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2006 sierra no start, pcm failure?

badbowtie1982

By badbowtie1982
in Ask A GM Technician

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badbowtie1982 New Member

badbowtie1982

Posted
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ill start with some background info, truck is a 2006 sierra 1500 slt crew cab auto 4x4

A few months ago transmission stated acting up and needed to be replaced. truck sat for a week during winter while i decided what to do with it. once i decided to replace with rebuilt unit truck battery was dead. boosted truck and drove it to work to pull the transmission.

truck was parked for a few more days during the swap.

once it was all back together truck would not start.

no crank no click nothing.

tested battery still good

rechecked all wiring everything looks good.

found that truck would start if key went went from off to crank quickly wit no pause at key on. required 2 cycles for truck to start

noticed shifter does not light up indicator for park or neutral but does for reverse and all forward gears, also truck no longer unlock doors when put into park.

took truck to transmission rebuilder as they had swapped out the range sensor on trans with one that was in better condition.

tried 2 other sensor with same result their scan tool show Park/Neutral with it in either park or neutral

checked all fuses underhood none blown

 

been driving truck daily for a month when it wouldnt start one morning. it stubbled on secound key cycle then would crank in short burst 1-2 sec but not start

during testing found the starter relay has power to control side and battery feed side. relay gets ground from pcm for 1-2 sec then it stops. temporarily grounded relay and truk cranked for 10-15 secounds and started. ive been driving for another month with the original issues.

i borrowed a really old scanner from the mac tools dealer and was able to confirm proper ingnition switch operation

i am a heavy truck tech so ive done what i can without a proper scan tool. 

im thinking either the pcm has bad ground circuit for the starter relay or after 2 sec of cranking the pcm sees something that makes it stop cranking. truck runs great once started.

am i right in my line of thinking?

riverbanks Senior Enthusiast

riverbanks

Posted
Posted

10 to 15 seconds to start when relay jumped,to me,sounds like a compromised power/ground issue,how's the grounds at rear of engine?

badbowtie1982 New Member

badbowtie1982

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10 to 15 seconds to start when relay jumped,to me,sounds like a compromised power/ground issue,how's the grounds at rear of engine?
The 10 to 15 secound crank with relay jumped was just one time. It was cold in the winter and truck failed to start on the 2nd short 1-2 secound crank cycle. I tried starting it another 6 or so times before jumping the relay so the cylinders probably had too much fuel from several fail cranking cycles.

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  • 4 weeks later...
badbowtie1982 New Member

badbowtie1982

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In case anyone else finds this post with similiar issues. I finally took the truck to a gm dealer. They confirmed the pcm was culprit for the no start. New or aftermarket pcm not available thru gm. I sourced a used one and installed. After performing the security relearn truck started correctly but had no communication with the throttle body module. Brought truck back to gm for programming.
Truck now starts correctly and PRND display correctly snd it will now unlock door in park.

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badbowtie1982 New Member

badbowtie1982

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thanks for coming back and posting what your fix was.
No problem i hate when the post does with no conclusion

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