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2004 gmc
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I'd guess a PCM problem, or a blown fuse 28 under the hood that feeds all six injectors.

Tow truck drivers are only one step up from parts counter staff when it comes to advanced troubleshooting skillz. :rolleyes: :hopeless :bonk:
 

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2004 gmc
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26,436 Posts
You could check the pink wire going to each of the injectors for 12V, which comes straight from fuse #28 as I mentioned. The PCM controls all six injectors directly, but there are other conditions under which they would be inhibited, like a passlock key cylinder security malfunction.

Do you see the security light illuminated on the dashboard?

The security system is managed by the BCM, which sends a data link message to the PCM to enable fuel delivery. Might be time for the dealer to look at the security system.
 

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2004 gmc
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26,436 Posts
The pink is supposed to be at a full 12V. With the fuse out, there's no current flow, so a high resistance somewhere in the circuit isn't going to drop any voltage and that's why it looks OK.

See if you can monitor the fuse voltage with it installed, such as with an add-a-tap gadget.

The high side of the fuse is actually connected to the RUN/START bus coming from the ignition switch, not straight to the 12V battery bus, but I bet you found that out already.

You might also have a high resistance connection from the coil side of the fuse to the injectors. There's some redundancy in the wiring to the injectors (three connector pins in the harness at the fuse block, each one feeding two injectors). All I can think of is a bad fuse socket right now. OK with no load, but can't run an injector without dropping voltage down to what you measured. A shorted coil or wiring harness would blow the fuse.
 
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