2005 Sierra intermitent no crank

[Husker1]

Okay, I'm new to this whole forum thing so here goes. My check engine light came on last week. When I plugged in my MAC ET80 OBD II reader with the key in the "RUN" position, all the gauges went dead, the radio lost all power, and the message center started flashing "SERVICE 4WD" and "DRIVERS DOOR AJAR". The reader would not "connect" to the truck's system so I'm unable to read any codes. As soon as I unplug the reader, everything returns to normal with the exception of the check engine light staying on. Additionally, about the same time, I started to experience occasional starting problems. Turn key to the "Start" position and ....NOTHING. No clicking relays, no normal sounds at all. I've checked the battery voltage and load tested it, the battery is fine. After doing some research, I removed the starter relay from the under hood fuse block. I removed the top of the relay then reinstalled it into the fuse block so I can attempt to "manually" over ride the relay (Sometimes it even works). Now the "Security Light" on the dash is lit, this will stay on until I manage to get the engine started. Anyone have any idea what I'm chasing? I'm leaning towards a possible Pass-lock issue but I don't know much about that system and I don't see a lot about it and it's related components on the internet. Possibly a compounded issue with the emissions system (hence the check engine light)? I'm really baffled by the loss of dash power when the code reader is plugged in. (and yes, I have used this code reader on this truck before as well as tested it on my buddy's 06 GMC, it worked fine).

[txab]

Checked battery cables and body grounds? Is there power at the OBD II port?

[Husker1]

Cables and Grounds are good, clean and tight. I have power at the OBD II port, it powers up the reader but won't connect. It still cuts power to the dash and radio when the reader is plugged in. Been two days now since I've had the no start problem and the check engine light is still on.

[esox07]

Seems like the no start issue and the OBD2 port issue is likely connected somehow, but just by chance, the next time it won't crank, try crawling under the truck and giving the starter a good whack with something hard. A lot of times the starter solonoid goes bad and won't activate at random times. The whack will typically get it unstuck.

[8.1HD/ALLISON]

Possibly have a ground problem on the data line circuit? That will cause some stupid stuff to happen. I would get a wiring diagram and start by checking all the data wiring between computers. Check for shorts to ground mainly and high resistance.

 

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