2003 Tahoe w/ 4.8 V8

[Big T]

Looking at a 2003 Tahoe with 4.8 V8 and 123K miles for $2K. Seller’s listing says it has electrical issues. When I inquired, he said there is a constant drain on the battery. He believes it’s the stereo, but does not have the time to figure out.

How would you go about troubleshooting this issue?

BTW this truck would be for a work friend in SoCal.

 

[dbrannon79]

First question I would have is does it have the factory stereo or an aftermarket. also if it has an alarm system. that would be the clue. other than that I would do the basic test with the test light in between the battery post and the cable while pulling fuses one by one to narrow down which circuit the drain is on. if that doesn't hit something, then it's disconnect the alternator, and any other accessories that have a constant feed from the battery.

Might be as simple as a stuck brake light switch or dome/map light in the back left on!

 

[MrMarty51]

Looking at a 2003 Tahoe with 4.8 V8 and 123K miles for $2K. Seller’s listing says it has electrical issues. When I inquired, he said there is a constant drain on the battery. He believes it’s the stereo, but does not have the time to figure out.

How would you go about troubleshooting this issue?

BTW this truck would be for a work friend in SoCal.

Timing chain/sprocket set and an oil pump/pan gasket and it’ll go anothe 150,000 without having to mess with those.
At 123,000 its due for at the least the timing chain/sprocket set amd a coolant pump too while You got it offt.

 

[dbrannon79]

I can't recall if the 4.8l is the same platform as the 5.3 and 6.0 with the oil pump behind the timing cover being driven by the crank. if that is the case, do your self a favor and replace the pump, mainly the o-ring that connects the pump to the pick up tube. that one still has some time, but usually around 200 225k miles that o-ring blows out and you loose all oil pressure!

Hope the owner never used penzoil in it! the 03 burb I have sitting in my yard was given penzoil all it's life. I recently had to drop the pan for a no oil pressure issue thinking it was that o-ring. come to find out there was about 2" of sludge in the pan and the upper end is all plugged up too! it's been put on the back burner until my friend decides if he wants to pull the engine and wash it out or replace the engine. still runs fine after cleaning out the pan, but the intake and all of the upper end needs to come apart and be scrubbed out from the inside!

it was kinda funny the day I put the pan back on reusing the old pan gasket, filled with oil. proceeded to give it the sign of the Cross with a kiss, then turned the key !! I told him that day "there's no sense in putting any $$ in that engine unless we know it's still good" slapped it back together to see if any of the pistons or rods would decide to make a grand exit stage left or right!

 

[Will L.]

Depends if it is a short circuit or a battery draining component with or without key on.

Basically measure amperage pulling from battery. Leave the meter in place and pull one fuse at a time. When amps drop- that That will id the circuit.

Finding a short circuit- that isn’t fun. You work on cars so it is easily worth the investment of a good tool. Powerprobe3 MasterKit. It comes with a short finder.
YouTube videos are far more effective describing use than me explaining


The 4.8 LS has same hiccups as all LS. Oilpump pickup tube should have the 2nd bolt & bracket, yada yada, but many crush 250,000 miles.
Slow coolant loss is headgaskets (or occasionally porosity in block or heads). But rarely shown.
If they use the tahoe as a car, never haul, drive easy-it does ok on mpg. Try to keep up with traffic all the time and mpg falls off a cliff.

$2k is a gamble. I’m in love with the 6.0 LS, and will put up with a 5.3 having less power and same or worse mpg. 7.4 is a beast that drinks like Norm on Cheers. But reliable.
You have to love the rig to justify the risk of needing a new crate engine & rebuilding trans. Small engines means baby transmission instead of the near bulletproof 4l80e

 

[MrMarty51]

I can't recall if the 4.8l is the same platform as the 5.3 and 6.0 with the oil pump behind the timing cover being driven by the crank. if that is the case, do your self a favor and replace the pump, mainly the o-ring that connects the pump to the pick up tube. that one still has some time, but usually around 200 225k miles that o-ring blows out and you loose all oil pressure!

Hope the owner never used penzoil in it! the 03 burb I have sitting in my yard was given penzoil all it's life. I recently had to drop the pan for a no oil pressure issue thinking it was that o-ring. come to find out there was about 2" of sludge in the pan and the upper end is all plugged up too! it's been put on the back burner until my friend decides if he wants to pull the engine and wash it out or replace the engine. still runs fine after cleaning out the pan, but the intake and all of the upper end needs to come apart and be scrubbed out from the inside!

it was kinda funny the day I put the pan back on reusing the old pan gasket, filled with oil. proceeded to give it the sign of the Cross with a kiss, then turned the key !! I told him that day "there's no sense in putting any $$ in that engine unless we know it's still good" slapped it back together to see if any of the pistons or rods would decide to make a grand exit stage left or right!

P oil. Kind of like yuhr uh nation.

 

[DieselSlug]

The 4.8 is a good engine just as the 5.3 and 6.0 of that era, would be a reliable rig if maintenance has been done. Check warm oil pressure, common the pickup tube O-ring gets brittle and cracks resulting in lower oil pressures. Some of the earlier GMT800s have what they call piston slap on cold start which is somewhat normal and will still last a long time. Make sure trans fluid isn't burnt, and hopefully nice and red. Rest is normal car stuff, rust, play in chassis joints, etc. Price seems dirt cheap to me depending on condition. Makes me worry the electrical is more than just a drain?

On the electrical, first get a good scanner to see if there are any BCM codes. This may help narrow your search down such as radio, HVAC, seat modules, etc. Then setup a meter in series on the negative side battery (negative cable to one meter end, other meter end to negative mattery post. If it truly is just a battery drain electrical issue a good diagnostic person can figure it out (guys on YouTube like Pine Hollow Auto Diagnostics, or South Main Auto).

With the meter hooked up, read how much the drain is to begin with. IIRC should be something very low (like .02A) with it being an older less "smart" car after settling for a few minutes. When trying to find this number you need to make sure you allow time for modules to go to sleep, all doors are shut, etc. So you get a reliable static reading. Once your in this state and see you have a larger amp draw then normal you go about pulling fuses to see when the draw lessens. This would give you an idea of what electrical system branch is experiencing the draw. Just remember, some fuses you may pull and they awaken modules, which draw more again until they settle.

Not sure if I put this process in my 05 Yukon thread, but I went through it a few years back to find a drain. Mine would go dead if you didn't drive it regularly.

 

[MrMarty51]

The 4.8 is a good engine just as the 5.3 and 6.0 of that era, would be a reliable rig if maintenance has been done. Check warm oil pressure, common the pickup tube O-ring gets brittle and cracks resulting in lower oil pressures. Some of the earlier GMT800s have what they call piston slap on cold start which is somewhat normal and will still last a long time. Make sure trans fluid isn't burnt, and hopefully nice and red. Rest is normal car stuff, rust, play in chassis joints, etc. Price seems dirt cheap to me depending on condition. Makes me worry the electrical is more than just a drain?

On the electrical, first get a good scanner to see if there are any BCM codes. This may help narrow your search down such as radio, HVAC, seat modules, etc. Then setup a meter in series on the negative side battery (negative cable to one meter end, other meter end to negative mattery post. If it truly is just a battery drain electrical issue a good diagnostic person can figure it out (guys on YouTube like Pine Hollow Auto Diagnostics, or South Main Auto).

With the meter hooked up, read how much the drain is to begin with. IIRC should be something very low (like .02A) with it being an older less "smart" car after settling for a few minutes. When trying to find this number you need to make sure you allow time for modules to go to sleep, all doors are shut, etc. So you get a reliable static reading. Once your in this state and see you have a larger amp draw then normal you go about pulling fuses to see when the draw lessens. This would give you an idea of what electrical system branch is experiencing the draw. Just remember, some fuses you may pull and they awaken modules, which draw more again until they settle.

Not sure if I put this process in my 05 Yukon thread, but I went through it a few years back to find a drain. Mine would go dead if you didn't drive it regularly.

On the 1993 gmc I had, in the fuse panel, it showed two fuses, one was ECM 1 and the other ECM 2. IIRC the 2 was for the in tank fuel pump, being it was a 5.7, 350 gas engine.
Upon finding which fuse powers the ECM and pulling that fues it should cut the draw some and if it does cut it some then leave it out and start pulling other fuses until the draw goes to zero, or drops considerable. If it just drops the draw then leave out that fuse and continue pulling fuses until tje draw drops to 0.00 or some such.
I’m not sure on fuse labeling for the gas engine OBD 2 systems, if they label ECM 1 and ECM 2 or even what each would power.