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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #1
Hopefully someone will be able to shed some light on this... :hail:

Everything started 2 weeks back, front wipers would start to randomly engage while driving, this would usually happen along with the washers. Sometimes they would spray for long time, sometimes just a squirt or none at all. I am not sure if playing with the handle helped anything. It would usually stop after few moves.

Few days back it got suddenly worse and the wipers would barely pause so I took the car to the local "mechanic". He checked the fuses, didn't find anything, told me its the computer and should be serviced at the dealers :worried: I suppose he meant the BCM??

Same day I noticed the head lights would not switch off after shutting the car and waiting some time. Basically they now work when the engine is off, when I turn the key to accy they go off and stay off after starting the engine. Once again, checked all the fuses (under hood, under back seat), replaced head light relay, no change. I recorded voltages on the control leg:

Engine off (lights on)
light knob position: lights auto: 2.6V, Parking lights: 2.6V, lights ON 0.2V

Engine on (lights off)
light knob position: lights auto: 12V, Parking lights: 12V, lights ON 12V

Next day low battery didn't let me start the car, I did notice the battery light and the gear selector were both ON when I opened the door but the light know was on auto! I can now reproduce this, relay in place & night time: open door (battery light and gear selector turns on), close door, turn knob to lights on and back to auto, wait 20 seconds, now if you open the door the battery light will turn on again. When these 2 turn on they will stay on until you turn the knob to ON, or I also noticed that turning the high beams turns them off as well. Weird!
Anyway, replaced the battery because it was already its time but that didn't help in this case. Googled heavily, tested the ignition switch:

With engine off (so the lights are on at all times):
knob on "lights on position": orange 0.2V, red 12V, light yellow 0.2V
parking lights position: orange 2.6V, red 12V, light yellow 2.6V
lights auto position: orange 2.6V, red 12V, light yellow 2.6V
The last cable in the row is a bit darker than the light yellow and it's ground, didn't test the 5th cable (orange?) which sits in the second row.

I just remembered about this yet another weirdness - this has been going on for months, when turning the engine off the doors would get automatically locked 90% of the time. Note that changing the gear to/from park controls the locks just fine, as well as my remote control and door controls.

Finally, I will have access to exactly same model of TB in a few days, can I use it to test something? BCM? ignition switch?? I'm not a professional as you might have guessed by now but I would really like to avoid the dealers place :sadcry:
 

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2008 chevy
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62 Posts
may need to reprogram the computer, had a few light/code problems a few months ago checked all the code problems ever thing checked out ok still having lights/code had the computer reflashed, 2 months now no more problems
 

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2004 gmc envoy_slt
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2,470 Posts
The BCM does not need or does a reset. There is more likely a poor electrical connection or corrosion somewhere, and finding that will require time and experience.
 

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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #6
I've heard unplugging your bcm for about 30 min-1 hour will reset it and might fix the issues.
Thanks for the suggestion, tried it but didn't work.

I was wondering if I could connect a different BCM to see if that is the culprit. The other BCM would come from same year TB but it has 4WD, mine is just 2WD. So would that be safe or better not try? :undecided

Is reprogramming the BCM a complex/expensive task or is it similar to flashing a firmware on "home" electronics, 5 minutes and good to go?
 

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2004 gmc envoy_slt
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2,470 Posts
If you have access to another BCM, give it a try, you can't hurt anything.

BCMs can only be programmed by the dealer and they usually charge $100+ for this.
 

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2004 chevy trailblazer_ls
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333 Posts
You may have a few different issues going on. The wiper problem MAY be the wiper control module itself (it's in the cover of the wiper motor) and will give symptoms like you describe.
See if you can track down a electrical diagnosis chart and troubleshoot it.
 

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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #9
Thanks for all your suggestions. So I went and swaped the BCM and that didn't help at all. In fact, the next morning I couldn't crank the engine, it was dead silent. I am not sure I heard the click... Power was there, everything worked, except the engine. Left it like that and when I came from work I tried... and it started right away. Moody rusty?? :weird:

Went to investigate more. Replugged the washers and found one of the to be constantly on with engine off, by fuse box it seems to be the rear one. Strange, since it was the front one which was going crazy before and I never saw anything wrong with the rear one. Didn't have water to test :duh:

I am afraid EnvoyBoy2004 might be right about the electrical issue, not sure I will be able to track it but I'd like to have a go. Any other suggestions?
 

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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #10
Just wanted to update that I completely opened up the fuse box and found it in very good condition, cleaned it and put it back together and I'm still having the same problems.

I will check the wiper control module but I'd really like to sort out the lights first. When I connected the B+ pin of the light module with the pin going to the lights they worked so I assume the section from fuse box to the lights is working fine. Since I already checked a second BCM I guess we can rull that out so what's left? the light switch which nobody is suggesting and a wire issue. I can't rule out the wire issue but I've looked at some parts of the wires and they seem to be in good condition.

Can anyone suggest how to test the light switch once I get it out?
 

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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #11
I seem to have a short to ground somewhere between under the steering wheel and back fuse box. I cut and run a new wire from under the steering wheel to the back fuse box and my lights issue is fixed. hooray! Going to work on the wipers soon.

Just was curious how to get under the carpet to look for the short since I don't see any openings anywhere. Does it require removal of driver seat or the central panel (storage box)?
 

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2006 saab 9_7x
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6 Posts
I cut and run a new wire from under the steering wheel to the back fuse box and my lights issue is fixed. hooray!
That's a pretty bright idea! I'm gonna borrow this for my issue..

The harness you're talking about in the rear fuseblock is the body harness I believe, it runs down the doorsills from what I can see; but it doesn't control the headlights so I'm confused there. I'll look into this more tomorrow.

The shop manual says you need to remove the seats, center console, and even the door sills to get that carpet up. Sounds like a freaking headache, I'd see if you find where the voltage drops to narrow down what area you need access to.
 

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2005 chevy trailblazer_lt
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Discussion Starter #13
Thanks for your feedback.
I took a closer look, noticed an ugly screw holding the console's left side panel and an even uglier one on the right hand side. Wow, how did I miss them before :duh: I removed the inside of the storage compartment which allowed me to peak inside further. Definately I was not the first person to look in there. Noticed some srews missing and lots of trash. Someone did some bad job around this area and I am pretty sure my wire business is connected with that mess. I stopped to read on about the center console, any tips on removing it?

I do believe a thick bunch of wires is going in there somewhere, since this is how its directed from under steering wheel to the right and behind the plastic cover. Looking from the back fise box, the bad cable also appears to be coming from the center of the car, rather than the side.

I tried to use a short finder but did not get any response, maybe it's too deep for the sensor to pick up the signal...
 

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2006 chevy trailblazer_ls
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672 Posts
These electrical issues in your T.B. have been discussed here since August.

Not easy for a novice to diagnose, but a dealer could have addressed it for certain.

You need to purchase a GM TRAILBLAZER shop manual to lead you correctly into your wiring maze.
 

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2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #15
These electrical issues in your T.B. have been discussed here since August.

Not easy for a novice to diagnose, but a dealer could have addressed it for certain.

You need to purchase a GM TRAILBLAZER shop manual to lead you correctly into your wiring maze.
I don't have much free time and I already had a workaround with the bypass cable, so I wasn't really in desperate need to fix this, especially at the stealers :nono: finally, its so much more fun to do it yourself and get to know your car :)

Anyway, just wanted to say that I found it and it was that ugly screw. Can you imagine it went through that thick bunch of cables which runs just to the right of the driver seat (underneath the carpet) and probably touched the body at the end since it was like 5cm long. :eek::eek::duh: unbelievable...

Thanks again to All for your suggestions and comments!
 

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Registered
2005 chevy trailblazer_lt
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11 Posts
Discussion Starter #16
Oh, and as for the wipers this fixed it as suggested previously: ACDelco 19120931 GM Windshield Wiper Motor Pulse Board And Cover

Had lots of fun removing the wiper arms :mad: but in the end I succeeded :woohoo: 2:0 for me!
 
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