why does my GMC Sierra T1XX (2019-Present) transmission slip when shifting?

Learn how to diagnose and fix transmission slipping issues in GMC Sierra T1XX (2019-Present). 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 cool.
• Disconnect the battery to avoid electrical shocks.

2. Check and Replace Transmission Fluid

• Sub-step 1: Remove the transmission dipstick and check the fluid level.
• Sub-step 2: If low, add the manufacturer-recommended transmission fluid until the correct level is reached.
• Sub-step 3: If fluid is dark or burnt, drain the old fluid using a fluid pump or by removing the transmission pan.
• Sub-step 4: Replace with fresh transmission fluid of the specified type.

3. Replace Transmission Filter and Gasket

• Sub-step 1: Remove the transmission pan bolts with a socket set.
• Sub-step 2: Carefully lower the pan and remove the old filter.
• Sub-step 3: Install the new filter and replace the pan gasket.
• Sub-step 4: Reattach the transmission pan and tighten bolts to manufacturer torque specifications.

4. Inspect and Repair Electrical Connections

• Sub-step 1: Check all TCM connectors and wiring for damaged insulation or corrosion.
• Sub-step 2: Clean any corroded connections with electrical cleaner.
• Sub-step 3: Secure any loose connections and ensure proper seating.

5. Test Drive and Adjust

• Sub-step 1: Reconnect the battery and start the vehicle.
• Sub-step 2: Take the vehicle for a test drive to assess shifting performance.
• Sub-step 3: If issues persist, consider reprogramming or replacing the TCM.