Replaced battery and starter already, thought this issue was behind me. Today the Hummer won't start again (after working fine for weeks). The key will turn, the head unit gets power, but when I try to crank it, the check engine light flashes and it makes a clicking noise. Is the alternator next? I will check the alternator and battery with a multimeter but other than that is the clicking indicative of anything?

 

Low voltage to starter...check battery voltage...make sure terminals are clean/tight.

 

try swapping the main relays like starter or mains

 

Check starter connections for corrosion or if they are loose

 

You most likely have a parasitic drain, what you describe is a classic low voltage symptom. Do you have any aftermarket electrical stuff on your H2, like lights, stereo or remote start/alarm? If so I would look at those as the culprit first.

 

what is your battery voltage at. i know on older GM vehicles sometimes the internal alternator exciter relay would short and cause a drain. but i am not sure if the hummer ones are designed like the old 70's to early 90's alternators. back then you would look for current drain then whack the alternator. if the drain went away you knew it was stuck.

 

This whole situation is so strange...here's what's happened so far...

Hummer kept being sluggish to start and eventually battery died. I bought a brand new battery and it was still sluggish to start. I replaced the starter on Dec 3rd and then it was starting like it was brand new and I did not have any battery or starting issues for weeks.

I last drove the hummer on Sunday February 2nd and it was fine and no sign of battery problems. It had also been working perfectly since Dec 3. Then on Friday February 7, I attempt to start it and it just clicks.

This morning I went out to try swapping the relays and the truck was completely dead, not even clicks now. I checked and the voltage for the battery was 1.1 lol. Tried jumping it with another truck and it would crank but wouldn't start, the dash gave a warning "battery not charging." I got the battery fully charged from where I bought it and I replaced the alternator.The hummer starts up perfectly now. There used to be a squealing noise when idling that now seems to be gone, not sure if that's because I put the belt on better or maybe the old alternator made that noise because it was going bad?

Another interesting turn of events... All my roof lights (the off road ones) no longer work, when I pressed the switch it briefly made a buzzing noise under the hood and never turned on, buzzing noise now went away. I'll have to investigate it further tomorrow. Maybe when the battery died it blew the fuses somehow for the lights? I don't think there is a parasitic draw because it drove perfectly for 2 months then all of a sudden died in the span of a few days? I really don't know why my lights stopped working though. Oddly enough the light bar on the grill does work, just not the roof lights.

 

False alarm on the lights. I'm retarded , when I took the fuse box lid off yesterday it accidentally pulled both of their plugs out of the relays (the wires run right over the lid to reach the battery). So hopefully the new alternator will finally solve all my problems. Strange that both the starter and alternator went within 2 months, but the truck is 16 years old

 

If you haven’t already, pull the fuse to the OnStar, a lot of people used to find the OnStar module was putting load on the battery with the vehicle off. I assume you don’t use it so it’s good insurance to have one less module that could cause problems.

 

Yea I actually have this problem in my 03 h2 as well, I have to make sure I start it every couple of days or atleast once a week to make sure the battery doesnt get so low it dies