Help! Electrical diagnosis needed.

[yukonese]

2001 Yukon SLT 5.3L 4x4, 130K miles, 1st owner.

Day1,

• Everything was normal, change oil light on, I changed oil in the evening, no action after poured 6 quart Mobil1. I planned to reset the computer next day as usual.

Day2,

• Unlocked the door by remote (electrical power should be OK at this moment) in the morning.
• When I tried to start the engine, nothing happened. I noticed no lights on in the cluster or interior.
• Central door lock didn't work, remote, radio, didn't work either.
• Opened the hood, the hood light didn't turn on.
• Checked battery voltage from the back of the terminals, 5V only (poor connection?). I suspected the Bosch battery was bad, it was 3 months old only. I decided to deal with it after work.
• Back from work, checked the voltage again, 12.7V, but no hood, interior lights on.
• Took the battery to Pep Boys (where I got it from), they checked the battery, 802 CCA, cannot be healthier.
• Put the battery back, hood light went on, a good sign. Engine started successfully, everything seemed back to work.
• I drove it around the residential neighborhood slowly, after around 1 mile, suddenly steering power lost, I found the engine RPM went down to 0, obviously the engine was off. The truck was still moving by momentum for about 200ft, I managed to pull it over.
• During moving with the engine down, the head/cluster lights were still on. The symptom was different from that in the morning.
  
• I restarted the engine successfully a couple minutes later, then went straight home.

Questions,

• Pep Boys pointed me to check fuses, especially the main fuse. I checked all big fuses in the electrical box, they are no bigger than 50A, all OK. Any other fuses I should check? Any single one can bring down the whole car?
  
• They found water in the battery terminal connection area. The possible reason is, I washed the car in a station with high pressure spray, but it's one week ago. I have been there for years, never found a problem.
• What is the possible electrical problem causes the engine to shot off during driving? But with the lights on. I didn't have any electrical related issues in my 19 year ownership.
• Could be the same reason that causes no any power in the morning, and shot off engine in the evening?

A bit long, I tried to mention every detail for experienced people to give me some suggestions.
Thanks in advance.

 

[Doubeleive]

I would take a close look at your battery cables and grounds.
even if they "look" ok I would advise spending $2 for a wire brush and clean the cable ends and where the ground bolts to the engine block and frame.

doing the above may or may nor resolve the problem, either way I would avoid pepboys

there is also the possibility the battery could be bad, it may have a internal short or bad cell, I have had battery's show 12v and then literally not have enough power to unlock the doors
since you stated it showed only 5v and then later was 12 again would make me suspicious of the battery.

again avoid pepboys if at all possible, that's the best advice

 

[swathdiver]

Gotta be the battery. They aren't doing the tests properly.

 

[yukonese]

If the battery or cable is bad, how to explain the engine shot off during driving? One needs no battery when the engine is revving, isn't it right?

 

[drakon543]

If the battery or cable is bad, how to explain the engine shot off during driving? One needs no battery when the engine is revving, isn't it right?

not correct in most if not all vehicles anymore i think. back in 01 im not sure it was touch and go. my 97 can run without the battery but ive dealt with vehicles in the same year range that needed the battery in place. your positive cable coming off the battery can have a break inside the cable which can cause problems. same problem with the negative or any grounds for that matter. take the battery to a different parts store and have it rechecked. just incase it was tested improperly.

 

[rockola1971]

To add to the above, if the battery has shorted cell or even partially that becomes essentially a heating element that draws power and your battery is connected to your alternator so the battery can very well draw down the output of the alternator effectively starving the rest of your electrical system. The C and K chassis are very picky about voltages, especially the cluster, radio, auto climate system, BCM and some other electronics. I can tell you for a fact that once my battery got down to 11.6v TODAY the engine started to surge because the ignition system was being starved for power while driving (alternator had zero output). See my thread I created today. Dirty, loose or corroded grounds will mimic a short to ground as far as symptoms go.

 

[HiHoeSilver]

X2 on the cables.

 

[OR VietVet]

X2 on the cables ad I also think that battery is suspect. How old is it?

 

[yukonese]

The Bosch Premium battery is only 3 or 4 months old (with 3 year free replacement warranty). It's not AGM, but should be pretty decent. This truck seems to be very friendly to batteries, the first one, OE AC Delco took 11 years to die, the 2nd one, Die Hard Gold took 7.
Are battery cables expendable? Should be replaced over certain time? The positive one is around $40 from Amazon.

 

[HiHoeSilver]

The Bosch Premium battery is only 3 or 4 months old (with 3 year free replacement warranty). It's not AGM, but should be pretty decent. This truck seems to be very friendly to batteries, the first one, OE AC Delco took 11 years to die, the 2nd one, Die Hard Gold took 7.
Are battery cables expendable? Should be replaced over certain time? The positive one is around $40 from Amazon.

We have seen them commonly begin to corrode from the inside out. It's not always obvious thing to the eye. I'd change them. They're 20 years old, anyways.