no run 99 chevy blazer help with diagnostics?

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S.M.

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the truck will start for a few seconds then cut off, like the security system is killing it.. when you turn the key on the security light comes on for three seconds then goes off then comes back on a second later and stays on even with the key off and out of the ignition, fuel pressure good , can't communicate with any of the computers in the truck , checked all fuses , power and grounds at ecm all good, did not check powers and grounds to body control module but that shouldn't stop communication to ecm... also not sure but only had one power at the aldl.. think there must be some sort of wiring problem somewhere.. but why can't I communicate with any of the computers, abs, body, ecm, trans, airbag,? doesn't make much sense to me,,tried two different scanners, snap on red brick and otc genysis still no comm. and the truck like I said seems as if the security system is keeping it from running,, any ideas??
 
You have lost your bus communication link.
Be careful about probing the OBD II diag connector with a test light, use a high impedence multimeter. 12V at one pin is OK.
I do not have a wiring diagram in front of me but I have seen the instrument cluster cause this problem. Start checking there.
Other than that you will have to get a wiring wiagram and check for open on all the comminication circuits.
 
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