Power seat/adjustable pedals not working

Tiny
CHRIS EMERY
  • MEMBER
  • 2007 GMC YUKON
  • 6.2L
  • V8
  • AWD
  • AUTOMATIC
  • 151,000 MILES
I have read the posts here about this problem. Driver power not working. Adjustable pedals not working. I have pulled off the power seat switch and there is some power to the switch.
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Sunday, February 26th, 2017 AT 11:20 AM

16 Replies

Tiny
CARADIODOC
  • EXPERT
What does "some power" mean? Check the red wire to the power seat switch. It should have 12 volts all the time. To be most accurate, that should be measured by back-probing the wire with the connector plugged in. Alternately, a test light works better for this test, but if all you have is a digital voltmeter, that will be okay too.
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Monday, February 27th, 2017 AT 1:57 AM
Tiny
CHRIS EMERY
  • MEMBER
Red does have power. What I meant by "some power" was there was not any power to any of the other wires, just the one.
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Monday, February 27th, 2017 AT 9:09 AM
Tiny
CARADIODOC
  • EXPERT
Dandy. Now the potential problem is there can be a break in the wire with just one tiny strand left, and that is enough for a digital meter to detect 12 volts, but it's not sufficient to pass the amount of current needed to run a motor. If you tested the wire with a test light, those draw more current and we can believe it. To be safe, and to insure we are not glossing over a clue, test that wire while the switch is plugged in and you activate one of those switches. Either that 12 volts is going to stay there, or it is going to drop close to 0 volts. If it drops to 0 volts, we have to treat that red wire as not having 12 volts. This may seem like overkill, but it is exactly the type of mistake that sends experts down the wrong path.

There are actually 12 switch contacts built into the driver's seat switch assembly, and we know they did not all fail at the same time. Also, there are three motors, and they also did not fail at the same time. That only leaves the ground circuit as the source of the defect. We can use any of the three circuits for testing. I am going to pick the forward/backward switch, just so I can tell you which wires to probe. These next tests must be done with the switch plugged in.

Back-probe the tan and the light green wires. Both will have 0 volts when the switch is released. Now, while watching one of those wires, move the switch in one direction, then the other direction. In one of those directions you should find 12 volts on the tan wire, and 0 volts on the light green wire. In the other direction, you should find 12 volts on the light green wire and 0 volts on the tan wire. If you find 12 volts on both wires at the same time, regardless of which way you push the switch, the ground wire has a break. If that is what you find, measure the voltage on the black wire while the switch is pressed and you have that 12 volts on the tan and light green wires. If you find 12 volts on the black wire, there is a break in that wire or where the wire is bolted to the body, near the base of the left "B" pillar. If you find 0 volts on the black wire, either there is break inside the switch, (very uncommon), or that terminal is not making good contact.
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Monday, February 27th, 2017 AT 9:55 AM
Tiny
CHRIS EMERY
  • MEMBER
12+ volts on the tan wire when switch pushed forward. 12+ volts on the green wire when pushed to the rear. 0 on both when idle.
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Sunday, March 5th, 2017 AT 6:55 AM
Tiny
CHRIS EMERY
  • MEMBER
Seat Switch plug
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Sunday, March 5th, 2017 AT 7:21 AM
Tiny
CARADIODOC
  • EXPERT
What did you find on both wires when the switch was pressed one way? If you found 12 volts on both at the same time, you should have also found 12 volts on the black wire. Check that black wire. If you see any voltage, even if it's less than 12 volts, (but not 0 volts), there is a break in that black wire.
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Sunday, March 5th, 2017 AT 1:14 PM
Tiny
CHRIS EMERY
  • MEMBER
The current alternated between the two seat switch positions when activated. When you say black wire, do you mean the gray with black
Stripe. When I connect the purple + and gray /black (-) I get 12+. Is this correct in what you asking?
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Sunday, March 5th, 2017 AT 3:14 PM
Tiny
CARADIODOC
  • EXPERT
There's no purple wire on my diagram. I suppose there could be a white tracer on the black wire, but that isn't shown on my diagram.

To double-check, your test light clip lead or meter negative probe should be on ground, meaning a paint-free point on the body. This way we're taking voltage readings AT a point in the circuit, as opposed to between two points. Those are just two different ways of doing this, but we have to be sure we're both doing it the same way.

Measure the voltage on your black / white wire while you activate the switches. Do you see anything other than 0 volts at any time?
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Sunday, March 5th, 2017 AT 3:36 PM
Tiny
CHRIS EMERY
  • MEMBER
Just checking, did you get the picture I attached of the power seat plug showing the wire colors? Just want to make sure I'm working in the right spot.
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Sunday, March 5th, 2017 AT 4:07 PM
Tiny
CARADIODOC
  • EXPERT
I see eight wires in it, which is correct. Check where the wires go to. The wires must go to the three motors under the seat. There is another version that is for heated / climate-controlled seats. I don't know how many wires are in that plug.
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Sunday, March 5th, 2017 AT 4:28 PM
Tiny
CHRIS EMERY
  • MEMBER
Ok, Here is the results,

with - line grounded on frame and using the + tip to check current at each wire.
With each switch activated individually.(8 positions)

Purple - Hot

Tan - Seat forward 12+
Lt Grn - Seat back 12+

Grn/Wht - Seat back Recline 12+
Gray/Blk - Seat back forward 12+

Yellow - Seat bottom back up 12+
Lt Blue - Seat bottom back down 12+

Dk Blue - Seat bottom front down 12+
Dk Green - Seat bottom front up 12+

I also noticed that when activating a switch and "holding" that position, not only did that corresponding
wire show 12+, but all other positions showed 10.7 volts at the same time. Apparently, no ground at the switch?
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Tuesday, March 7th, 2017 AT 6:47 AM
Tiny
CARADIODOC
  • EXPERT
Yup. Without going back to the diagram, if you have 12 volts on multiple wires when a switch is activated, you're missing the ground. As I recall, the ground wire is bolted to the "B" pillar next to the driver's seat. I suspect you'll have to pop off a plastic trim cover and / or pull up the carpet.

A better way to verify this, without even having to worry about wire colors, is to measure the voltage across the two wires right at a motor's connector. If you're finding 10.7 volts on the ground wire, you're going to find the remainder of the 12 volts across the motor. That will be less than two and a half volts, which is not enough to make a motor run.
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Tuesday, March 7th, 2017 AT 9:49 AM
Tiny
CHRIS EMERY
  • MEMBER
Pulled the trim. Inspected the grounds. Traced the black wire in the harness (under the sill plate) to where it turns to go under the seat. Checked the ground to that point. Shows a good ground when probing the wire.
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Tuesday, March 7th, 2017 AT 10:22 AM
Tiny
CARADIODOC
  • EXPERT
Then there's only three possibilities. The terminal for the ground wire is stretched and not making good contact with the mating terminal. There's a break inside the switch assembly, most likely where the ground terminal is soldered to the circuit board, or all three switches are bad. That last one is not very likely.
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Tuesday, March 7th, 2017 AT 11:14 AM
Tiny
CHRIS EMERY
  • MEMBER
How do I isolate these down to one.

"There's a break inside the switch assembly, most likely where the ground terminal is soldered to the circuit board"
Are we talking about the power seat switch here? No ground present at the switch.

I agree I don't believe all three seat adjuster switches are bad (in 1 assembly).
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Tuesday, March 7th, 2017 AT 12:17 PM
Tiny
CARADIODOC
  • EXPERT
You should be able to pop the switch apart, then expect to find the switches soldered to some type of circuit board. Look at the terminal that corresponds to the black / white wire and see if it is loose where it is soldered or crimped to the board.

Even easier, find a switch at a salvage yard and plug it in to try it.
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Thursday, March 9th, 2017 AT 2:51 PM

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