07 Denali electrical issues

[chief_wiggum]

I have a 2007 Denali 6.2l 140k, a few weeks ago while sitting idling the dash lights went out, then came back on. then the gauges cycled and all the lights came on the dash (check engine, traction control, airbag, etc.) drove fine no other issues. drove it the other night, everything worked fine. went out the next morning and it wouldn't start (no click, lights barely came on) acting like battery dead. put battery charger on overnight, didn't make a difference (no power in vehicle at all) tested battery voltage it was only 4.8v (2-year-old AGM battery). removed battery and replaced with new battery, lights came on when door opened. went and got the keys, came back and the lights are off. tried starting and nothing. then lights cycled on dash and lights started coming on (overhead lights) then I was able to start it. turned it off, finished up under the hood and went to start again and no lights or power inside. Any suggestions on what to look for? thanks

 

[rdezs]

Before doing anything, I would check the battery cables and that the connections at each end are clean. The cables do tend to fail on the inside... It's not only due to mileage but rather age in years sometimes. Check resistance and voltage drop.

Then make sure you clean and check all ground locations. As this appears system wide, I'd focus on the ground connections to the engine block, as well as the ground from the back of the cylinder head up to the firewall.

While you can swap relays in the underhood fuse box to check for a bad relay, they are inexpensive and I would replace all relays due to age anyway.... Will help prevent future issues.

After that I would be checking the ignition switch.

Be sure to thoroughly check your harness for any rodent damage....

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Electrical issues like you are describing are usually related to one or more of a the failing battery condition, the failing battery cables, or a bad ground connection. You've receive great initial troubleshooting advice above from @rdezs , and I would add checking the major ground connection underneath the truck on the frame under about where the driver's feet would be.

 

[Charlie207]

Check resistance and voltage drop.

What are the measurement values?

 

[rdezs]

Less than 01 ohms resistance. On the voltage drop I like to see less than 0.2 volt... While cranking.

Keep in mind the OEM battery cables tend to corrode on the inside. That could be where you're getting intermittent connections. Considering the age, I'd be tempted to just replace them.

Don't forget to check for corrosion at the mega fuse at the battery positive connection to the battery.

 

[Fless]