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Old 09-07-2008, 10:05 PM   #1
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Unhappy 1996 GMC Sierra W/no check engine light and can't read pcm

Hi...I have a 96 gmc sierra Stepside Z71 xc, 5.7/4wd/auto...I bought it 2 months ago and have been trying to figure out why when i start the car the ses light does not light and when i try to read my computer, my scanner says it can't communicate...I have used the scanner on my 96 suburban without problem, so i know the scanner is working...the truck seems to run ok...it had a 95 single cat exhaust with homemade o2 sensor ports wich i have since changed for the correct duel cat setup...I also noticed that the seatbelt warning light, key in ignition, headlight warning buzzer don't work either?? maybe coincidence?? I have checked all fuses and the wires all look in tact...I need help or i wont be able to pass inspection...any help you can give is greatly appreciated...thanks in advance...John
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Old 09-08-2008, 12:27 AM   #2
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I have seen this many times on the older vortec trucks
Get a new pcm and what that does
That always worked
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Old 09-08-2008, 08:23 AM   #3
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Default thanks, but tried it

hi and thanks for your quick reply, i did buy a pcm from ebay from a 96 tahoe with same motor and trans etc...plugged it in and no change...is there anything special you have to do when changing pcm?? after i swapped them, i didn't even notice and change in the way the motor ran and i assumed there should have been while the truck relearned its functions...thanks
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Old 09-08-2008, 05:45 PM   #4
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Do you even have power to your diagnostic port? Check your fuses. Your check engine light is probably burned out and someone probably removed your door chime/buzzer box under the dash.
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Old 09-08-2008, 06:04 PM   #5
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Hi and thanks for your reply...I have checked all fuses and they are good, there is no power to the port, i was wondering if there was a relay or something that might have been unplugged or be bad...and i thought the ses light is an led...so it really can't burn out like a conventional bulb...I think it is more than a coincidence that the ses and port are both dead, just can't figure out why...thanks for your thoughts though...every little bit helps
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Old 09-08-2008, 06:31 PM   #6
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if there is no power to the prt that is the problem,it will not work if there is not power to the prt
I know you know this but the port runs off the cig lighter fuse
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Old 09-08-2008, 06:40 PM   #7
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I have been boggling minds from coast to coast...lol...the no ses light and port seem to be to much of a coincidence, i was hoping there was a trick to disable both and a fix to get em working again...can't really figure out why someone would do it though....thanks for your reply
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Old 09-08-2008, 08:28 PM   #8
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also all of the lights in the cluster are bulbs. check to see if they are good.
if you can't find the bad fuse for the obd2 port then run a 12v fused power wire to it.
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Old 09-08-2008, 11:06 PM   #9
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thanks, i'll give it a try tomorrow...keep your fingers crossed
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Old 09-11-2008, 09:37 AM   #10
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CEL is not an LED. Just a regular bulb.
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Old 09-11-2008, 09:37 AM
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1996, 96, diagnostic, diagnostics, gmc, location, pcm, port, power, problems, ses, sierra, tahoe, tahoo, z71


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