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Discussion Starter #1
I have a 04 LB7 set's a code p0381. I look in my FACTORY service manual and there is no p0381 for the LB7' but there is for the LLY. The wiring diagrams are different and the trouble tree's are different for diag. the glow plug circuit.
What happened is I installed a FASS pump and the G/P light stoped working, sent the cluster out, it's good, the G/P's worked at that time, started ck'ing the circuits, 12 volts to G/P module, can't make heads or tails out of the ECM plugs, the numbers are so small I can't read them even with a mag/glass.
I ck'd the the AIH today it's no longer working, ii was a few days ago when all this started.
I guess I should ck and see if the G/P's are still getting voltage.
The wiring diag says the dash light is cir# 36 dark blue but the numbering list in the book says it is # 52 light blue:confuzeld
I know this is a split year truck as I have trouble getting the correct boost sensor from the dealer even with the vin# and the old part in my hand.
Can anybody shed some light on this monster it's killing me:think: Thanks for all the help in advance I know it will come
 

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Is your VIN 1 or 2?
 

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Discussion Starter #3
Sorry about not putting in the VIN it is a 1 also it is stock except for a 5' exhaust and a SuperChips tuner that I run in 2nd mode for tow power
 

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Discussion Starter #4 (Edited)
I rechecked my glow plugs and intake heater today, they are both working correctly. I pulled out the inner fender panel so I could get to the ECM connector easier and was able to I.D. the numbers on the 80 pin connector (blue). #52 is light blue #36 is light green with a brown tracer.
#52 pin should have 9.5v it reads open? is that possible? on a voltage circuit. Pin #36 reads .635v So I have to guess that the ECM is faulty, everything else checks OK.
The people in town that work on these trucks say that the ECM's usually don't go bad in these trucks.
I wonder what a ECM cost from the dealer, then it has to be flashed.
Is there somewhere in the aftermarket that repairs them, that anybody would recommend.
Anyway, that is what's new with my '04 Duramax vin 1 today
Thanks for any help and or advice offered, all is welcomed :)

I noticed I said it had 5' exhaust it has 5" exhaust, but I'm sure everybody knew that!
 

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If you need a ECM I have one, SoCal can repair them for about 100 bucks or so.
 

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Discussion Starter #6
How do I get a hold of Socal? to inquire about rebuilding my ECM. Sounds like they may be close as I am in Northern Cal.
 

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Discussion Starter #8 (Edited)
Went out to theshop to do an amp draw test on the glow plugs and the 1st read 10 amps 2nd 2 amps 3rd 3 amps. I'm thinking to myself no way so I ck the other side with a test light no power, no power to AIH, I check the original side I tested it's dead, no power, power to the module so I am going to replace the glow plug module on Monday, see what happens, worst thing it burns to the ground.
I'll keep you posted, Steve
 

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I'm assuming this is a Cali emissions truck and you have an individual power wire for each glowplug? If so, then the ECM should set a code specific to each bad glowplug circuit if you had a bad glow plug. The code for the LLY might be the same for your truck. 03-04 LB7s have the same basic wiring as the LLYs. Stupid question here, but when you went back to the other side and found nothing power, it wasn't because the glowplug timer had timed out was it? I feel like that code still applies to your truck even though it isn't in your manual.
 

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Going by the wiring diagram, the IAH has it's own diagnostic circuit so if something was wrong with the IAH or it's power circuit, it should show it's own code. You could also check continuity from the terminal on the glow plug controller to each glow plug to make sure the wiring to them is intact, at least to some extent. And for the ECM, pin 52 receives voltage from the field. If 52 does not have the correct voltage it should throw a P0380. Where does pin 36 go in your diagram. It doesn't show a pin 36 in my diagram, just J2-6, and J1-29, -52, -62, -78. I wouldn't believe that your ECM is at fault, although stranger things have happened.
 

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Discussion Starter #11 (Edited)
The truck is a a 04 vin 1 cal emission's. single wire to each G/P. I have the LB7 engine not the LLY different diagram in my book. It shows the G/P signal going from the G/P controller to ECM pin52 C1 and the wait to start signal pin #36 dark blue C2 ECM going to the cluster. Do I back probe this wire or disconnect and check the ECM directly?
It looks to me like this blue wire pin #36 feeds the light in the cluster and if the G/P module is working or not the cluster light should still work.
 

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Discussion Starter #12
So I went out and checked the voltage at pin #52 5.65 then I checked pin #36 clear connector dark blue wire 0.11v, did this with it connected and unconnected.
There is supposed to be 9.5v at pin #36. Dose this mean the ECM is bad?
In the P0380 Flow Chart the value is 5.6v so I am guessing that is glow plug signal from the G/P module to pin #52 ECM C1. The flow chart dose not address the wait to start light that I can see.
 

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Thanks, with your description I was able to find the wire on a different diagram page. It would have to be back probed. The ECM sending the enable for that light might be based on multiple inputs. The wiring diagram I have shows there are 3 possible inputs to the ECM that might have an effect on enabling the light. J1-52, J1-29, and J2-62. My diagram has them listed as Glow plugs diag, IAH mon(monitor I'm assuming), and IAH diag, respectively. Has your IAH ever had voltage during any point in your testing? It has 2 inputs to the ECM that might effect the WTS light enable.

Edit: You were posting as I was posting, but even with the new info I think this post is still relevant.
 

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Discussion Starter #14 (Edited)
Yes the AIH is working and the G/P's are getting power today. I don't know if I have an intermittent G/P module or what maybe I just rush thru checking stuff and get timed out.
I assume j1-52 is the same as c1-52 in my wiring diagram. 29 & 62 are supply voltage for the AIH which is working and clicks off after about 15 seconds. I see where they no correlation to the WTS light.
I guess the next thing to due is have the ECM tested, I'm sure there is some place in Sacramento that can do that for me. I'll check on that tomorrow and give you an update after or if I get it fixed.
 

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The more testing that you do, the more I believe that P0381 is a code specific to the internal circuitry in the ECM.
 

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I just read some other forums with your problem and 2 said it was a problem with the underhood fuse box, basically loose connections, you did say you had intermittant power problems to the glow plugs, thats where the mega fuse is for the glow plugs and IAH. I think it is worth a look . just trying to help----charlie
 

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Discussion Starter #17
I can certainly check that, just have to take the lower cover off. It wouldn't be the first time I saw an intermittent fuse.
I'll post what I find later today.
But I believe it is in the ECM, see if I can't find some answers today from an expert or two who repair these things.
 

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Discussion Starter #18 (Edited)
I haven't had time to work on the truck for a few days. Rechecked everything today and decided to send the ECM out to get checked and repaired, will take a week or so before I get it back. I will update everybody when it comes back and I get it reinstalled and hopefully all is well with my truck again. :)
 

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I haven't had time to work on the truck for a few days. Rechecked everything today and decided to send the ECM out to get checked and repaired, will take a week or so before I get it back. I will update everybody when it comes back and I get it reinstalled and hopefully all is well with my truck again. :)
What was the outcome after sending your ECM in to get fixed?
 
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