Transmission Issue on 2011 Silverado: Not Shifting to 2nd Gear in Drive Mode

dean33

Original poster
Member
Jul 6, 2024
5
USA
I'm currently dealing with a transmission issue on a 2011 Silverado. Here's the problem: the truck refuses to shift to 2nd gear when in Drive mode (Auto). However, when I switch to manual mode and drive for a bit, then switch back to Drive mode, the transmission operates normally.

Here are the details:
- Transmission fluid level is optimal and the filter is in good condition.
- There are no ECM or TCM trouble codes indicating transmission issues.
- However, I am receiving TCCM codes C0306, C0392, C0321, and C0396.This only affects 4WD operation isnt it?

I've already checked the basics like fluid levels and filters, and everything seems fine in that regard. Has anyone experienced a similar issue or have any suggestions on how to further diagnose and fix this problem?

Thanks in advance.
 

azswiss

Member
May 23, 2021
949
Tempe, AZ
Judging from the codes it sounds like this may be an electrical issue. Start by checking the grounds and electrical connectors to the transmission and transfer case. Do they use road salt where you live?

The link below has some great diagnostic info:
https://charm.li/Chevy Truck/2011/Silverado 1500 4WD V8-5.3L/Repair and Diagnosis/A L L Diagnostic Trouble Codes ( DTC )/#Testing and Inspection/

Click on the "C Code Charts" and then drill down to the specific code for detailed diagnostic procedures. Note, you will need to specify which transfer case you have.
 

Mooseman

Moderator
Dec 4, 2011
25,663
Ottawa, ON
Was anything done to the transfer case or tranny? Is the speedometer working? If not, the connectors for the two speed sensors might have been switched.
 

dean33

Original poster
Member
Jul 6, 2024
5
USA
Was anything done to the transfer case or tranny? Is the speedometer working? If not, the connectors for the two speed sensors might have been switched.
Yes,The transfer case was replaced.
Speedometer is working fine.
 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,663
Ottawa, ON
Still, check the two speed sensors, maybe try to swap them. It could also be related to the transfer case if it's an electrical issue, like @azswiss mentioned.
 

dean33

Original poster
Member
Jul 6, 2024
5
USA
Still, check the two speed sensors, maybe try to swap them. It could also be related to the transfer case if it's an electrical issue, like @azswiss mentioned.
Could you please tell which two speed sensors.Are you mentioning the input and output speed sensors bolted on to the valve body?
 

dean33

Original poster
Member
Jul 6, 2024
5
USA
I removed the valve body from the transmission and took a photo of the clutch gaps underneath. I noticed there's enough space to fit a 3mm diameter screwdriver inside. Is this amount of gap normal for the clutch assembly?
VideoCapture_20240707-211415.jpg
Screenshot_20240707-212244_Gallery.jpg
 

Mooseman

Moderator
Dec 4, 2011
25,663
Ottawa, ON
Could you please tell which two speed sensors.Are you mentioning the input and output speed sensors bolted on to the valve body?


There is one for the front transfer case output shaft and another for the rear unless they changed that on later years, had that issue on a truck with a 4L60 that wouldn't shift because the two were swapped.
 

dean33

Original poster
Member
Jul 6, 2024
5
USA
I removed the valve body and TCM, checked the pressure switches and solenoid with an external 12V supply (the solenoid latching was a bit feeble,i dont know if that is normal), and reinstalled everything.

Initially after reinstalling, the transmission exhibited the same shifting issue where it wouldn't shift to 2nd gear properly under acceleration. After clearing all engine, transmission, and transfer case codes with an OBD scanner, the problem persisted during my first test drive. However, after clearing the codes a couple more times, the issue seems to have resolved itself, and the car now shifts properly.

The concern now is that although the car is running fine, diagnostic trouble codes (DTCs) have started appearing without any noticeable issues. Initially, there were no codes when the shifting problem occurred.

Could anyone provide insight into why clearing the codes multiple times seems to have fixed the shifting issue temporarily? What could be causing the new codes to appear now, even though the transmission is operating normally? Any advice on what steps to take next would be greatly appreciated.

In short:Before there were shifting issues,but no DTC's.Now,There are no shifting issues,but DTC's appeared.

The codes are
P0700,P2771,P0967,P0971,P2721,P2730
 

Mooseman

Moderator
Dec 4, 2011
25,663
Ottawa, ON
Was the TEHCM replaced or reprogrammed in any way? It may need to be programmed to the PCM or relearned which requires a Tech 2 or another advanced scan tool. If not, sounds like it may have developed a problem and may need to be replaced or rebuilt. The pillows in the pressure switches can fail, which all the tranny codes point to pressure problems.
 

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