NEED HELP 03 TB - Very Strange Problem with signals

jazmo1

Member
Hello Everyone....My wife's 2003 Trailblazer is doing something very strange. The other day, she was driving it and when she was almost home, it shuddered and then stalled. It started right back up and she got home. The next day, she went and got some gas but noticed on her way home that it did shudder again but didn't stall but she also noticed that the driver side turn signal was blinking real fast. I checked it out when she got home and figured it was one of the bulbs....BUT, I also noticed that the headlights on the driver front were very dull too. Passenger side were all good. So I checked all bulbs and then figured it could of been the taillight circuit board so I pulled that out and here's where it really gets strange. When I pulled out the rear turn signal bulb from the circuit board, the front were still dull and the front directional still blinked quickly. But when I would plug in the rear bulb again, it actually affected the engine idle. Eventually the engine did quit and then would not start back up....as if it was starving for fuel. I figured it must be a ground issue but after checking as many as I could find, and cleaning them up.....it still does the same thing.....dull headlamps on driver's front and quickly blinking directional's on same. Anyone have any other ideas for me to check. I even pulled out the alternator figuring maybe it was shorting out but it still does the same thing even with it out. Any help would be greatly appreciated......THANKS!!!!!!
 

MRRSM

Lifetime VIP Supporter
Welcome to GMT Nation...

It would be very helpful if you had an inexpensive OBD2 Code Reader to pull any Engine Codes out of Memory. Focusing on the most important of the problems you mentioned... The First Guess with this "shudders to a stall" symptom would be to perform a very simple repair:

Clean the Throttle Body.

What happens is that over time, Dirt and inhaled Engine Oil from the PCV tends to collect and Gums up the edges of the Brass (or Aluminum) Butterfly Plate in the Throttle Body, causing it to stick inside of the Venturi either a little open or closed from time to time when the Engine sits at idle, inviting the engine to stall.

If you follow Drew's (@MAY03LT) Instructions in this video using CRC Throttle Body Spray Cleaner (NOT Carburetor Cleaner or Brake-Kleen Spray) it will be an EZ thing to try doing first:


This one has Good Instructive Value as well:

 
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Maverick6587

Silver Supporter
I'm guessing a Class 2 data issue. I'm checking the wiring diagrams to see how those two systems could be tied together, other than probably the BCM.

Edit: Other grounds that should be checked and cleaned while I try to figure this out.
Lower Left B pillar (near the rear fuse box)
There should be a ground behind the driver's side, if not both of the taillights
I think there's one more ground inside the lift gate as well for the lift gate module.
 
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Maverick6587

Silver Supporter
The grounds that the throttle actuator and the left rear tail lamps share are the Lower Left D Pillar (G401) and Lower Right D Pillar (G402). Try cleaning those and see if that fixes it.
 
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jazmo1

Member
Mooseman & Maverick6587......Thanks! I appreciate all the info. I will definitely check those over the upcoming weekend. I did forget to mention in post that I do have an OBD2 tester and no codes were present, not even any pending.
 
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jazmo1

Member
Does anyone have a diagram showing where the grounds are? When you say Lower Left D Pillar (G401) and Lower Right D Pillar (G402) and Lower Left B pillar (near the rear fuse box) .....how do I know which is which and where they are? Thanks in advance!
 

MRRSM

Lifetime VIP Supporter
 
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jazmo1

Member
Thanks a bunch for the diagrams.....I'm going to check the truck out Sat. & Sun. and hopefully figure this out.
 
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jazmo1

Member
I've got more checking to do but I did discover something kind of weird. My wife always leaves the headlight switch to the "Auto" daytime / evening running lights setting. If I turn that setting off so the headlights are NOT on, the left signals blink properly. But even turning headlights on manually, the left signals blink very fast and left headlights are dull. Could this possibly be a faulty headlight switch?
 

Mooseman

Moderator
I doubt it because all it does is send a signal to the BCM which then activates relays.

Sounds more like a bad ground. Another thing to check is all the bulbs themselves. There have been instances of filaments breaking inside the bulb shorting to the other post and causing all sorts of weirdness, like flashing all the parking lights. I'd replace all of them just in case.

Edit: Moved to proper section and title changed.
 
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jazmo1

Member
Headlight switch is not the problem......changed out with known good one and still does the same thing. Also, I did check and clean grounds 401, 402 & lower left "B" pillar ground....all were clean & tight. I will continue to check other grounds on underside as well as engine block grounds. Also will recheck all bulbs.....THANKS!
 

MRRSM

Lifetime VIP Supporter
While this Video is dedicated to those who perform HID Modifications... and How to SAFELY Shut Off DRLs in the Trailblazers-Envoys... It DOES contain some additional Diagnostic and System Operations Information as broken down by Drew (@MAY03LT) that should explain much of what you have observed with the appearance of having "dull beams" in the opening minutes of this presentation:

 
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jazmo1

Member
I am checking this vid. out right now. Thanks! I should also point out that last evening, I did also discover that when the headlights are turned on manually, the directional does blink properly BUT the left headlamps are still dull.
 

Mooseman

Moderator
Check the wiring and connectors inside the headlight to the bulbs. Although haven't heard of it lately, they do sometimes melt down.
 
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jazmo1

Member
Will do. I didn't get a chance to look at it yesterday but plan on doing a good look at everything this afternoon. Thanks!
 
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jazmo1

Member
I finally got a chance to check most other grounds as well as bulbs & sockets and after all of this, the truck still does the same thing. I have no idea what else to check. Any other ideas what to look at or check out?.....I'm really perplexed at this problem because it came on quickly and I've checked so many things.
 

Maverick6587

Silver Supporter
At this point, after checking the grounds. I would treat this like a parasitic draw test. Remove a fuse one at a time and see when the driver's side headlight goes to full power.
 

budwich

Well-Known Member
I finally got a chance to check most other grounds as well as bulbs & sockets and after all of this, the truck still does the same thing. I have no idea what else to check. Any other ideas what to look at or check out?.....I'm really perplexed at this problem because it came on quickly and I've checked so many things.
OK... but where are you at exactly? (truck does the same thing)? You did some stuff (headlight switch, grounds and power checks).... then after this and some posts, you get "enlightened" with an "ah ah", signal indicators are normal. Look at the original post and now state what you are and aren't seeing or running with (truck stutter, etc). Having said that, IF the only issue you have is "dull left headlight" then so beit and that can be worked on although give exactly what operations you have checked to confirm this problem. AND IF this is true (one weak low beam), get a meter, locate the low beam fuse for each side, remove the fuses. Set the meter on dc volts and measure the voltage at the fuse points (two for each fuse), record the result. Now set the meter on resistance and measure the resistance ON ONLY the side that read ZERO VOLTS. STOP... IF the voltage measurement had no fuse point at "ZERO". Post your results.
 
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jazmo1

Member
This is where I am currently at----When just the turn signal is on (no headlights), signal blinks properly. But, as soon as headlights are turned on, signal blinks fast and left headlights are very dull. All lights on right side are good. Hazard lights also work properly. The weird part, as mentioned in OP is that the truck initially had stalled. Wife started it up again, and made it home. The next day, on her way to get gas, she realized that left signal was blinking fast. When she got home, I checked figuring it was a bad bulb. After checking bulbs and finding none bad, I figured maybe the tail light circuit board was bad. With truck running, and signal blinking fast, I pulled out rear signal bulb from circuit board....idle changed a bit. Then I put bulb back in socket and idle changed again. I tried pulling out and placing back in a few more times and idle kept changing. It eventually stalled and would not start back up. Definitely seemed to be starving for fuel. So along with the other suggestions and ideas to check....that is where I currently am with this. Do you know if any grounds on the right side of truck, like on the inside or underside, effect left side systems (primarily left side headlights, signals, fuel pump or relay, etc...)?
 

MRRSM

Lifetime VIP Supporter
This is NOT a "Spot On Thread"... but there are enough similarities in the discussion that might contribute to figuring this problem out:

 
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jazmo1

Member
MRRSM....I did see that post prior to my post and yes, very similar. I too wish that that person who discovered his problem would have said which location it was at. I know several others towards the end of that post were interested in where it was specifically as well. Budwich I will try your test / checks over next few days. Probably not until Monday as I am required to work to help make medical supplies for this horrible virus outbreak. You guys all stay healthy & safe out there!
 

MRRSM

Lifetime VIP Supporter
1.jpg
 
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jazmo1

Member
The G107 ground I did unbolt, and clean up (although it really wasn't too bad) and then re-bolted it up. I did inspect the other ones as well (G108, G109 & G110) which all looked decent but I didn't actually unbolt them because it appears that these grounds don't have anything to do with the headlamps and/or signals. At least as far as I've seen.
 

MRRSM

Lifetime VIP Supporter
What a Helluva PITA this Problem is! :Banghead:
 

Mooseman

Moderator
Try this. With the headlights on and turn signal on (fast slash), pull the connector off the headlight bulb (on the bulb, not the pod's main connector). What happens? With the bulb still discoonected, turn off the headlights. What happens? If still hyperflashing in both tests, I'll bet it's a ground issue and the bulb is being used by the turn signal as its ground.
 

Maverick6587

Silver Supporter
I agree with mooseman on this! This is 100% a grounding issue, unless you have LED blinkers? Did you switch to LED blinkers?
 
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jazmo1

Member
They are the regular bulbs. But I also agree.....this has to be a ground issue. I just have not been able to locate it. I'm going to do the test & checks that Mooseman & budwich suggested above on Monday and will update then......Thanks all!
 
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jazmo1

Member
Hey everyone! Just a little update. I did a little more checking and found the following. When the headlights are off (auto. or manual)....the turn signals work properly and vehicle starts & runs fine. If I turn headlights on, whether manual or auto. and then turn on left side directional's , they blink very fast and vehicle eventually will stall. Right side works fine. But anytime headlights are on, left side are always dull, even when directional's are not on. I did check other grounds as well as bulbs and plugs but still haven't found the cause. This has to be a GROUND issue but no luck yet finding it. I will continue to look and will update as I find out anything. In the meantime, everyone stay healthy & safe during this horrible crisis!
 

TollKeeper

Well-Known Member
I would also like to suggest checking the ground strap thats right inbetween the battery and the front main fuse box and the inner fender. That should be the supply ground for relays in the fuse block. I doubt its bad, as there isnt much draw/current on it, but you never know. And every time the battery is taken out, you run a 50/50 chance of unbolting it thinking its the crossbrace bolt (dont ask me how I know LOL).
 

Blckshdw

Moderator
Just for my own curiosity... Can you try the left turn signal when the parking lights are on, but low beams are still off, and see if it behaves the same way, or flashes normally? If they still hyperflash, I would try removing the 194 side marker bulb, and retry. If the flashing goes back to normal, then either the bulb, or possibly something wrong with the socket
 
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jazmo1

Member
Blckshdw & TollKeeper......I tried left turn signal with just the parking lights on and headlights off and signal does blink normally. As soon as headlights are turned on, turn signal blinks fast and left headlight is dull. Left headlight is also dull when left turn signal is off. I did check the ground wire that goes from negative battery cable and branches out to inside fender, and to under hood fuse box and all was good. That same cable also goes to engine block and a grounding spot under wheel well near strut assembly.
 

christo829

Well-Known Member
Just for the sake of covering bases, as Mooseman suggested in post #14, did you check the wiring inside the headlamp assembly? Not the sockets for the bulbs, but the wiring going from the harness to the headlamp itself, and then the wiring from that plug in the headlamp assembly to the individual bulbs?

I didn't see where you had checked that, and my apologies if you did and I managed to miss it.

Good Luck!

Chris
 

Blckshdw

Moderator
OK, next idea, disconnect the driver's side low beam bulb, then turn on your headlights and activate the left turn signal. If it flashes normally, then the problem is on the ground side of the low beam circuit. If it continues to hyperflash, then we know hot signals are getting crossed somewhere. That should help narrow down what wiring or modules to troubleshoot a little more.
 
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jazmo1

Member
christo829.....I did check the wiring to the individual bulbs as well as plug in a known good headlight assembly and didn't find anything wrong with them. And all the socket ends look good too....no corrosion or melting as I have seen on other Trailblazers in the past. I'm going to try Blckshdw's suggestion over this weekend and see what happens.....I will post a follow up with results. Thanks!
 

MRRSM

Lifetime VIP Supporter
Recently, @Mooseman found an EXCELLENT Deal on an After-market Power Probe (discussed over in the Tool Talk Thread, Post # 540) that could prove very useful in running any Broken Wires or Open Circuits involved to ground in your present predicament:

MOOSEMANSPOWERPROBE.jpg
 

Mooseman

Moderator
Yeah but unfortunately, Amazon, at least here in Canuck land, has been slow with shipping on most items. If non-essential, it can take a month or more.
 

NJTB

Silver Supporter
Some of the Amazon warehouses have had employees test positive for Corona 19. When that happens they close the warehouse for sanitization (several days).
They also go back 72 hours on the security tapes to look for anyone who had been within 6 feet of this person and tell them to stay home.
The world's really changed in the last 6 weeks.
 

DavidHendrix

New Member
I had to run a ground from the Battery to the frame direct to stop the same thing after I had checked all the other grounds. This was on a 2001 S10
 

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