Help! Crazy! Showing codes; p0740, p0785, p2761. Also ABS , E- brake , 4x4 lights up. Won’t start “ most” times, but I’ve found by tapping fuse box under hood it starts. I’ve check all grounds I know of.
Multiple codes on gmc sierra
- Thread starter Jamiewildwings
- Start date
- Jul 22, 2015
- 2,724
My bet is that it's your ignition switch. They're cheap (but it's considered an electrical part, so likely no 'return' privileges.) While you have a Sierra instead of a TB/Envoy, the symptoms look similar.
If you purchase one, make sure to get a genuine GM part (AC Delco, I believe; the other option would be Delphi). No others for this one.
Search the threads here for 'ignition switch', and see if you don't agree. You'll also find helpful tips for installing it (and some on diagnosing it, I believe.) Also, check here for a good YT video by one of our now inactive (I won't say 'former') members who has some really good diagnostic skills (he's a mechanic, by trade.)
If you purchase one, make sure to get a genuine GM part (AC Delco, I believe; the other option would be Delphi). No others for this one.
Search the threads here for 'ignition switch', and see if you don't agree. You'll also find helpful tips for installing it (and some on diagnosing it, I believe.) Also, check here for a good YT video by one of our now inactive (I won't say 'former') members who has some really good diagnostic skills (he's a mechanic, by trade.)
Mooseman
Moderator
Thread moved to Full Size section.
If the ignition switch doesn't fix it (which I concur with @Reprise ), then definitely something going on electrically. Your "tapping on the fuse box" would lead me to believe that something is up with wiring or power. It's not unheard of of a fuse box going bad or melting down or wires under it breaking.
And I assume you checked ALL the fuses with a DMM, not just visually?
If you can get a hold of the wiring schematics for this truck, see which circuit is common to each of them.
If the ignition switch doesn't fix it (which I concur with @Reprise ), then definitely something going on electrically. Your "tapping on the fuse box" would lead me to believe that something is up with wiring or power. It's not unheard of of a fuse box going bad or melting down or wires under it breaking.
And I assume you checked ALL the fuses with a DMM, not just visually?
If you can get a hold of the wiring schematics for this truck, see which circuit is common to each of them.
- Jul 22, 2015
- 2,724
FYI - I have two sets in .PDF format...
One is listed for 2000-2005 (the page headers list as 2002) - 97 pgs, 17MB, non-searchable (Ctrl-F)
The other is 'engine' specific from 2006 MY, but only 571K (and it is searchable)
I'll post the smaller one here, in case the OP can get some use out of it on an 'immediate' basis.
The larger one... @Mooseman - PM me if there's a place I can upload it to - guessing that it's best not to tax this site's storage cap with something that big.
Actually, I can upload my entire copy of the SM, if there's someplace to store it. I can see if it'll compress, but it starts out at 737MB, all-in.
DocBrown
Member
- Dec 8, 2011
- 501
Also check your battery voltage. Should be 12.6 or higher. If it's closer to 12 or lower you could have a bad battery. That will make your computer go crazy because there isn't enough voltage to fully power the sensors. I bet if you try driving it, it's in limp mode.
What year, engine, and miles?
What year, engine, and miles?
Thank you!
It’s a new battery, but I’ll check it! 2004 5.3 270 thousand miles😳
Mooseman
Moderator
tblazerdude
Member
- Dec 4, 2011
- 321
--^-- +1.... and this video is one from some of our Hispanic Brothers (GM Mechanics) that... even in the complete absence of being able to speak the language... you will still be able to dope out how the VOP (Video Original Poster) performed his diagnostics on a similar class GM Truck by using a DMM first to check the fuses in the circuit and later to use a Snap-On Diagnostic Scanner to discover that the Ignition Switch was having sketchy voltage issues that caused the Transmission Control Solenoids to get "Wonky". I watched the entire hour + long video and have tried to distill the VOP's discovery down to this start location (around 50 Minutes along) of the critical stuff and have provided a single screen print image of the Suggested Repair Procedures. I hope that this is where the problem lies... and remember that last suggestion posted above here is for you to "Check The Grounds...":
From 50 minutes onward....
But... Please bear in mind that if the "problem cascade" is NOT located in the Ignition Switch... then this should lead you to getting under the vehicle to diagnose the "PINK" Wire inside the Transmission Connector Harness leading from the (Mickey Mouse) Ignition Switch Wiring Harness that services ALL of the Transmission Solenoids in the Shift Sequence... any one of which could ALSO have failed enough to make the Adjacent Solenoids inoperative. Make sure that if you "puncture probe" to examine voltages of any wires in that harness ...that you paint those areas over thoroughly with "Black Liquid Electrical Tape" to ensure that Road Salt does no enter into the wire insulation and cause it corrode the copper strands inside enough to fail over time.
The VOP shows just how thorough he was in keeping after the issues one at a time and finally "running these problems to GROUND". In this case... the Diagnosis lead to the need to run a Bad Wire By-Pass in the Ignition Switch Harness to finally solve the problem. We could use some help here from our Spanish speaking Members in translating exactly what the VOP said he did on specific wires nested inside that harness that became the focus of his solution.
From 50 minutes onward....
But... Please bear in mind that if the "problem cascade" is NOT located in the Ignition Switch... then this should lead you to getting under the vehicle to diagnose the "PINK" Wire inside the Transmission Connector Harness leading from the (Mickey Mouse) Ignition Switch Wiring Harness that services ALL of the Transmission Solenoids in the Shift Sequence... any one of which could ALSO have failed enough to make the Adjacent Solenoids inoperative. Make sure that if you "puncture probe" to examine voltages of any wires in that harness ...that you paint those areas over thoroughly with "Black Liquid Electrical Tape" to ensure that Road Salt does no enter into the wire insulation and cause it corrode the copper strands inside enough to fail over time.
The VOP shows just how thorough he was in keeping after the issues one at a time and finally "running these problems to GROUND". In this case... the Diagnosis lead to the need to run a Bad Wire By-Pass in the Ignition Switch Harness to finally solve the problem. We could use some help here from our Spanish speaking Members in translating exactly what the VOP said he did on specific wires nested inside that harness that became the focus of his solution.
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I’m going to try ignition switch in morning. I think I’ve check all grounds, but where about is the wheel well ground? Which side?
G106 *** From Battery to Engine Side of Left Front Wheel Well -or adjacent Frame Area.
G304 *** Left Frame Rail near ABS Pump
G305 *** Left Frame Rail near Fuel Pump
Don’t take this the wrong way… but since you live in Texas ... there is better than Even Odds that you either work or live at or near either a Ranch or a Farm… and if you have been parking your vehicle near places that store Grain or Corn and the Rodent population is at a high point… don’t put it past 'Mickey and Minnie' to have sought out and set up a homestead inside of your SUV (under the carpets, too) if you park it inside of a Closed Area with the windows cracked open even a little bit.
They will gravitate toward that one, lone McDonald’s French Fry that is still stuck along the edge of the passenger seat once they get a whiff of it and will pursue it at all costs. Their nocturnal activities activities will also extend to roaming around the engine compartment to get warm and other under-body areas that allows them to get above ground protection from the elements and from predators as well.
All rodent dentition requires that they gnaw incessantly on things to constantly wear down and sharpen their teeth ...and Automotive and Residential Plastic Coated Copper and Aluminum Wiring are some of their favorite targets. So if you have been finding any “gifts” left behind by the Lil’ Turd Droppers inside of the vehicle on the floor or Dash board areas… then this unfortunate possibility raises its Ugly Little Head to add to the calculus of this repair. Unfortunately... the weakest wires in the bundles (gauge wise) are usually those that service the Databus and its common convergent Splice Pack under the dash knee bolster area.
G304 *** Left Frame Rail near ABS Pump
G305 *** Left Frame Rail near Fuel Pump
Don’t take this the wrong way… but since you live in Texas ... there is better than Even Odds that you either work or live at or near either a Ranch or a Farm… and if you have been parking your vehicle near places that store Grain or Corn and the Rodent population is at a high point… don’t put it past 'Mickey and Minnie' to have sought out and set up a homestead inside of your SUV (under the carpets, too) if you park it inside of a Closed Area with the windows cracked open even a little bit.
They will gravitate toward that one, lone McDonald’s French Fry that is still stuck along the edge of the passenger seat once they get a whiff of it and will pursue it at all costs. Their nocturnal activities activities will also extend to roaming around the engine compartment to get warm and other under-body areas that allows them to get above ground protection from the elements and from predators as well.
All rodent dentition requires that they gnaw incessantly on things to constantly wear down and sharpen their teeth ...and Automotive and Residential Plastic Coated Copper and Aluminum Wiring are some of their favorite targets. So if you have been finding any “gifts” left behind by the Lil’ Turd Droppers inside of the vehicle on the floor or Dash board areas… then this unfortunate possibility raises its Ugly Little Head to add to the calculus of this repair. Unfortunately... the weakest wires in the bundles (gauge wise) are usually those that service the Databus and its common convergent Splice Pack under the dash knee bolster area.
