my GMC Sierra transmission slips when accelerating what's wrong

Learn how to diagnose and fix transmission slipping issues in GMC Sierra. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather tools and materials: OBD-II scanner, socket set, transmission fluid, funnel, cleaning rags, and safety gear.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Check and Replace Transmission Fluid

• Check Fluid Level:

  • Remove the transmission dipstick and wipe it clean.
  • Reinsert it and remove again to check the fluid level.
  • If low, add the correct type of transmission fluid as specified in the owner’s manual.

• Replace Fluid if Contaminated:

  • Drain the existing fluid by removing the drain plug or pan.
  • Replace the transmission filter if applicable.
  • Reinstall the pan and torque the bolts to manufacturer specifications.
  • Refill with new transmission fluid using the funnel.

3. Inspect and Repair Transmission Components

• Inspect Seals and Gaskets:

  • Visually inspect all seals and gaskets around the transmission for wear or damage.
  • Replace any faulty seals or gaskets to prevent leakage.

• Test and Repair Transmission Control Module:

  • Disconnect the battery to avoid electrical shorts.
  • Remove the transmission control module for inspection.
  • Check wiring for corrosion or breaks; repair or replace as necessary.

4. Road Test

• After completing repairs, take the vehicle for a test drive under varied conditions to ensure the slipping issue is resolved.
• Monitor performance and listen for any unusual sounds.