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Discussion Starter #1 (Edited)
Something very strange started happening two days ago with the turn signals on my 2006 3.5L Colorado WT. First I noticed that no matter which way I flipped the turn signal level, it was always flashing the left signal, both the actual lamp and the dash indicator. Then yesterday for a couple of hours I lost turn signals completely, but I noticed that if I left the lever right or left the turn signal warning indicator would come on like normal even though no turn signals or dash indicator was showing. Today I'm back to the original problem. Signalling left or right always flashes the left signal and dash indicator.

Has anyone seen this before?

UPDATE: I had a look at the circuit diagram and realized that the turn signal switch is a two-wire device rather than the standard 3-wire SPDT type. Apparently this switch has two resistors inside that both connect on one end to ground. The switch connects the other end of one of the two resistors to the control unit, which detects whether to activate the right or left signals by the resistance detected to ground.

This means that a loose connection that raised the series resistance could fool the control unit into thinking it should activate the left blinker when the right one was selected. Does anyone know the correct resistance readings for the right and left settings?
 

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UPDATE: I had a look at the circuit diagram and realized that the turn signal switch is a two-wire device rather than the standard 3-wire SPDT type. Apparently this switch has two resistors inside that both connect on one end to ground. The switch connects the other end of one of the two resistors to the control unit, which detects whether to activate the right or left signals by the resistance detected to ground.

This means that a loose connection that raised the series resistance could fool the control unit into thinking it should activate the left blinker when the right one was selected. Does anyone know the correct resistance readings for the right and left settings?
Well I'll be damned.
That is a weird arrangement, and an excellent analysis on your part.
Which GM genius thought that arrangement made sense?
Wish I could help.

Does the schematic just indicate resistors with no resistance value shown?
I'll try to find that diagram on my laptop if I have it there..


Where are the wires accessible?
When you say "control unit", does that mean the BCM?
Or is there a separate controller for the turn signals (not likely).


It's Friday, I'll be returning to my truck (I'm out of town, truck's sitting at the airport) hopefully late tomorrow.
Maybe I can find these connections and measure the resistance for you.. would be good to know in any case. If it's the BCM then the wires would be not too difficult to access there at the unit.

.
 

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Discussion Starter #4
Does the schematic just indicate resistors with no resistance value shown?
Yes, got it from the wiring diagrams posted elsewhere in this site. It shows a dotted box around the SPTT switch and two resistors and designates the contents of the dotted box as TURN SIGNAL/MULTI-FUNCTION SWITCH. In the centre position there is no contact. In the left or right positions contact is made with the open ends of one or the other of the resistors. No value is given for either resistor.

Where are the wires accessible?
Haven't had a chance to locate that yet. I wanted to find out the the expected resistance values before pulling things apart.

When you say "control unit", does that mean the BCM?
Yes, the BCM. The diagram shows the switch with two connections. GRN goes to ground (via a connector and then BLK wire) and VIO goes to the BCM (LT BLU after connector). On the BCM the turn signal switch connection is on A45 of C2.
 

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Well if you haven't an answer by Sunday afternoon I'll try to get to my multimeter and make a measurement.

From your description the wires should be accessible at the BCM connectors.
It's under the glovebox behind the kickpanel cover.
 

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Discussion Starter #7
Second Update: I'm pretty much convinced now that this is a grounding problem. I didn't mention it before because I thought they were all isolated, but there are two other electrical problems that started about the same time. First, the blower motor is intermittent, but mostly it doesn't work at all. Note this is NOT the common harness/connector/resistor pack problem that allows the fan to run only on number 4. When it is dead, it is completely dead. Second, both the aux sockets are suddenly dead too. Since the only thing all four circuits (each aux socket has its own fuse) have in common is the G106 grounding pack I figure it has to be to chassis connection for G106.

To summarise, the following circuits all died at about the same time:
  1. Turn signals
  2. Blower motor
  3. AUX1
  4. AUX2

A bad ground would account for the original complaint I posted about since it would raise the detected resistance from the turn signal switch and fool the BCM into always flashing left, or not at all.

I tried unbolting G106 and cleaning up the tab, but it didn't help. I did notice however that when I tightened the bolt by hand with a wrench as hard as I could, the ABS warning came on when I started the truck so it definitely looks like the ground is flaky even when tightened hard by hand. I had to tap the wrench with a mallet to tighten the connection, which fixed the ABS problem, but the other problems still exist. When I have more time I'm going to do a complete grounding tab reconditioning with a new bolt with star washer since the threads had a coating of rust and just tightening the existing bolt isn't improving things.
 

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On an unrelated note, hows the custom planet business?
Done any exciting coastlines recently?
 

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I have had some issues with a faulty bulb..
Probably not causing your problems... But I have seem it cause some weird shit... Even if they appear ok..
Good luck finding your gremlin !!!
 

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Discussion Starter #12 (Edited)
FIXED: Ok, I was right, all my electrical problems were caused by the G106 grounding pack. I now have normal blower operation on all four speeds, turn signals are working properly, and both AUX sockets are supplying juice again.

I will be posting a complete breakdown of how I diagnosed this and the steps I took to fix it complete with photos, but for now here is the high-level explanation. Turned out simply fixing the connection of the big grounding lug on the grounding pack to the chassis as others have reported success with did not work for me. The grounding pack itself was defective, and after disassembling it I can say without reservation that the design engineers who came up with this idea should be shot. If you don't have a problem with your grounding pack yet YOU WILL!

My solution was to cut all four wires entering the grounding pack and crimp a high-quality eye terminal on each one and solder copiously. I also ran an M6 tap into the chassis hole to clean the threads and replaced the rusty bolt itself with a stainless steel M6 x 25mm one. Finally I placed a star lock washer (internal type) between each terminal eyelet and under the bolt head, coated everything copiously with dielectric grease (including the chassis hole), and bolted everything to the chassis snugly.

Everything now works like a charm again. As I said I will be posting soon with photos (including the insides of the grounding pack), diagrams, and an explanation of why I deduced it had to be the grounding pack at fault.
 

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Excellent!

With those troubleshooting skills, perhaps you can advise me about this pain I've been having down all the diodes on my left side..
 

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Is that the grounding pack on the passenger side by the airbox?
 

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FIXED: Ok, I was right, all my electrical problems were caused by the G106 grounding pack. I now have normal blower operation on all four speeds, turn signals are working properly, and both AUX sockets are supplying juice again.

I will be posting a complete breakdown of how I diagnosed this and the steps I took to fix it complete with photos, but for now here is the high-level explanation. Turned out simply fixing the connection of the big grounding lug on the grounding pack to the chassis as others have reported success with did not work for me. The grounding pack itself was defective, and after disassembling it I can say without reservation that the design engineers who came up with this idea should be shot. If you don't have a problem with your grounding pack yet YOU WILL!

My solution was to cut all four wires entering the grounding pack and crimp a high-quality eye terminal on each one and solder copiously. I also ran an M6 tap into the chassis hole to clean the threads and replaced the rusty bolt itself with a stainless steel M6 x 25mm one. Finally I placed a star lock washer (internal type) between each terminal eyelet and under the bolt head, coated everything copiously with dielectric grease (including the chassis hole), and bolted everything to the chassis snugly.

Everything now works like a charm again. As I said I will be posting soon with photos (including the insides of the grounding pack), diagrams, and an explanation of why I deduced it had to be the grounding pack at fault.

Nice work, look forward to the documentation.


Sent from AutoGuide.com App
 

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Discussion Starter #16
Is that the grounding pack on the passenger side by the airbox?
Yes it is. Grounding is one of the most important considerations when replacing traditionally electro-mechanical components with microcontrollers, and the GM engineers completely botched this one. I'll be posting photos shortly of the insides of the one I removed and explaining why EVERYBODY will eventually have a problem with this ill-conceived component.
 

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Yes it is. Grounding is one of the most important considerations when replacing traditionally electro-mechanical components with microcontrollers, and the GM engineers completely botched this one. I'll be posting photos shortly of the insides of the one I removed and explaining why EVERYBODY will eventually have a problem with this ill-conceived component.

I've been planning to replace all the "ground-packs" in the same manner you described.

All auto manufacturers do weird stuff from time to time to facilitate ease of assembly and save a step or two in the assembly process.
Time is money..

The great thing about this site is we have the opportunity to share our experiences as those things become problems so others can learn.
There are some folks here who've given much time and effort over the years to get that sort of information out to the rest.

You've now added a new item for everyone to be aware of and identified a new symptom to watch for (failed turn-signals). :thumbup:
 

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Glad you found the problem! I've had some weird electrical gremlins pop up because of bad grounds before. You did a good job finding this one!
 

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Discussion Starter #19
I promised I would post a more in-depth explanation of how I diagnosed and fixed the turn signal problem on my 2006 Colorado, so here goes. I'm going to break it down into smaller instalments and this first part will explain how I diagnosed the cause of my multiple electrical anomalies and explain how the circuit is supposed to work. First I should point out that I have worked with and around electric and electronic circuits since about 1979, and five of those years were repairing radar and marine navigational equipment on 700 foot cargo ships where bad electrical connections can mean a 9000 ton ship runs aground or collides with another vessel. I know from experience how to make good connections in the harsh environments of vibration and even salt air corrosion.

The first symptom I noticed was that I lost the ability to signal for a right turn. If I tried to signal right OR left, it was always the left exterior and dash indicators that would flash. Later I realized that several other electrical faults had originated about the same time. Here is the full list:

  1. Turn signal always flashes left regardless of left-right position of signal lever.
  2. Blower motor intermittent, but mostly non-functional. A/C working fine.
  3. If blower knob turned from OFF to 1, 2, 3, or 4, turn signal completely non-functional.
  4. Both AUX1 and AUX2 outlets under dash dead.
  5. Occasional error message on startup that ABS was faulty along with ABS warning light on dash.
I had a Haynes manual for my truck but I misplaced it in a move so I obtained the wiring diagram from here:

http://www.355nation.net/forum/atta...ado-w-3-5l-2004-2006-canyon-colorado-3.5l.zip

If you look at the "Exterior Lights Part 1" diagram from that ZIP file you will notice that the turn signal switch has only two external connections, unlike the traditional electro-mechanical circuit that requires three connections. One of the most common engineering decisions when designing with microcontrollers is how to minimize the usage of the limited number of I/O pins available on a chip. The easiest way to accomplish this with multiposition switches is to encode the switch position as a voltage. This is done with a resistive voltage divider. Here's a simple example:



In this case point "1" between the two resistors is at 5.14 volts. Note that for these examples I use the twelve volt battery voltage to supply the circuits, but when your engine is running it will be about 14.5V instead. This doesn't change the principal at work. Now lets change R2 to 1250 ohms:



Now point "1" is at 6.66V. Finally, if you disconnect R2 altogether point "1" rises to 12V. Now lets make those three resistor combinations selectable with the turn signal lever switch:



So now pushing the signal lever for a right turn connects the 750 ohm resistor, for a left turn the 1250 ohm resistor is connected instead, and in the center position the resistor is disconnected completely. This is basically the circuit actually used in the Colorado. Note that the resistance values and voltages shown were chosen by me to illustrate the concept and are not the actual ones used in the Chevy Colorado turn signal circuit.

The design engineers will have chosen "threshold" values for the BCM to interpret the voltage at its input terminal as a signal lever position, for example:

  • 0-6V = Right turn signal on
  • 6-11V = Left turn signal on
  • 11+V = No turn signal on
So in our circuit when the signal lever is pushed right the voltage at the input terminal is 5.14V which is below 6V, so the BCM knows to flash the right-hand signal. When the lever is pushed left the input voltage is 6.66V, which is between 6 and 11 volts, so the BCM knows to flash left. When the lever is in the center position the input voltage is 12V so the BCM knows to turn both signals off. With a good, solid ground this is how it works and all is well, but what happens when the grounding is bad? A bad ground acts like another resistor in the circuit. In the following circuits it is marked as RG:



The value of 300 ohms for the resistance of the bad ground connection was chosen arbitrarily for this example, but could take on almost any value in real life, from nearly zero ohms all the way up to near infinity. As you can see from the two circuits, this time the voltage at point "1" for BOTH circuits is above 6V but below 11V, which the BCM interprets to mean that it should flash the left signal light regardless of which direction you push the turn signal lever. This explains why the first symptom I noticed was that the left turn signal came on even if I was trying to flash right.

Coming in the next instalment... what happens when you ground the blower motor through the same defective ground.
 

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