I have a 2001 GMC Jimmy that suddenly began acting up, and I believe it's a bad ground. But I don't know where to begin to diagnose this. I have some codes but they don't involve anything electrical. Something is sucking power, and ultimately killing the battery it seems, 5W at a time. It'll crank, drive, then start stuttering and acting like it has a clogged fuel line, But I know that's not it - that's just how it acts. I've hooked it up to a charger and let it absorb as much power as possible. It stops at 5W which is why I say that.

When I crank it, and leave it running, the battery light flashes at odd intervals.

When it finally conks out the gauges drop to 0 except the oil gauge. It'll then refuse to start. It'll give a machine gun noise for a bit, but eventually croak for good.

The battery is a pretty new DieHard. I live in Louisville KY, a place with salt and snow and I know after time that'll cause issues. I only have 134000 miles though.

I have an multimeter and code reader. But I don't even know where to start to find this.

Does anyone have any knowledge or experience with such a thing? I need to lay out a plan.

Thanks in advance ! !
Michael

 

Bad grounds are rare. Not impossible but not the most likely. Nothing wrong with checking the major ground attachment points visually before we get start:

1. Left rear radiator support
2. Right rear radiator support
3. Left rear engine block
4. Right rear engine block

Assuming this does not fix your problem:

1. Charge the battery, then turn the lights on for 20 seconds to knock the surface charge off, then the light back off and measure the battery voltage at the terminals
2. Turn the truck on and remeasure
3. See how low it drops while cranking
4. What is the voltage with the truck running

Meter black lead on battery ground for all measurements


George

 

Hi George - You're always a great help. I appreciate it! I wanted to research and tinker a bit before moving ahead.

I now think it may be a bad alternator. I'm sort of hoping because finding a short or bad ground is daunting to me. Most of my tools are in storage across town to make matters more complicated.

I charged the battery all the way up overnight and the battery will hold a charge. It's pretty new, too, so I don't think the battery's any issue. But when I crank it, the battery light comes on intermittently on the dash, and the Voltage is ~11.6. That's low when running. No codes are present on the OBDII reader. And if I drive it, as I did last night to see what would happen, it drains the battery down to where everything dies and it cuts off completely. Headlights off, instrument panel (besides oil) and so on. I can charge it back up and drive a few more miles until it's drained again.

So I'm going to see if I can determine if it's the alternator before going down the ground/short rabbit hole. Thanks so much for your help!!!

 

Check all your connections at the alternator and back at the battery posts. If everything is clean and tight, charge up your battery, start the truck and measure the voltage on the output. Post of the alternator. If it’s still 11 and change volts then yeah you should get that alternator off and get it to a parts store to test.

George