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Hal, with key on I've got voltage to c1-5 but not c1-3 when…

Customer Question
Hal, with key...

Hal, with key on I've got voltage to c1-5 but not c1-3 when tested with v/m to ground c1-2 that is with the connector disconnected. Is that right? Haven't checked voltage on c1-3 with the connector connected to FICM.

Mechanic's Assistant: Is the key stripped or worn?

No have ignition voltage to all accessoies and engine runs in limp mode

Mechanic's Assistant: What is the model/year of your Chevy?

2003 lb7 engine

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

Yes Had problem with main engine harness connector a4. could wiggle wire and engine would stop. Started out with blown 25 amp fuse. temperarily bridged a4 and problem with connector okay but still engine in limp mode. thowing

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Throwing code injector main circuit open (a)

Submitted: 8 months ago.Category: Chevy
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Answered in 9 hours by:
11/11/2017
Chevy Mechanic: Chris (aka-Moose), Technician replied 8 months ago
Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Chevy
Satisfied Customers: 52,633
Experience: 16 years of experience
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Are you needing a wire diagram to follow these circuits?

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Customer reply replied 8 months ago
I have a wiring diagram from Alldata but its not very good. So if you have a better one would be great. My confusion is why I don't have voltage on c1-3 with the connector disconnected unless it's voltage generated by the FICM. My diagram shows
it as ignition voltage but I think it's really injector supply voltage.
So let me know what I should be seeing on this pin and under what conditions.
thx.
Chevy Mechanic: Chris (aka-Moose), Technician replied 8 months ago

Try this diagram. https://www.dropbox.com/s/rv5w00x9v5ivgps/LB71.pdf?dl=0

C-3 at the FICM is the power wire to the injectors with the key on.

Now that I have posted a partial or complete answer, you will see you can rate me. The deposit you have already paid is not transferred to me until you rate me. I would like to receive nothing less than 5 star excellent ratings. So if we are not there yet, please reply and let me help more. If you're not pleased, let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent replying. Thanks Chris

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Customer reply replied 8 months ago
Figured out problem--was FICM. However C1-3 Large Bosch connecter on FICM is apparently not hot with the key on
and the cable disconnected. Voltage appears to be supplied by the FICM generated from the ignition 1 (voltage C1-5) which
is used to "power" injectors when commanded and is wired to the connectors to the injectors and does not origin
from the engine harness connector. I wondered if voltage on this terminal is actually higher than 12 volts (raised by the FICM) when the cable is connected with the key on. I've read on at least some versions of the Duramax it is but don't know if true.At any rate can you email me the pdf of the diagram you sent me and include wiring diagrams from the engine harness connectors to the ficm and wiring diagrams from the ficm to the injectorsMy email is***@******.***I question whether the voltage is actually 12 volts on c1-3 under operation. Is a higher voltage generated by the ficm.
Chevy Mechanic: Chris (aka-Moose), Technician replied 8 months ago

The wire diagram i sent is the only one I have that includes the PCM/ECM and FICM. I can opt out and let another help if they can if you would like.

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Customer reply replied 8 months ago
The FICM was not in the drawing. Maybe a page is missing. The only thing I saw was the ecm. The problem with the
alldata drawings I have (although there essentially the same format as the ones you have) is there is no consolidated
drawings. In other words its in pieces. One will show the FPR and other sensors, another will show smog control, etc.
but its really all in one harness (engine harness). I was confused because on c3 on the large bosch connector to the ficm
my drawing shows ignition voltage there but with the connector disconnected there is no voltage. But after tracing wires to the injectors it became clear that was the injector supply voltage (C3 runs to the injectors). I didn't probe the wires after
hooking to the ficm with the key on (don't like to do it as the only way I have to do it is to pierce the insulation with a probe)
but at that point it had to be the ficm or a problem with one of four injector circuits putting the engine in limp mode (you know the codes this throws which I was getting). But in this case it was the FICM. If you have these drawings you can
email me in pdf form it would help me. I have 420000 miles one this truck (am ordering a new one) but the age of the
wiring continually causes problems so this won't be the last problem. My email is***@******.***
Chevy Mechanic: Chris (aka-Moose), Technician replied 8 months ago

I will opt out so another if they have the diagrams you need can respond.

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