Automatic GMC Transmission Issues in Highland, IL

Auto Repair
GMC Tranmission

We will list many GMC transmission problems here, their typical causes, and some advice on how to fix GMC transmission difficulties on your own in Highland, IL.

Common Symptoms

  • Cannot move shifter in and out of park
  • The vehicle won’t move when put in drive
  • The vehicle won’t change gears; stuck in fail-safe mode (limp mode)
  • Check engine light is visible
  • Rough shifting
  • Transmission slips
  • Cannot move the shifter to any gear


  • Brake light Switch: If you are having problems moving your shifter in and out of park, you might have a faulty brake light switch. Having a faulty shifter or bad ignition can also cause this issue.
  • Vehicle Speed Sensor: The speed sensor of your vehicle can cause erratic shifting and can cause your transmission to get stuck in one gear, putting your car in limp mode, which in turn causes the check engine light to turn on.
  • Low Transmission Fluid: Easily one of the most common transmission issues. Occurs when you don’t have enough transmission fluid.
  • Overheating: When transmission fluid overheats, it can cause harsh shifting and failures of GMC transmissions. This is a common problem for GMC trucks used for hauling or towing heavy loads.
  • Shifter Link: The shifter link is what connects the shifter to the transmission valve body. When this is misaligned, it can cause stop the vehicle from moving when it is put in drive.
  • Value Body: When a GMC vehicle has a faulty valve body, it can cause many issues. You might notice that shifting becomes harsher or is delayed.

GMC Transmission Problems

  • Delayed Shifting: GMC vehicles can develop issues with gear shifting. You will notice this problem when the gear changes take too long to occur. Along with this, you may notice that the transmission may not downshift during accelerations. These symptoms of these issues can happen only from time to time or they can be constant. These issues can be caused by clogged or inconsistent shift solenoids, a faulty throttle position sensor, or even a worn-down torque converter clutch.
  • Being Unable to Reverse: GMC vehicles can have issues when trying to select reverse. You may find that you cannot engage reverse gear despite your other gears working as they should. This can be caused by malfunctioning servos engaging the reverse gear. It won’t be able to create the oil pressure needed to engage the gear when it starts leaking. You can easily replace it but it involves removing the valve body and oil pan.
  • Stuck in First Gear or Higher Gears Missing: GMC Vehicles can have issues switching to higher gears. You may not be able to switch from second gear to third gear or be completely stuck in first gear. The problem could be with the clutch which can wear down. This can be replaced by replacing the clutch pack and engagement piston. The issue could also come from having a broken or worn-down drive shell collar or splines, which can cause the transmission to be locked into first gear. The only option you have is to replace the drive shell.
  • Shaking During Gear Changes: During a gear shift, you may notice your GMC vehicle shutter and have harsh shifting. You may even hear a clunking sound. This issue can be present in any gear change but is most noticeable in the second and first gears. One cause for this issue is using the wrong transmission fluid type. You can fix this problem in a GMC vehicle that uses an 8-speed transmission by replacing the fluid with Mobil 1 Synthetic LV ATF HP fluid. If the problem is still there you may need to replace your torque converter.
  • Gear Shift Slipping, Overheating, and Incorrect Shifting: These issues can arise in newer GMC trucks. These issues are usually caused by having a worn pressure regulator system. This system is what ensures the correct hydraulic pressure needed for the operation of the transmission. Pressure drops when this system’s components wear out which is what causes the shifting issues. You will need to either replace or rebuild the system to fix the problem.
  • Transmission Temperature: The transmission temperature can become a problem in your GMC vehicle, causing harsh shifting among other issues. You will need to see if there is an issue with the transmission fluid temperature system and check your transmission fluid levels.
Transmission Repair


  • Checking Transmission Fluid Levels: To check your transmission fluid levels, park your car on level ground, pop the hood open and secure it, locate the dipstick for your transmission, remove and clean it, then reinsert it and remove it to see the measurement.
  • Reading Fault Codes: Park your vehicle and turn it off, find the diagnostic port underneath the dashboard, plug in your scanner, allow it to communicate with your GMC model, select the control units then the transmission, and read the fault codes.

If you need help with figuring out what’s wrong with the transmission on your GMC vehicle, give our team of experts over at Marshall’s Transmission a call today and we can assist you in any way we can.