Howdy Yall, looking for recommendations for LMM ECM expertise in the Weatherford Tx/Fort Worth area.

mopar3

Member
Aug 16, 2017
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One side of the fuse may be a positive bus bar supplying power to it may power up multiple fuses. You need to research the diagrams and trace the circuit find out where your loosing voltage.
 

ChasFTW

New member
May 26, 2022
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Thanks Cougar281. I bought the replacement ECM from this outfit: FlagshipOne https://www.fs1inc.com/ and they advertise that given the VIN, it should be programed to work out of the box. Which it did, sort of. I still had the intermittent no-crank problem but when the truck did start, it seem to run fine, until it died without any hint of stumbling. I would like to understand this better: "program the injector values to the ecm" Is there a thread or reference document (like gmupfitter) that describes the Program applicable to the LMM specific, like what is operating system, what functions exist in re-writable code and what data (in tables?)? I gather the Injector values are likely the last type of data? And how does that data come to exist in BCM, like as a backup function? I have read all I can find at gmupfitters, that might describe the software components inside the ECM.
 

ChasFTW

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May 26, 2022
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Thanks mopar3, that is an excellent idea and I will give it a try next.
I was stymied when trying to find wiring on the circuits feeding the ECM fuses, which there are several.
Ron Nelson provided the link to gmupfitters 2009 electrical document: 2009_LD_ElectricalPickupsChassisCabs_100813, which was great, but I could not find the drawings I was hoping for. After poking around that website, I finally opened the 2008 version (LMMs being 2007.5 through 2010) and that document (2008_LD_ElectricalPickupsChassisCabs) has a section "D" including the wiring diagrams, 481 pages of drawings, that is not in the 2009 version. I should have guessed to look there sooner. F-16 TOs are the same way, if a newer model has the same wiring, they don't bother to print another TO with the same tech data, they just added the new jet tail numbers to the existing documents. Lots of good data in the 2008 Section D, but I am still assimilating it. My notes so far (specifically tracing Starting circuits)
Acronyms, page D-2
DLIS = Discrete Logic Ignition Switch
BEC = Bussed Electrical Center (fancy name for Fuse Block)
LBEC = Left BEC
RHBLK = Right Hand Block (Bussing)
UBEC = Underhood BEC
VASS = Vehicle Access & Starting Security
Drawings
D-1-Elect Schematic Index
D-340 Power Distribution (has 2x ECM fuse, DLIS fuse)
D-67-ECM-StarterRelay
D-42-Charging-UBEC-STRTRrelay-ECMinput

Half the battle has been learning the new language.
 

mopar3

Member
Aug 16, 2017
62
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Its hard when you work on all different brands and they use the same stuff but call it something different. The information is key to tracking down these issues. The injector codes are to give the ecm precise info on the flow and performance of the injector. It should run with out it just fine.
 

ChasFTW

New member
May 26, 2022
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After digesting the wiring drawings, it dawned on me I was chasing a red herring. The relevant drawings from gmupfitters 2008_LD_ElectricalPickupsChassisCabs, Section D page number and drawing sheet number:
D-343 Power Distribution drawing 12 of 26
PTR = Power Train Relay is activated by the ECM to power the UBEC_PTR busbar.
Relay-PWR/TRN relay_spst 004, feeds UBEC_PTR, with multiple fused circuits for Engine Controls Glow Plug Module, Fuel systems Fuel Heater, 2x O2 Sens/Htr, and... that bus bar continues to next drawing.
D-344 Power Distribution drawing 13 of 26
DSL-ECM, 25 A minifuse, feeds 3x wires to Engine Controls ECM Page-Dsl-1, ECM_PTR 2, 3, 4
The D-344 drawing has the 25 A fuse I thought was dead, but it was because I was testing power to fuses with the ECM unplugged. When testing with either (of two I have) ECM's plugged in, PTR is energized immediately by the ECM. Neither ECM can talk to the DLC under the dash, but perhaps one or both of them are still viable ECMs. Moving on to ohm checking the GMLAN wires and connections between the ECM and DLC next.
 

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  • UBEC_BUSBAR_2_Relay-PWR_TRN-akaPTR.png
    UBEC_BUSBAR_2_Relay-PWR_TRN-akaPTR.png
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  • UBEC_PTRbussbar_2_25A-DSL_ECMfuse_2_ECM.png
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Ron Nielson

Active member
Oct 11, 2009
398
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Berryton, KS
I have been conversing with another owner on another forum that appears to have the same problem that you do. I didn't recognize the common problem between the two of you until I read your original post again. He said that his starter relay would click 2-3 times per second and the starter would turn, but barely, and more like really drained battery. After starting and a warmup, and then shut down for a couple of minutes, his truck would start at normal speed and would run just fine. When he jumped the starter relay, crank speed was very good with the new starter. So the idea was that the ECM was powering the circuit to the starter relay in a staccato manner, on-off repeatedly. So far, he has replaced his starter and now is searching for a replacement ECM on the advice of a shop. I should mention that he went to the shop to get his new EBCM programmed after he replaced wheel speed sensors. The shop advised him that they couldn't do the EBCM programming because the ECM wouldn't talk to it. Amd that's why he is getting a replacement ECM.

There was discussion on the other forum of the problem being caused by the BCM, but no specifics on what was happening there. Keyswitch feeds BCM, which messages ECM, and that powers the starter relay and fuse. So the question is why isn't the power from the ECM to the relay constant? What causes that, and I think that's where you are also.

I hope you solve the problem and explain why this error occurs for me.
 
Last edited:

Ron Nielson

Active member
Oct 11, 2009
398
33
28
Berryton, KS
I would like to understand this better: "program the injector values to the ecm" Is there a thread or reference document (like gmupfitter) that describes the Program applicable to the LMM specific, like what is operating system, what functions exist in re-writable code and what data (in tables?)? I gather the Injector values are likely the last type of data? And how does that data come to exist in BCM, like as a backup function?
I can't fully explain the answer but I have attached the document I have pertaining to the injector values. They are stored in the ECM and the Glow Plug Control Module, but not in the BCM.
 

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  • Fuel Injector Programming.pdf
    175 KB · Views: 3

Cougar281

Well-known member
Sep 11, 2006
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St Louis, MO
I didn't look at the document that Ron posted, but the injector values are something that simply can't be programmed by someone selling you an ECM. They can program it 100% properly for your VIN, but the injector values are hexadecimal numbers etched onto each injector on LBZs and newer. These are programmed at the factory when the truck is built, and if you replace an injector, the value of the new injector should be programmed into the ECM/GPCM. In your case, with replacing the ECM, the values either don't match or simply aren't programmed in the ECM at all. As these values are stored in both the ECM and GPCM, there's a procedure using a Tech2 or EFILive that reads the values from the GPCM and will program them into the ECM, thereby fixing that issue and resolving any codes related to that.
 

ChasFTW

New member
May 26, 2022
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Thanks Ron, Thanks Cougar281. I saved the Fuel Injector Programming instructions and when I eventually find the cure for ECM Failure to Communicate, I will check both ECM and GPCM modules for Injector IQA Number, per those instructions. As I have not replaced the GPCM, hopefully it still retains the factory injector values. Hopefully my original ECM will also have the numbers, assuming the Lost Comms fault is wiring and not a dead ECM Re the programing tools, I did look at the EFILive website for their current product listings. Need to do more research on the capabilities between EFILive and Tech2, when time allows. I was having trouble measuring continuity between plugs on the GMLAN with junk test leads, so looking for pins or sockets to make test leads to better fit the plugs.
 

Ron Nielson

Active member
Oct 11, 2009
398
33
28
Berryton, KS
I'm just attempting to narrow down the area that in my mind needs to be tested further i.e. is it the BCM? ECM? the ignition switch, something else? - but I think you already replaced the ECM once without solving the problem, right? BCM has lots of inputs from varying sources, related to starting, and so does the ECM.

At the beginning of the starter circuit, have you checked for constant voltage at the BCM coming from the ignition switch (5V white wire) on BCM Pin #4 and at pin #2 the pink wire when the key is turned to start?

Have you checked the voltage at the B+ side (coming from the relay) of the #60 Jcase STRTR fuse (fuse pulled) when your key is turned to START? And do you see a constant voltage or an on-off feed to the fuse? Have you tried jumping pins 30 to 87 of the starter relay to see if the circuit to the starter thru the fuse is sound? Jumper wires can get hot immediately.
 

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  • Starter.pdf
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