Electrical Issue, any ideas?

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absu6377

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2003 Yukon SLT 5.3 4wd: I've had the 4wd selector issue for a while. Occasionally, especially in wet weather, the truck will be in 4Lo when I start it. Even though I never shift out of 2Hi. Two weeks ago a P0449 code showed up. I replaced the EVAP Solenoid, but it did not clear the code. Next the ABS light came on last week. The ABS sensors and wheel hubs are newer and are good. Finally driving home from work today I tried to turn the volume up with the steering wheel controls, but it turned the volume down. Next I tried the volume down on the steering wheel, and it tried to make a phone call. I'd love to put the truck in the shop and let someone figure this out, but you don't own a 20 year old vehicle with 330,000 miles if you can afford to pay someone to charge you hours of T/S time. Any help would be appreciated.
I do not have access to Tech2 Scan tool. I'm able to do most work myself, but I need a little direction here.
 

rockola1971

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You need a bidirectional scanner like a Tech 2. My bet is that your serial data line is partially shorting to ground. That would cause all the weird problems of all the different and totally unrelated systems. The partially shorted data line is sending randomized low bits to the serial bus data line causing things to be turned on/off. When the Yukon "was in 4lo when you started it" was it actually in 4LO or was it just showing that on the indicator?

If the partial short condition is active when you hook up a scanner it might not be able to communicate. If this is the case then you get to go EVERYWHERE there is a data line and wiggle test to see if you can find it. Dont be surprised if you have to pull seats and carpet up. Could be under the dash too!
 
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absu6377

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Thanks for the reply and input @rockola1971.

1st: when the vehicle is in 4Lo on startup, the transmission is in 4Lo & the indicator light on the selector switch has the 4Lo light illuminated. There have been times that the selector switch has the RED Neutral light illuminated, even though the truck is in 2Hi. Usually, I put the truck in Neutral, press the 2Hi, and you can hear/feel the transmission shift.

2nd: I removed the EVAP solenoid and tested it to the battery. I heard the solenoid click, so the part is good. I reinstalled the part, cleared the code, and started the truck. I immediately saw the P0449 code back again. I am using an old Foxwell NT530 VAGcom reader as an ODBII scanner I bought for a VW I no longer have. I'm looking to add the GM software to my scan tool in the very near future.

So now my plan is to locate all ground locations so I can clean and dielectric grease all connections. After that, I'm going to remove the driver's kick panel and go over all wires out of the OBD2 connection. Trace them out and make sure wires are good and connections are tight.
 

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OR VietVet

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Known ground problems on these rigs, especially in salt roads areas. Listen to @rockola1971 on this stuff. His recommendations are typically spot on.
 

Fless

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The 4x4 issue may be the dash switch and/or the encoder motor. I've posted some info in the past about that system so shout if you need a link. A Tech 2 would help immensely with the diag.
 

Fless

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2nd: I removed the EVAP solenoid and tested it to the battery. I heard the solenoid click, so the part is good. I reinstalled the part, cleared the code, and started the truck. I immediately saw the P0449 code back again. I am using an old Foxwell NT530 VAGcom reader as an ODBII scanner I bought for a VW I no longer have. I'm looking to add the GM software to my scan tool in the very near future.

Test the evap vent valve by applying 12v to it, and try to blow through it. The vent valve at the rear of the truck is normally open, so without 12v applied you should be able to pass air through it. With 12v applied it should be closed.

Even though the solenoid clicks, the valve itself may remain open or closed, or be intermittent.
 
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absu6377

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The 4x4 issue may be the dash switch and/or the encoder motor. I've posted some info in the past about that system so shout if you need a link. A Tech 2 would help immensely with the diag.
I looked up some of your earlier posts. I found the YouTube you shared on testing the 4wd selector switch. I pulled my selector switch today and ohm'd it. It all checks out except Neutral. I'm reading 483ohms where the video said I should be up around 1,300ohms.
It has been raining here so I haven't been able to get underneath to get to the grounds behind the driver's side tire. I'm going to order a new selector switch and plan on replacing the encoder motor soon as well if the new switch doesn't do the trick.
 

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