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Code C0306, transfer case shift issues?

Tiny
WAYNE SHANNON
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 205,000 MILES
I have a 2003 1500 HD. I had a C0306 code but the service 4wd light only came on when driving in the rain. I was preparing to drive on the beach, and I shifted into neutral. Then shifted the transfer case from 2wd to 4wd high then as I shifted into 4wd low the selector switch lights went out, the service 4wd light came on and the 30-amp fuse blew. I tried to shift into gear, but I heard a loud grinding noise. The transfer case was in neutral. Next, I pushed it onto the street and flat towed it a half mile away. Next, I used a spare fuse to force the transfer case in 2wd and the fuse blew again.
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Saturday, July 1st, 2023 AT 12:49 PM

9 Replies

Tiny
MATHGEN
  • MECHANIC
  • 128 POSTS
Based on the code you have and the following symptoms, I suspect a failure in the shift motor for the transfer case. Let's rule out any wiring concerns first. I would start by testing for a short to ground at the 30A TRCC fuse socket, just make sure you are on the correct side of the socket. If your ohmmeter shows a short to ground, then unplug the shift motor connector at the transfer case and retest. If the short goes away, you know it's in the shift motor. If not, then unplug the transfer case control module. Then, if you still show a short to ground, there is a wiring issue you would need to track down.
I cut the schematic into 2 sections so it's easier to read. I hope this helps, please let me know if I can do anything else for you.
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Sunday, July 2nd, 2023 AT 11:26 AM
Tiny
WAYNE SHANNON
  • MEMBER
  • 5 POSTS
Thank you so much for the help. I didn’t get a chance to do anything with the repair until this weekend. My dad and I started testing the fuse and it turned out to TCCM was the issue. I went to advanced auto and purchased a rebuilt one, but they gave me a broken one and the truck got stuck in 4wd high. I went back and got another, and it seems to have fixed the issue. My scanner doesn’t have any codes right now, but I will wait a few days to see if I have any codes. I seriously appreciate the help and guidance.
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Sunday, July 9th, 2023 AT 5:17 PM
Tiny
MATHGEN
  • MECHANIC
  • 128 POSTS
You are very welcome. I am glad to hear that you got it repaired.
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Monday, July 10th, 2023 AT 4:42 AM
Tiny
WAYNE SHANNON
  • MEMBER
  • 5 POSTS
I’m not sure if it’s repaired but I believe the TCCM was faulty however I drove to work and the service 4wd light came on and I got the code C0306 motor A/B circuit malfunction. I’m going to do the same test again later, but I feel I may have to replace the shift motor as well. I tested it yesterday after replacing the TCCM and everything worked like it should.
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Monday, July 10th, 2023 AT 5:01 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Hi,

I noticed we haven't been in contact with you for a couple of days. Have you been able to make any progress? We're interested in knowing.

Take care,

Joe
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Wednesday, July 12th, 2023 AT 10:50 PM
Tiny
WAYNE SHANNON
  • MEMBER
  • 5 POSTS
I haven’t gotten the service 4wd light since, but I ran the same test again for everything including checking resistance in the wires related to the encoder motor. I checked while shaking the wiring harness and everything seemed okay. I’m going to clear the codes again to see if they come back. It’s also going to rain today so I will see if that makes the service 4wd light come on. I’m not sure where else to look or test if the light and code come back. If you have any other advice, please let me know.
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Thursday, July 13th, 2023 AT 6:44 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Hi,

Let us know if the light comes back on. There are a lot of codes from what I'm seeing. I'm interested in knowing, if it turns on, if all the codes return, or if it is limited.

Let us know.

Joe
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Thursday, July 13th, 2023 AT 11:48 AM
Tiny
WAYNE SHANNON
  • MEMBER
  • 5 POSTS
Light didn’t come on, but codes did. I drove home then put the scanner on it and drove it for 8 minutes after clearing the codes then used the 4wd went into every mode then checked codes again and nothing. I’m putting the videos in chronological order. It did not rain so I couldn’t determine if the service 4wd light would come on again. I do not have a lot of confidence in using the 4wd because I drive on the beach every weekend and I would like it to be reliable. If I cannot determine the issue, do you think it be wise to buy a manual transfer case?
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Thursday, July 13th, 2023 AT 4:20 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,645 POSTS
Hi,

If the codes returned, the light should have turned on. Are they the same codes? I'm starting to wonder if it is related to a module or controller.

Let me know.

Joe
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Thursday, July 13th, 2023 AT 7:08 PM

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