GMC Sierra T1XX (2019-Present) transmission slips when accelerating, what to do

GMC Sierra T1XX (2019-Present)

Error Codes

2-4 hours

Time

medium

Difficulty

high

Severity

3 min read

565 words

⚠️ Safety Warning

This issue requires immediate attention. If you are not experienced with automotive repairs, consult a professional mechanic. Working on critical systems can be dangerous.

Problem Statement

Learn how to diagnose and fix transmission slipping issues in GMC Sierra T1XX (2019-Present). Step-by-step guide with diagnostic procedures and repair instructions.

Affected Component

Transmission

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect battery before working on electrical systems.
•Allow engine to cool before opening the transmission pan.

Symptoms

•Transmission slips when accelerating
•Delayed engagement when shifting into drive or reverse
•Engine RPM increases without corresponding vehicle speed
•Check engine light may be illuminated
•Fluid leaks under the vehicle
•Burning smell from transmission fluid

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to check for transmission-related trouble codes.
2
Inspect the transmission fluid level and condition; check for contamination or burnt odor.
3
Examine the transmission fluid cooler lines for leaks or damage.
4
Test the transmission control module (TCM) for proper operation using a scan tool.
5
Perform a road test to replicate the slipping and note any specific conditions (e.g., cold starts, high speeds).
6
Check the condition of the transmission filter if accessible, and verify it's not clogged.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Socket set
•Torque wrench
•Drain pan
•Funnel
•Gasket scraper

Parts Required

•Transmission fluid (specific type as per manual)
•Transmission filter
•Gasket or sealant (if needed)
•Transmission Control Module (if replacement is necessary)

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Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to check for transmission-related trouble codes.
2
Inspect the transmission fluid level and condition; check for contamination or burnt odor.
3
Examine the transmission fluid cooler lines for leaks or damage.
4
Test the transmission control module (TCM) for proper operation using a scan tool.
5
Perform a road test to replicate the slipping and note any specific conditions (e.g., cold starts, high speeds).
6
Check the condition of the transmission filter if accessible, and verify it's not clogged.

Solution

1. Preparation

Gather required tools and parts.
Ensure the vehicle is parked on a level surface and the engine is turned off.
Disconnect the battery to prevent electrical issues.

2. Check and Replace Transmission Fluid

Drain Old Fluid
- Locate the transmission pan and place a drain pan underneath.
- Remove the drain plug or pan bolts and drain the old fluid completely.
- Tools: Socket set, drain pan.
Inspect Fluid Condition
- Check the fluid for metal shavings or burnt smell. If it appears contaminated, further inspection is required.
Replace Filter
- Remove the transmission pan completely and clean the mating surfaces.
- Replace the transmission filter according to manufacturer's specifications.
- Tools: Socket set, gasket scraper, new transmission filter.
Install New Gasket and Pan
- Apply a new gasket or sealant as needed and reattach the transmission pan.
- Torque bolts to the manufacturer's specifications.
- Tools: Torque wrench.
Refill Transmission Fluid
- Refill with the correct type and amount of transmission fluid as per the owner’s manual.
- Tools: Funnel.

3. Replace Transmission Control Module (if necessary)

Remove TCM
- Locate the TCM, typically found near the transmission or under the dashboard.
- Disconnect the electrical connectors and remove mounting bolts.
- Tools: Socket set.
Install New TCM
- Position the new TCM and secure it with bolts, then reconnect electrical connectors.
- Tools: Socket set.