I have had and love my 1999 Vortec V6 Blazer for over ten years. Recently, odd things have been happening, First my fuel gauge and temperature gauge froze in place and haven't moved since. Then cruise went out, now heater controls no longer work either. I was fine with these issues because I could still monitor my fuel via the overhead display that shows miles left in tank. No biggie.

Then my headlights started not coming on, I had always left them in automatic mode, but sometimes now they wont even come on in manual on position. Sometimes a smack on the dash or a light kick at the bottom of the sterring column would cause them to come on, now it is just hit or miss whether they will work or not.

And finally, the alternator only charges some of the time now. I had it tested in the car and they said it was bad so I replaced it, but the problem continued. I replaced the battery just because it was pushing 3 years old but that didn't solve it either. I'm thinking the ECM needs to be replaced, or possibly could be in the ignition switch? Figure I would consult with some smarter folks before I throw more money at the problem.

Thanks in advance for any help,

Jason

 

Highly unlikely that the PCM has anything to do with it, (they rarely fail). When seemingly unrelated multiple electrical stuff starts acting up, it's usually due to a poor ground connection. Start by taking all of the cable connections apart and cleaning them. Take the rubber boots off of the battery cable ends and clean the terminals. Both ends of all positive and negative battery cables. Pay close attention to where the battery negative cable attaches to the engine block AND the braided body ground from the rear of the right cylinder head to the firewall, near the blower motor. All connection need to be shiny clean, and tight.

 

Thanks for the advice Captain Hook. The late reply is due to the fact that I've been in Coast Guard Captains license training all week, I'll be Captain Jason in short while. I am planning to open her up and check the cables as you recommend. I can live with everything but the headlights and alternator. :-) From the sound of it, getting the grounds clean may solve all of it at once. I will report back when finished, and thanks again.

 

Congrats Captian! We'll be waiting for the results.

 

Well, after 15 days offshore, I got back on land and made "some" progress. I cleaned up the battery terminals and the chassis grounds under the battery. I cleaned the engine block ground on the front of the block. I cleaned the braided ground that comes up from the back of the cylinder head to the firewall, but only on the firewall end. I wasn't able to get tothe cylinder head end easily as the cylinder head allmost butts up directly against the firewall.

The result: Alternator is charging, or at least it did on this start up (it has intermittently worked before) but I'm hopeful. The bad news is that the headlights still won't come on, the fuel and temp guages still don't work. We did regain the heater controls, haven't tried the cruise control but it might work, it seemed to leave at the same time as the heater.

Any tips on how you access the firewall/body ground at the cylinder head would be appreciated. Honestly all of the connections looked great except on the battery itself, they were powdery white, more so on the + side.

Another thought, is there anything right at the firewall under the brake pedal that would affect head light function? When they started getting intermittent, I could just tap my foot around under the brake pedal and they would come back on. If it keeps charging and i can get the lights working, i'd be good. Just can't live without my headlights. I'll report back if it keeps charging or if this was an intermittent thing.

 

Any luck on finding the issue? JW cause im having a similar issue.

 

No, cleaning the grounds seems to have fixed the alternator charging problem but the headlights are still not working. My Blazer has spent much of her life on the beach so I'm sure there is some corrosion somewhere that is not normal, but I sure wish I could find the cause of the headlights not coming on.

 

Update. The headlight problem was fixed by re-doing a ground under the dash on the drivers side. there is a white connetor box and the center connector is a ground. I pulled it out, cleaned it up and reinstalled it and the headlights have worked since. Oddly enough, the power seat wouldn't go backwards before but now it will after this fix. I am converting the alternator to from pulse width modulation to voltage maintenance mode tomorrow, which should get back on the road again.

 

Captain Jason! With regard to switching to voltage sense: Wherever you connect the voltage sense wire is where the alternator will maintain voltage. The TSB instructs to connect to the rear of the alternator. You'll find it performs much better if you connect to the battery feed at the underhood fuse panel, where most accessories get their feed