why is my GMC Sierra T1XX (2019-Present) check engine light on with code P0700

Learn how to diagnose and fix P0700 transmission control malfunction in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

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

2. Check Transmission Fluid

• Remove the transmission dipstick and check fluid level.
• If low, add manufacturer-recommended transmission fluid.
• If dirty or burnt, perform a fluid change (see step 4).

3. Inspect Wiring and Connectors

• Visually inspect the wiring harness leading to the TCM for frays or corrosion.
• Clean any corroded connectors using electrical contact cleaner.
• Ensure all connections are securely fastened.

4. Replace Transmission Fluid (if necessary)

• Tools Required: Socket set, fluid pump, catch pan.
• Sub-steps:
  1. Remove the transmission pan bolts and carefully lower the pan.
  2. Clean the pan and replace the filter if applicable.
  3. Reinstall the pan with new gasket material, torque bolts to manufacturer specifications (typically 12-15 ft-lbs).
  4. Use a fluid pump to refill the transmission with the appropriate fluid through the dipstick tube.

5. Reprogram or Replace TCM (if necessary)

• If the TCM is faulty:
  1. Remove any fasteners securing the TCM in place and disconnect the wiring harness.
  2. Install the new or reprogrammed TCM by reversing the removal process.
  3. Ensure all connections are secure and reattach any protective covers.

6. Reconnect Battery

• Reconnect the battery terminals and ensure they are tight.