Check your ground wire to the pcm located on the
valve cover post, rear of engine, passenger side.
It will break off or be corroded real bad.
Disconnect it from that point, i just ripped mine off,
and crimp an extension wire to it,,and reground it to
the firewall where the engine ground strap is.
This fixed my electrical problems on my 2003
yukon.
Theres also 2 ground wires located under driver
side door, under side chassis, behind running
boards, check those for corrosion too.
Also, one more ground wire, front bumper drivers
side, behind bumper on chassis there are 2 ground
wires located there, i removed them,,and reground
them to groundpoint inside engine bay with other
ground wire from pcm.
This WILL fix your problems, and while you are at it,
upgrade your factory ground wires for altenator and
battery becsuse they are crap.
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