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 symptoms, diagnostic steps, and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is off.
• Disconnect the battery to prevent electrical shorts.

2. Check and Replace Transmission Fluid

• Sub-steps:
  1. Remove the transmission dipstick and wipe it clean.
  2. Insert the dipstick back, remove it again, and check the fluid level.
  3. If low, add the appropriate type of transmission fluid (consult the owner’s manual).
  4. If fluid is dirty or burnt, proceed to drain and replace.
• Tools Required: Transmission fluid pump, funnel, fluid container.

3. Inspect and Replace Transmission Filter

• Sub-steps:
  1. Raise the vehicle using jack stands and remove the transmission pan.
  2. Remove the old filter and replace it with a new one.
  3. Clean the transmission pan and reinstall it with a new gasket.
• Tools Required: Socket set, gasket scraper, torque wrench, new transmission filter, pan gasket.

4. Perform Transmission Pressure Test

• Sub-steps:
  1. Connect a transmission pressure gauge to the appropriate port.
  2. Start the engine and monitor the pressure while shifting through gears.
  3. If pressures are out of specification, consider replacing the transmission pump or solenoids.
• Tools Required: Transmission pressure gauge, appropriate adapters.

5. Electrical Inspection

• Sub-steps:
  1. Inspect wiring harnesses and connectors for wear or damage.
  2. Use a multimeter to test the throttle position sensor and vehicle speed sensor.
  3. Replace any faulty sensors or connectors as necessary.
• Tools Required: Multimeter, wiring repair tools.