I have a 1998 Blazer LT with over 200,000 miles (yeah, alot). I have been having some very puzzling electrical issues. I have taken it to the dealer (reluctantly, but after I had done as much research and troubleshooting as I could stand) and they found a ground bolt in the electrical compartment that had rusted off completely and that the ignition switch was bad. They fixed the bolt and I replaced the ignition switch ($250 to replace a $60 switch was a bit much for me to cough up). Unfortunately this did not fix the problem. I did a voltage check at the Instrument Panel Fuse Box and found that all circuits had power. I have also checked out the multifunction switch and that works just fine as well. Here is the list of items that aren't working:

- HVAC Blower Motor will not work (however, it does sound like the vacuum lines are actuating the shutter doors so I don't think the switch is bad)
- Front Wipers will not work (I have replaced the pulse control board which had no effect)
- Fuel Gauge does not work (It did not show the "classic" symptoms of erratic operation, it just quit working)
- Temperature Gauge does not work (Same as fuel gauge, just quit working)
- ABS Indicator Light is on
- Battery Indicator Light is on
- 4X4 Selector Switch does not work
- Gear Indicator Light does not work (Display does show the PND321, but gears are not highlighted when key is in RUN position, however, the gears are highlighted when the key is in the ACC position)


All of these failures happened all at once when the Front Windshield Wipers were turned on. At first it was random andsometimes shutting the vehicle off and starting back up would reset it and everything would work. I have checked the interior grounds behind the instrument panel at the firewall and they look as good as the day they were installed. There is no corrsion and the connections are very tight. The wires (what I can see) are in perfect condition.

I have an Alldatadiy account and have been trying to determine if there is a common harness or wire that would be the culprit here, but I haven't been able to find it yet. If anyone has any idea of what might be going on here I could use the guidance. Any and all advice would be great.

Great site by the way, lots of good information is in these threads.

 

Just an update, I have tried replacing the Body Control Module which did not fix the problems. I wish it was only that easy.

 

Not too be impatient, but does anybody have any ideas? I really don't want to have to take the blazer to the dealer again...

 

My gut feel tells me you have an electrical grounding issue. The age and mileage on the vehicle suggests that a ground strap may have given up the fight. Unfortunately, I don't know where all the grounding straps are and sometimes I just find them when and where I least suspect them. Considering all the various "failures" that you are experiencing, I can't believe that it would be a whole combination of fuses, relays, etc. that all STB (S--- the bed) at the same time. I was reading my Haynes manual last night and it states that electrical problems are real buggers to trace down, BUT electrical problems are actually pretty simple if you don't lose sight of the fact that an electrical failure is simply a disruption of a 12V circuit from the battery, through the failed part(s), back to ground. I would suggest that you start wiggling the various wire bundles (under the dash and under the hood), one at a time and re-checking your list of failures. If you find that moving a wire bundle or wiggling an electrical connection helps some or all of the problems go away, then at least you have a place to really concentrate your efforts to finding maybe a corroded wire or a plug or a lost/broken ground path. Patience is the key word here. Good Luck.

 

Thanks junkmonkey, I did do the "wiggle" test on the harnesses under the dash that arestrapped to the firewall under the carpet. I did, however, have a breakthrough last night.

I didn't mention this, but I checked the power wire for the cruise control module (another component that wasn't working that I didn't mention in the first post) and there was 12 Volts being supplied to the module. However, when driving the vehicle, the cruise control would not activate and engage. With this information I got to thinking again about the Body Control Module. It seems like the BCM is not sending out the control signals. So, with this, I tried installing the BCM I bought from a junkyard again just to see what would happen. (I did try installing this before, but not after I replaced the ignition switch.) I went through the passlock relearning process. After that was complete I restarted the vehicle and noticed that everything was working for about a minute and then went back to the condition with the multiple failures that I described in my first post.

So, to me, it sounds like there is something with the Body Control Module that is not right. Would anyone happen to know if there is a ground specific to the BCM or a dedicated power wire to the BCM that I could test the incoming voltage on to see if it is getting the correct voltage?

 

Hmmmmm....everything was working, then it suddenly stopped?!? That sounds like a flaky relay to me. If I'm not mistaken, modern vehicles use self resetting relays. If a relay is going bad, it could reset itself upon Ignition Off / On, then go flaky on you as it continues to draw current. It might be worthwhile to either buy a new relay and test/replace each existing relay (one at a time) to narrow down the hunt. BCM is also a good suspect but I'm not well versed with it's functions at this time. Good Luck with your quest.

 

Another update, I think I have found the problem. There is supposed to be a 5 volt reference signal supplied to the Body Control Module through pin A4 of the C3 (purple) connector. I used my multimeter to measure the voltage at this pin and it read somewhere around 150 millivolts (basically nothing) with the key in the run and off position. I did find that on the C1 (blue) connector for the Engine Control Module pin number 30 is a 5 volt (VSS high) output. I thought that this might be the 5 volt reference supply for the BCM so I did a continuity test from this pin to the pin on the BCM connector. There was no continuity.

Does anyone know if this is the 5 volt signal from the Engine Control Module is the supply for the BCM? Also, is there any 5 volt supplies around the Body Control Module that could be tapped into to test to see if this is the problem. I am thinking I might try a 5 volt power supply of some sort to test it as well. I will post if I find anything out.