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2008 Chevy 3500 LT 6.6 Duramax LMM
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Discussion Starter · #1 ·
Hi all,
I've been in the process of tracking down a few electrical issues before winter sets in (life in North Dakota lol) and I've come up against something that, in spite of my hours of scouring the various forums, haven't been able to find the answer to. I will state the problems and the course of action that I have taken to see if I could track things down, but I am pretty new to the modern electrical game only having ever had to work on a Geo Metro and an '82 K10.

In the beginning, I set out to track down
-why my door locks didn't work (except for the drivers door) when operated from either the driver's or passenger's side switches
-why neither rear window switches worked (although I could open and close the passengers side flawlessly from the drivers switch)
-why I was getting a P064c code even though my glow plugs were cycling on and off like they should to the best of my knowledge (and it wasn't kicking on a CEL)
-and why I couldn't put my truck into "relearn" for the fobs (it would flash once and do nothing)

I ended up finding breaks in the wiring at the rear passengers side door jamb which were fixed, but I still didn't have 12v at the various wires on that connector so I pulled out the interior and chased the wires back to the front driver's side canal where I found a lovely rats nest that the PO apparently called a repair (see pic). I fixed (heat shrink butt connectors) the wires that went to the rear pass. door and verified voltage there, but didn't pull every single one apart not wanting to accidentally reset something that would leave me in the lurch when I needed to leave for work Monday morning. Now the window will operate from the drivers switch but not the local switch; and I still didn't have the speaker or door lock actuator working. On the rear drivers side, I checked for broken wires to no avail, and verified 12v at each connector but nothing on the door worked still 19except for the window when operated from the driver's switch). Same with the front pass door (except that the local window switch does work). If I have good voltage at each door lock actuator connection would it stand to reason that all three are bad? How likely/unlikely is that?

The GPCM, I haven't gotten too into. I verified that I had 12v on the connector coming off the battery but haven't checked the other connection thoroughly yet. If it is the module will that have to be flashed to the truck?

After taking my pickup to my company's mechanic and having him squeeze in a very brief diagnostic test to verify that the BCM was properly functioning, I then asked him for advise on the RCDLR/keyless entry system since I also have a TPMS light on and I'm due for tires. His diagnostic tool was saying that the pickup was not equipped with a keyless entry module, but I know that it is (RPO code AP8.) He, upon noting my aftermarket radio and seeing that my truck was not communicating with it right on his tool, questioned if I had installed it (which I had not) and told me to look there to see if the correct harness was used at install to ensure proper data transfer (having seen the PO's sh*t repair job at the door sill) at which point I could determine what some, if not all of the issues, that I was having were.
I went home and on a whim looked into the RCDLR to make sure there wasn't and noticeable corrosion or anything and much to my surprise found that it had been unplugged entirely. I of course plugged it back in and it then flashed to service the 4wd, service the airbag system, and turned on the security light and wouldn't let my truck start. So, I unplugged it and everything went back to how it was before.
Then I went to the radio and pulled it out. He did use some kind of aftermarket harness (see attached pic) but used crimp connectors and did a piss poor job at it and so after fiddling with some of them I was able to get sound out of my rear pass. speaker. The harness has a green wire with a purple stripe that isn't connected to anything and a couple other wires that were just loose as well. Does the radio have anything to do with anything? Does the RCDLR need replaced/reflashed? Could my EFIlive have anything to do with it?

Thanks in advance for everyone's help with this. I know that was a little long winded, but being on the road 4 out of 7 days of the week doesn't leave much time to fix things, and I'm getting pretty fed up with this stuff...so any and all help is appreciated.

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