07 Yukon C0306 Service 4wd (most fixes tried already)

[Tray0625]

C0306 (Motor A/B Circuit) persists for over a year and all the parts and $ thrown at it. Please Help!

I have done;
- actuator
- selector switch
- TCCM
- TCCM wire harness
- Encoder Motor & relearn flash
- Checked all external grounds, cleaned
- checked all fuses
- I do not see broken wires anywhere

I have had it at the dealership twice since I got to a dead end on what to do next. They cleaned grounds, and have not found it either. I can't keep paying through the nose for them to look either.

****clue*** Both times from dealer, once they cleared the codes with their GM scanner, the 4WD light goes off for a couple of days. In that couple of days, the 4WD WILL work correctly!! It shifts into 4hi, 4lo, N, & 2wd and functions correctly. Then C0306 comes back on.

When I clear the code with my BlueDriver, it does not work.

My next tries (if I don't set this thing on fire and walk away);

- try a different encoder motor (maybe I got a defective one?)
- clean terminals on all harnesses (pretty much already been done)
- try to find wire harness diagram and check every inch of it (please send if you have one)
- maybe replace encoder motor wire harness?


At this point I am almost considering bypassing the OEM wire harness and rewiring the entire system myself.

What would your next move be? What do you suggest?
First time posting, but have followed the forum trying to fix this. Much appreciated.

 

[j91z28d1]

I don't have any ideas about the issue, but I think you're a prime case to buy a clone tech 2. and then go from there.

 

[Geotrash]

C0306 (Motor A/B Circuit) persists for over a year and all the parts and $ thrown at it. Please Help!

I have done;
- actuator
- selector switch
- TCCM
- TCCM wire harness
- Encoder Motor & relearn flash
- Checked all external grounds, cleaned
- checked all fuses
- I do not see broken wires anywhere

I have had it at the dealership twice since I got to a dead end on what to do next. They cleaned grounds, and have not found it either. I can't keep paying through the nose for them to look either.

****clue*** Both times from dealer, once they cleared the codes with their GM scanner, the 4WD light goes off for a couple of days. In that couple of days, the 4WD WILL work correctly!! It shifts into 4hi, 4lo, N, & 2wd and functions correctly. Then C0306 comes back on.

When I clear the code with my BlueDriver, it does not work.

My next tries (if I don't set this thing on fire and walk away);

- try a different encoder motor (maybe I got a defective one?)
- clean terminals on all harnesses (pretty much already been done)
- try to find wire harness diagram and check every inch of it (please send if you have one)
- maybe replace encoder motor wire harness?


At this point I am almost considering bypassing the OEM wire harness and rewiring the entire system myself.

What would your next move me? What do you suggest?
First time posting, but have followed the forum trying to fix this. Much appreciated.

I have had a couple of situations on these trucks where disconnecting wiring to replace a part resulted in intermittent error messages over the following weeks after the repair. In both cases, taking apart the connectors and hitting them with electronics or electrical contact cleaner before putting them back together again, solved the issue. The first time was on the autoride shock connectors on my '07 a few years ago. The second time it was the left front wheel speed sensor that I replaced a few weeks ago on my '07. Kept getting an ABS lights and chime every time I drove it until I cleaned the wiring connector on Monday. No more problems since. Might be worth a "shot".

 

[j91z28d1]

if you really wanna deep dive into what the dealership tech probably doesn't feel like doing. this is the tree I found. I guessed it's not the all time awd t case since you said you have a 2wd option

 

[Tray0625]

I have had a couple of situations on these trucks where disconnecting wiring to replace a part resulted in intermittent error messages over the following weeks after the repair. In both cases, taking apart the connectors and hitting them with electronics or electrical contact cleaner before putting them back together again, solved the issue. The first time was on the autoride shock connectors on my '07 a few years ago. The second time it was the left front wheel speed sensor that I replaced a few weeks ago on my '07. Kept getting an ABS lights and chime every time I drove it until I cleaned the wiring connector on Monday. No more problems since. Might be worth a "shot".

I'll give that a shot, thanks!

 

[Tray0625]

if you really wanna deep dive into what the dealership tech probably doesn't feel like doing. this is the tree I found. I guessed it's not the all time awd t case since you said you have a 2wd option

Thanks, I will check it out. And yes, 4WD not AWD.

Much appreciated, all this info is from the tech 2 you referred to?

 

[j91z28d1]

that info is from a pay shop software . the tech 2 is the dealer level scanner. but instead of the $2k plus you can get them for about 300$.

 

[Tray0625]

Alright guys, I have a theory. Give me your feedback please.

Truck displays C0306-02 (Motor A-B Circuit short to ground)

Couldn't I just run my own new external ground, rather than trying to find where it is shorted?

If so, any suggestions on best spot to run a new ground?

I will be thoroughly cleaning all connectors and meter testing them over the weekend. But I am really curious if I can solve it by just running my own ground.

Let me know your thoughts, I will update on if I find anything this weekend.

Thanks!

 

[Fless]

According to the code, the circuit is already shorted to ground. Running another ground wouldn't cure that.

 

[Tray0625]

Guess it's time to get the test light out. Anyone have wiring diagrams for this system?

 

[89Suburban]

Guess it's time to get the test light out. Anyone have wiring diagrams for this system?

Look at D-11. Hopefully this helps.

2007_LD_ElectricalPickupsChassisCabs.pdf

drive.google.com

 

[Tray0625]

I will check it out, just need a full day i can dig into it. Much appreciated. I have skimmed this diagram a few times in the past. Having trouble making sense of what wires are which pins in connectors, and how it translates to what I'm looking at. Will do more studying.

I was trying to install a new stereo this weekend and found more "clues"

Under the driver's dash panel there are 4 cut wires dangling (previous owner). One of them is light blue 18ga is the only one that has power running to it. Others do not. These are directly next to the TCCM that I replaced. Since i moved (just moved, not unplugged) the TCCM to try and follow these mystery wires I have a new "transfer case control module" light on.

I'm suspicious. Perhaps pins are loose in TCCM harnesses? Or a wire is poorly spliced?

I'm assuming previous owner had an aftermarket alarm, breathalyzer, or GPS tracker in the truck and did a poor job of removing it.

Also, when opening driver's door, the dome lights do not come on as they do for all the other doors. Door functions fine otherwise. Been like that since I bought it, just assumed it had a bad door latch. Maybe that's where the light blue wire is supposed to go?

I'm now wondering if they cut a wire to the 4wd, or reconnected something incorrectly.

Oh, and the stereo gave static feedback constantly. So I pulled it back out. Not sure if that problem is connected to the others I just listed.

So. FML.

What's the little blue wire go to? What about the others? Why the new TC light?

Is there a place to get wire assignments/pin connectors?

What would your next move be? Lost cause?

 

[Tray0625]

I will check it out, just need a full day i can dig into it. Much appreciated. I have skimmed this diagram a few times in the past. Having trouble making sense of what wires are which pins in connectors, and how it translates to what I'm looking at. Will do more studying.

I was trying to install a new stereo this weekend and found more "clues"

Under the driver's dash panel there are 4 cut wires dangling (previous owner). One of them is light blue 18ga is the only one that has power running to it. Others do not. These are directly next to the TCCM that I replaced. Since i moved (just moved, not unplugged) the TCCM to try and follow these mystery wires I have a new "transfer case control module" light on.

I'm suspicious. Perhaps pins are loose in TCCM harnesses? Or a wire is poorly spliced?

I'm assuming previous owner had an aftermarket alarm, breathalyzer, or GPS tracker in the truck and did a poor job of removing it.

Also, when opening driver's door, the dome lights do not come on as they do for all the other doors. Door functions fine otherwise. Been like that since I bought it, just assumed it had a bad door latch. Maybe that's where the light blue wire is supposed to go?

I'm now wondering if they cut a wire to the 4wd, or reconnected something incorrectly.

Oh, and the stereo gave static feedback constantly. So I pulled it back out. Not sure if that problem is connected to the others I just listed.

So. FML.

What's the little blue wire go to? What about the others? Why the new TC light?

Is there a place to get wire assignments/pin connectors?

What would your next move be? Lost cause?

UPDATE;

Some problems solved, and some new clues...

* I'm thinking the light blue wire is driver's door light, will test and confirm

* Feedback from new stereo is most likely due to the Kenwood HU over powering Bose amp, so I will bypass the Bose amp for the door speakers only. That should fix that issue.

* AS FOR the 4WD (which is what this post was about in the first place) We've had a crazy cold winter and I have not had time to get back at it yet. We got a bunch of snow, and I found a new clue; The 4WD works perfectly fine AS LONG AS THE "SERVICE 4WD" light is not lit. When the service light comes on, it will not shift and is stuck in whatever setting. Usually when you first start the truck after its been sitting a while, you have a minute or two before the "Service 4WD" light comes on, and you can select what ever setting you want. During longer drives the "Service 4WD" light will cycle on and off a few times. So it's intermittent.

I am assuming a wire issue, OR a lose pin in a connector somewhere. Intermittent may make it difficult to test with a signal scanner, but that's what I plan to do next.

I pulled and cleaned connectors on TCCM, encoder, and actuator. I was conscious of plugging them in deliberately & solid. I also pulled and cleaned the other smaller connectors near the encoder motor, and I did notice that one of those connectors coming from the main harness is taught with zero slack to plug into its sensor. I am not sure what sensor it is. But it did concern me that it was so tight. I am suspicious if that's my culprit. Need to find out if those wires are just pwr/gnd and can be extended, or if they're info wires I suppose.

I did have an issue with the drivers window not rolling up, and found the wires that go into the connector liked to be folded a certain way. When folded to the left, no power. When folded to the right, works fine. So I'm thinking it's something silly like that.

Anyone have any other suggestions on how to find a finnicky gremlin like that, other than signal scanner?

Thanks!