker I'm using a homemade rig up that will pop a small circuit breaker, rather than burning up fuses. I do have a nice 179 Fluke Multi-Meter, however it's only good for 10a. I tried to read out the exact voltage but was unable to get a number. Was a busy weekend with mothers days and all. I'll mess with it when I get off work. I try this first and work my way up. I recently replaced the FICM (EDU), hard to believe it would be bad but I'll start there and work back through that harness. I re-tapped and loomed it all back, hopefully nothing rubbed through.
Looking through more schematics, I found that this PCM B fuse is a direct power feed to the ECM on orange wires to ECM Connector #1 at pins 6 and 20.
Also send power to the fuel pump relay
Also sends power to the EDU/FICM relay coil side - which is what your mentioning here and will be the first thing I pull today, then test across the buss. The other side of the relay coil is a ground switch from the PCM connector 1 pin 52 and is gray with black strips. This will be the second piece I inspect or test if the relay doesn't fix it.
Will update later, thanks again!
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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Fingers crossed. So..... You were playing with the FICM before? Highly suspect
 

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That's what she said....
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Discussion Starter · #10 ·
No luck.
Pulled all the relays, no change. Battery was out on my clamp meter that's better suited for amp reading. Will get more tomorrow so I can see exactly how much is being pulled across the PCM B slot.
Pulled the ECM C1 connector, no power at the wires I mentioned. Grounds were good though. Disconnected the FICM with no change as well.
I was able to turn over the starter from the starter relay by jumping it to the 40amp fuse. I would imagine if a solenoid was bad, the starter wouldn't turn over at all?
I was in the process of disconnecting the starter solenoid when a wasp buzzed me, and jammed a fingernail.....enough for tonight. Will go back through the drawings.
Again, this all started after trying to jump start the truck.
 

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That's what she said....
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Discussion Starter · #11 ·
This was why I mentioned checking the TCM. It's part of the EDU Relay.
I'm dropping the ECM off tomorrow just to ensure it's good as well.
642611
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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So maybe you're doing this and I'm not getting it, but to iso a fault like that, you should start by unplugging everything on the bus. Test the fuse buss with nothing plugged in, then add the relays to test more wire. Then test each module by hooking it up solo. If you have a short with everything unplugged, it's a loom problem. Those are honestly very common with older trucks. Understand TCM now, tks. Don't try to find the fault where it should exist.... It's probably elsewhere. Dirty buggers
 

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That's what she said....
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Discussion Starter · #13 ·
So maybe you're doing this and I'm not getting it, but to iso a fault like that, you should start by unplugging everything on the bus. Test the fuse buss with nothing plugged in, then add the relays to test more wire. Then test each module by hooking it up solo. If you have a short with everything unplugged, it's a loom problem. Those are honestly very common with older trucks. Understand TCM now, tks. Don't try to find the fault where it should exist.... It's probably elsewhere. Dirty buggers
That's what I've been doing. Sorry if my info has been unclear, it does seem like I'm all over the place. I started with the simple and easy stuff that didn't involve a lot of other circuits and worked my way up.
Today I'll test the line going to the TCM, and also see if the starter solenoid is bad. May also drop off my ECM if I have time. From there, it will be line to line testing.
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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I'm sure you know what you're doing. It's going to be a huge PITA to Ohm out all the wires, but I'm sure you'll manage. Is the starter engaging when you jumper it? I have a hard time imagining it being the source of the short, unless the relay welded itself closed. I'm assuming there's a relay. I don't have a schematic handy. But if there is, pulling the relay would be easier I think. shrug
 

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That's what she said....
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Discussion Starter · #15 ·
Found the issue!
Was the TCM, it must have an internal short to ground causing the fuse to pop.
Following the diagram I peeled back the loom to look for any damaged wire and found none.
Checked pin 3 in TCM C1 and found good power when fuse was plugged in. Ran continuity and resistance check to ensure wire is good.
Plugged everything back in except for the TCM. Truck fired right up.
Plugged in C1 on TCM and the fused popped. Removed relay, same issue. Tried grounding the TCM case but didn't change anything. Did resistance checks on the EDU Relay and associated wires, along with the power wires coming directly from the fuse buss to ECM C1 pins 20 and 57. No issues found again, just wanted to double check my work.
Nice to have it running again. Just have to figure put how to get this TCM programmed since the truck can't move!
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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I doubt you can just reprogram it. Short to ground on transistors usually indicates hardware failure. Maybe you can find one at a junkyard and have it reprogrammed to your VIN.

Now that you've arrived at the solution, here's this a day late and a dollar short. You can test the TCM pins 9 and 69 for continuity. No continuity=hardware failure.


ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008

Models affected:
2006-2007 Chevrolet Silverado Classic
2007-2008 Chevrolet Silverado

Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
Customer may comment that the vehicle will not crank or start/will not shift after the vehicle has been jump-started due to the battery run down or after installation of aftermarket equipment.

Technicians may find no communication with the TCM and or DTC U0101 stored in other modules.

A few TCM's have been returned from the field for analysis because of the above symptoms. The field returned TCM's were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM. The nodes affected described as wire bonds are wire tied to pins 9 and 69[battery ground pins] of the TCM.

The TCM is manufactured so that the heatsink of the TCM is isolated from all vehicle electrical systems including vehicle chassis ground. Do not ground welders, battery chargers, electrostatic painters or any other equipment to the heatsink. Disconnect the 80-way connector from the TCM when electrically welding etc. to the vehicle.
To avoid damaging the TCM in this manner, NEVER ALLOW the following:

1. Battery positive wires to touch the heatsink of the TCM [e.g.When jump-starting vehicle]
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amps.
3. Physical contact between heatsink and vehicle chassis or other ground circuit points.
4. Electrical grounding of devices such as arc welders, battery chargers, and electrostatic painters, or jumper cables to the TCM heatsink.

Recommendations/Instructions:
Take the following steps to check for damaged ground wire bonds if the symptoms for concern are No Engine Crank and/or No Communications with Tech II.
1. Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM. If continuity exists between pins 9 and 69, then refer to steps in eSI for O Engine Crank and/or No Communications

If the circuit between pins 9 and 69 have no continuity, then the TCM has been damaged/shorted from some sort of external source shorting to the heatsink of the TCM.

1. Inspect for the source that shorted the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.

NOTE: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.

Service Bulletin
There is a factory service bulletin for the following Chevrolet models:
2007-2010 Chevrolet Avalanche
2007-2010 Chevrolet Corvette
2007-2010 Chevrolet Silverado
2007-2010 Chevrolet Suburban
2007-2010 Chevrolet Tahoe
2008-2010 Chevrolet Silverado Hybrid
2008-2010 Chevrolet Tahoe Hybrid
Chevrolet Factory Service Bulletin OBDII Code U0101

There is a factory service bulletin for some models with U0101 code, the factory recommends that prior to any parts replaced there are several areas that should be inspected:
  • One area is the transmission connector pins, for damaged terminals or poor terminal fit.
  • Another area is the underhood fuse block for damaged terminals or the poor terminal fit and mispositioned fuses in the fuse block.
  • Another area to inspect would be the TCM ground.
  • As always powers and ground should always be load checked to make sure the circuits are able to work properly.
  • Another common area would be to check the harness for rubbing through on any sharp objects mainly on top of transmission where harness can contact a sharp area on the engine block.

Cost of diagnosing the U0101 CHEVROLET code

Labor: 1.0

The cost of diagnosing the U0101 CHEVROLET code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle's make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.

Possible symptoms

Engine Light ON (or Service Engine Soon Warning Light)

U0101 Chevrolet Description

Modules connected to the high-speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised, and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.
The serial data circuit is how the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the Data Link Connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for Diagnostic Trouble Codes (DTC). When the ignition switch is in RUN, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating correctly. When a device stops communicating on the serial data circuit, for example, if the device loses power or ground, the state of health message, it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices, in turn, set a DTC associated with the loss of the state of health of the non-communicating device. The DTC is unique to the device which is not communicating, and one or more devices may set the same code. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored code.
 

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That's what she said....
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727 Posts
Discussion Starter · #17 ·
I doubt you can just reprogram it. Short to ground on transistors usually indicates hardware failure. Maybe you can find one at a junkyard and have it reprogrammed to your VIN.

Now that you've arrived at the solution, here's this a day late and a dollar short. You can test the TCM pins 9 and 69 for continuity. No continuity=hardware failure.


ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008

Models affected:
2006-2007 Chevrolet Silverado Classic
2007-2008 Chevrolet Silverado

Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
Customer may comment that the vehicle will not crank or start/will not shift after the vehicle has been jump-started due to the battery run down or after installation of aftermarket equipment.

Technicians may find no communication with the TCM and or DTC U0101 stored in other modules.

A few TCM's have been returned from the field for analysis because of the above symptoms. The field returned TCM's were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM. The nodes affected described as wire bonds are wire tied to pins 9 and 69[battery ground pins] of the TCM.

The TCM is manufactured so that the heatsink of the TCM is isolated from all vehicle electrical systems including vehicle chassis ground. Do not ground welders, battery chargers, electrostatic painters or any other equipment to the heatsink. Disconnect the 80-way connector from the TCM when electrically welding etc. to the vehicle.
To avoid damaging the TCM in this manner, NEVER ALLOW the following:

1. Battery positive wires to touch the heatsink of the TCM [e.g.When jump-starting vehicle]
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amps.
3. Physical contact between heatsink and vehicle chassis or other ground circuit points.
4. Electrical grounding of devices such as arc welders, battery chargers, and electrostatic painters, or jumper cables to the TCM heatsink.

Recommendations/Instructions:
Take the following steps to check for damaged ground wire bonds if the symptoms for concern are No Engine Crank and/or No Communications with Tech II.
1. Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM. If continuity exists between pins 9 and 69, then refer to steps in eSI for O Engine Crank and/or No Communications

If the circuit between pins 9 and 69 have no continuity, then the TCM has been damaged/shorted from some sort of external source shorting to the heatsink of the TCM.

1. Inspect for the source that shorted the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.

NOTE: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.

Service Bulletin
There is a factory service bulletin for the following Chevrolet models:
2007-2010 Chevrolet Avalanche
2007-2010 Chevrolet Corvette
2007-2010 Chevrolet Silverado
2007-2010 Chevrolet Suburban
2007-2010 Chevrolet Tahoe
2008-2010 Chevrolet Silverado Hybrid
2008-2010 Chevrolet Tahoe Hybrid
Chevrolet Factory Service Bulletin OBDII Code U0101

There is a factory service bulletin for some models with U0101 code, the factory recommends that prior to any parts replaced there are several areas that should be inspected:
  • One area is the transmission connector pins, for damaged terminals or poor terminal fit.
  • Another area is the underhood fuse block for damaged terminals or the poor terminal fit and mispositioned fuses in the fuse block.
  • Another area to inspect would be the TCM ground.
  • As always powers and ground should always be load checked to make sure the circuits are able to work properly.
  • Another common area would be to check the harness for rubbing through on any sharp objects mainly on top of transmission where harness can contact a sharp area on the engine block.

Cost of diagnosing the U0101 CHEVROLET code

Labor: 1.0

The cost of diagnosing the U0101 CHEVROLET code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle's make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.

Possible symptoms

Engine Light ON (or Service Engine Soon Warning Light)

U0101 Chevrolet Description

Modules connected to the high-speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised, and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.
The serial data circuit is how the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the Data Link Connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for Diagnostic Trouble Codes (DTC). When the ignition switch is in RUN, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating correctly. When a device stops communicating on the serial data circuit, for example, if the device loses power or ground, the state of health message, it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices, in turn, set a DTC associated with the loss of the state of health of the non-communicating device. The DTC is unique to the device which is not communicating, and one or more devices may set the same code. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored code.
Roswell, I really thank you for all your help and input. Especially for the links to all the drawings. I do a fair amount of electrical troubleshooting at work sometimes and it's way easier having the correct diagrams rather than throwing parts at it.
I did see the TSB for the TCM, however I don't think it pertains to 04.5 to 05 LLY's - maybe just for the 6 speed alli? My connectors do no have a pin 69, and 9 is not used except for C1 which is a throttle kick down. Thanks for sharing the info!
Have a local diesel shop who mentioned they can get Delco TCM's same day, just the process of getting it to him since he has to flash it via the OBDII port. Got some friends that have the hardware/software to do it so I might get lucky and request a house call. I'll update this once I get the new TCM.
 

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Premium Member
2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
Joined
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909 Posts
My bad, I keep forgetting it's an LBZ junior. LoL. I try to help out wherever I can. I'm trying to remember..I think my LB7 had a little plastic bit over the heat sink on the TCM, and I'm not sure the LBZ does. I'll have to check when I have a chance




Very glad you have friends who can help. I'll bet a dollar the TCM is toast though, no matter what the pinout. $0.02
 
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