2007 GMC 3500HD - No Start No Comm FIXED

[NPASC_mike]

2007 GMC 3500HD 6.0 gas Allison A/T

Keep having an intermittent communication issue on this truck with ALL of the modules, I suspect a poor connection at Splice Pack 205. Now, If I could just find the pesky bugger. Mitchell shows it in two different locations on this truck, one near the middle of the dash somewhere behind the temp control, and on another diagram in the vicinity of the headlamp switch. The wiring diagram shows many different color wires going to this splice pack, but the only splice pack I have been able to find is just above the park brake with nothing but dark green wires going to it. Is this SP205? I have had 3/4 of the dash out looking for this thing, put everything back together and it ran fine, but still had no Comm. Customer drove back in today because the cluster started acting crazy again, and lost power to the radio. fuses are fine.

Anyone have a clue where SP205 is really located in this truck?

Edit: NO problems communicating with the OBDII side

[steven kiser]

Man this one reminds me of the loose ground wire by the e/brake on the older Chevrolet trucks. I like the word "pesky", makes it sound so acceptable. Trucks at this level aren't as easy to diagnose. I've found that there are different harnesses used for different applications. What happens if you go to one of the plugs that the split (lug) feeds and back feed it? I've done that in these situations with good luck. go from the main feed wire that leads to the hidden lug to a connector beyond the splice. In some situations i've effectively created a new splice location. Another issue that's floating around in my gray matter is is this under warranty?

[NPASC_mike]

Truck is just out of 3/36 by time and mileage, even if it was, Dealer is 872 miles away and would have to ship it there via barge. $3000.00... Customer paid me for what I did last week without balking, Even though I only charged him a portion of what I had in it, mainly because it wasnt 100% fixed, yes it ran and I couldn't make it not start anymore, but I still had no comm. so I told him to bring it back if the dash started acting up again.

Last week I started at the ICP, unplugged and cleaned terminals, no change, so I started at all the other modules, unplugging and cleaning and dielectric grease, as outlined in the fretting terminal TSB. Body control, PCM, fuse and relay boxes, kept going until I got a change. After I did this to the BCM, the cluster came to life and truck started great. but still had no comm. I suspected Ign Switch as I have seen these do screwy things, no change after replacement. According to the wiring diagram, every thing I am missing all runs through SP205, which I cannot find. Heading to call GM in a moment, if I do find it before anyone posts the location, I will be sure to post a pic of its location better than the one in Mitchell.

SP205 seems to carry All the communication circuits and and the batt power feed for the radio.

Have not backprobed any of the wires at the affected modules except for power and ground.

[ricmorin]

I checked a competitors product. The picture you get from both is what GM provides. That appears to be a direct scan of the OE info. It probably doesn't get any better than that. Sorry and happy hunting.

[NPASC_mike]

I talked with the Dealer a bit ago. And the tech and I went over a few things as he had a similar issue a few weeks ago. Turns out I was looking at the wrong diagram. 07 is a split production year and this truck has no SP205 in it. DUH on me. However, he said too, good luck. They way he attacks this issue is to put an ohm meter across pins 6 and 14 at the DLC. Under normal conditions, you should get approx 60 ohms. Have someone monitor the meter while you start moving harnesses around. KOEO i get 57-58 ohms and as soon as I try to start it, I lose all connection., till I let it sit a while. This should get me in the area of the bad connection, then its just hunt and peck from there. This particular truck some of the comm wires go down under the body, the truck he worked on ended up having an issue near the transmission. anyway, like he said, good luck. I will post once i find the bad connection. If this harness ends up being anything like the 05 up f150's down around the LH frame rail. this should be a fun repair.

Will post findings after repair.

[NPASC_mike]

I checked a competitors product. The picture you get from both is what GM provides. That appears to be a direct scan of the OE info. It probably doesn't get any better than that. Sorry and happy hunting.

The Tech told me the same thing.. " Huh, well THAT picture doesn't tell ya much"

[steven kiser]

Have fun. I'm glad your customer understands the situation and doesn't consider you a hacker. We all have beauties like this once and a while. In my case i usually burn the late night oil or come in in the wee hours and hunt and peck. I've been known to come into the shop Saturday morning, parking my truck in a lot across the street, turning the phone ringer off, put my radio head phones on, thumb tack a blanket over the bay door windows and get to work. first thing i do i take my l.e.d. flash light and follow any harness from the bulkhead back looking for a bulbous wire or the lovely green dust we all like to see (for us in snow country) from some boob piercing a wire or not resealing a plug after back probing with a 3/4 inch piece of rebar. What i really don't like is the fact that when i find the issue i usually find about three or four inches of trashed harness because of piercing i know in my heart that there are more areas lurking just waiting for my customer to finally settle down and trust the vehicle before it acts up. If this was a ford i would bet the harness was worn through about a foot beyond the main plugs on the l/f inner fender.

On some trucks i've seen wiring issues in the rear that have caused all sorts of wild issues. years ago there were very few loops in the rear of the truck but now a day all the harnesses loop and some sensors and module feeds are in the same loop. i remember years ago i had a g.m that would cut out because of a tps issue. after banging my head against the lift post hard enough that it sounded like the church bell i found that the pressure switch harness for the a/c compressor had chafed through and was shorting out.

If i had asked what else started acting up when all this started maybe, just maybe i would have heard "the a/c stopped working about the same time" but then again sometimes i feel when i ask questions like that the customer feels like they're under a spot light and wants their lawyer present.

[NPASC_mike]

LMAO isnt that the truth. This guy has been reading on the internet about his " issue". Which makes it more fun trying to explain why just installing a VTD bypass will not fix his problem. Pouring out here right now so as soon as the lift opens up we are going to drag this inside.

As far as the for those fords, I'll take the snow over this volcanic ash and dirt that gets everywhere in and under these vehicles. Volcanic ash is conductive. and when wet, highly corrosive. Ford put two large connectors right under the drivers door, on the outboard side of the frame rail, hidden behind a nice plastic panel which tends to act like a catch all instead of a protector. I can almost replace these with my eyes closed now, All the rear body and chassis stuff goes through those two plugs, ( FP, Evap, Lights ect.) I take the plugs right out and hardwire them then seal the harness. Pretty sure I'm going to find something similar on this GMC.

[NPASC_mike]

OKEYDOKEY, Digging around, and pulled apart connector X202 ( 30 pin connector next to the hood release lever under the LH kick panel) And I didn't realize I had the key on, and wham, I hear a Ding and the dash comes to life and the truck starts fine. Plug it back in.... no dash, no start.

Start chasing that harness and low and behold, Water intrusion from the rear panel somewhere, ( haven't found that yet but I will) has destroyed the SRS module under the drivers seat. Unplug THAT module and truck runs fine and Dash works and I have communication again.

( side note. Customer stated seat belts locked up a few months ago but he wasn't worried about it and I was convinced the seat belt issue had nothing to do with the no start no comm.) There I go thinking again and it bit me in the tail.

New Module and new plug ( this one has about 7 rotted out pins) and we'll be good to go.

[ricmorin]

NICE!!!!! That happens alot.......one module pulls down the lot. Great job!

[brianp87]

Nice work, persistence.

[NPASC_mike]

Water was coming in from the cab vent on the rear panel, Bunch of dirt had collected between the grommet and the body leaving a gap. I hated charging him the other day for a few hours but everything was working when he left. Fortunately, just as I asked, he brought it back the moment it acted up again. I have read about this problem on GM cars but never seen it until now, and everything I have read never caused as many problems as this one did as far as no radio, cluster, or complete Bus failure. Hope this one helps someone down the road.

[steven kiser]

Occasionally persistence pays off and you can even feel good about it. To many times i cut my throat undercharging for issues like this. As much as a should charge the 7 or 8 hours i charge only 5. Great job and sometimes i feel the victory as if i was working on it myself.