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2006 chevy trailblazer_ls
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Discussion Starter #1
My heater controls only work on speed 5. Speeds 1 through 4 do not work and causes several warning lights (ABS, SRS, etc.) to come on and start flashing. I change the speed control to 5 or OFF then the warning lights go off.

I did do a search here and saw that the probable culprit was the Blower Motor Resistor. I replaced that but it didn't change anything. I saw that the cable was looking pretty bad like some others have said on here. So, I replaced the cable as well.

Here's the strange part. Once I replaced the cable, I checked the operation and every speed worked just like normal. I gave myself a big pat on the back and said "I fixed it". Parked the truck and went inside. Next morning went out and started the truck, turned the heat to 1 and warning lights started going crazy again. So, now it still only works on speed 5.

I would appreciate any help you guys could give.
 

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2004 gmc
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I'm not familiar with that cable - I thought it was part of a larger, thicker harness that would be much more difficult to replace. But I have the electronic (digital) control so it's all different.

I'd guess when you replaced the cable you jiggled something nearby or beyond the connectors of the part you replaced. And that section has some cut/abraded/pinched insulation that's shorting out to ground. The speed 5 wire must not be damaged, so that's why it works.

Where did this cable come from and go to?
 

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Discussion Starter #3
I'm not familiar with that cable - I thought it was part of a larger, thicker harness that would be much more difficult to replace. But I have the electronic (digital) control so it's all different.

I'd guess when you replaced the cable you jiggled something nearby or beyond the connectors of the part you replaced. And that section has some cut/abraded/pinched insulation that's shorting out to ground. The speed 5 wire must not be damaged, so that's why it works.

Where did this cable come from and go to?
It's the 7 wire harness that plugs into the Resistor. Not quite sure where the other end goes...I think part of it goes back to the speed control knob. It wasn't actually the whole cable, it was about 7 inches of wire going into a new connector. I spliced that onto the old harness. It was the connector that was melted on the old one. It is my understanding that speed 5 is working because that is the only speed that doesn't use the Blower Motor Resistor. I guess it's time to start taking some dash apart. Grrrr!

Thanks for the help.
 

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Discussion Starter #4
Latest Update

I checked all my voltages to make sure the switch was good and that nothing was shorted out. They all checked out good.

Red = Constant 12v
Black = Ground
Yellow (Speed 1) = 12v
Tan (Speed 2) = 12v
Blue (Speed 3) = 12v
Purple (Speed 4) = 12v
Orange (Speed 5) = 12v

I even swapped out the Blower Motor Resistor again thinking that maybe I got a bad one from Auto Zone.

I'm at a loss now. Could it be the Blower Motor itself? I mean speed 5 works, so it couldn't be that, could it? I am open to any ideas that anyone may have. This is really starting to get on my nerves.
 

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2003
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It's the 7 wire harness that plugs into the Resistor. Not quite sure where the other end goes...I think part of it goes back to the speed control knob. It wasn't actually the whole cable, it was about 7 inches of wire going into a new connector. I spliced that onto the old harness. It was the connector that was melted on the old one. It is my understanding that speed 5 is working because that is the only speed that doesn't use the Blower Motor Resistor. I guess it's time to start taking some dash apart. Grrrr!

Thanks for the help.
I'm thinking that you have to look here. You may have to replace the entire harness(es) at each end because something is definitely fried.:m2:
 

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Discussion Starter #6
Blazernut,
Thank you for your response. I actually thought the same thing. The replacement connector came with about 6 inches of wire coming out of it. So, I went about 4 or 5 inches up the old wire and cut it off, then spliced the new connector on. But I get the same symptoms now that I got before I replaced the connector, so I don't think I created any new problem. Plus, I have checked all the voltages (outlined above) and they all check good, so the connector seems to be connected properly. Plus, since the voltages are correct, that would tell me that my Speed Control Switch on the dash is good as well as my fuses, or at least I think that is what it's telling me. Right?

This morning I actually swapped out the entire Blower Motor and still get the same symptoms.

So, if I am correct:
1. The Blower Motor is good.
2. The Blower Motor Resistor is good.
3. Speed Control Switch is good.
4. Connector is good.
5. Fuses are good.

If someone could tell me what else is left, or tell me where my logic above is flawed, I will be happy to check it. I'm at the end of what I can think of.

I'm ready to push this thing off the closest bridge and buy a Honda! Just kidding.
 

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Discussion Starter #7
Finally broke down and took it to the local Chevy dealer yesterday. After almost a whole day of troubleshooting, they couldn't find what is wrong either. They are keeping it through Monday to see if they can figure it out. They said all the voltages and signals were right, so it should be working. At least I don't feel like an idiot for not being able to figure it out myself now. :D

Hopefully, they will find out something Monday.

Stay tuned!
 

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Discussion Starter #9
It's Fixed!

It was the ignition switch. I had read several posts on here about those going bad and I actually thought about that at one time, but it never clicked in my mind that the ignition switch would make the Blower Motor not work on speeds 1 through 4.

The dealer charged me $230 (labor, parts and tax) to fix it. I don't think that was too bad. They did work on it for over 8 hours trying to find the problem. Sometimes you just have to take it to the pros and admit defeat. :(

Thanks for the help guys. Hopefully, this will help someone else in the future.
 

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It was the ignition switch. I had read several posts on here about those going bad and I actually thought about that at one time, but it never clicked in my mind that the ignition switch would make the Blower Motor not work on speeds 1 through 4.

The dealer charged me $230 (labor, parts and tax) to fix it. I don't think that was too bad. They did work on it for over 8 hours trying to find the problem. Sometimes you just have to take it to the pros and admit defeat. :(

Thanks for the help guys. Hopefully, this will help someone else in the future.

That would have been my guess if I had saw your post earlier.. My Ignition swtich went goofy on my TBSS and it caused A crap load of issues.
 

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Discussion Starter #11
That would have been my guess if I had saw your post earlier.. My Ignition swtich went goofy on my TBSS and it caused A crap load of issues.
Oh...so you cost me $230 bucks! Just kidding. :D I'm just happy it's fixed. I was getting tired of either freezing or having a wind tunnel blowing at me.
 

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It was the ignition switch. I had read several posts on here about those going bad and I actually thought about that at one time, but it never clicked in my mind that the ignition switch would make the Blower Motor not work on speeds 1 through 4.
With the benefit of hindsight and the factory service manual, I think I can see how that could happen. There are FOUR separate output wires from the ignition switch that are hot during RUN time. One of them runs the blower motor speeds 1-4 and the BCM. If the ignition switch was dirty or had a high resistance contact, when the blower switch was in positions 1-4, and the blower motor connected, the voltage would drop, and the warning lights could be fed by a detector in the BCM. In blower position 5, the POWER to the blower motor comes from a different path through the ignition switch (perhaps for safety in case you blow a fuse in humid conditions and need SOME airflow to keep the windshield clear!), and the connection through the switch is only used for a low current relay control. So a high resistance ignition switch might work OK to pass 12V through for a relay control, but when the load of a blower motor through the resistor pack is connected, the voltage droops.

Only observation you made I can't explain is the post where you checked the voltages on all the speed wires and found 12V on each of them when you expected to. I can only assume this was with the blower motor or resistor pcak disconnected, so there was no load? If you measured those wires with the load connected, I bet there would have been a lot less than 12V, and the solution might have been less subtle.

But the multitude of outputs (multiple wires for each of RUN - START - ACC) coming out of the ignition switch can certainly cause some very odd symptoms, as we've been seeing reported for years. As the vehicles age, this will only happen more and more, and trailvoy should have a sticky about ignition switches.
 

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Discussion Starter #13
Only observation you made I can't explain is the post where you checked the voltages on all the speed wires and found 12V on each of them when you expected to. I can only assume this was with the blower motor or resistor pcak disconnected, so there was no load? If you measured those wires with the load connected, I bet there would have been a lot less than 12V, and the solution might have been less subtle.
You are right here. I unplugged the connector to measure the voltage. If I had of left it plugged in, I may have seen it.

Live and learn!
 

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You are right here. I unplugged the connector to measure the voltage.
Appreciate the update. After a long career as a systems troubleshooter, I always recommend trying to catch glitches using the identical configuration as when the problem shows itself. Even if that means leaving connectors plugged in, and tapping into the conductor by way of a sewing needle or thumbtack pushed through the insulation. Catch them under load if possible.
 
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