why does my GMC Sierra T1XX (2019-Present) make a hissing noise when starting?

Discover the causes and solutions for hissing noise during engine start in GMC Sierra T1XX. Step-by-step diagnostic and repair guide included.

Solution

1. Preparation

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

2. Inspect and Repair the Intake System

• Tools Required: Socket set, screwdrivers, vacuum gauge
• Steps:
  1. Remove the engine cover if applicable.
  2. Inspect all intake hoses for cracks or loose clamps.
  3. Use a vacuum gauge to check for vacuum leaks; a reading lower than normal indicates a leak.
  4. Replace any damaged hoses or tighten loose clamps as necessary.

3. Check and Repair the Exhaust System

• Tools Required: Jack and jack stands, exhaust pipe wrench
• Steps:
  1. Raise the vehicle and securely support it with jack stands.
  2. Inspect the exhaust system, focusing on connections and the manifold for signs of leaks.
  3. If leaks are found, replace gaskets or sections of the exhaust as needed.
  4. Reassemble the exhaust system and lower the vehicle.

4. Testing and Final Checks

• Tools Required: OBD-II scanner
• Steps:
  1. Reconnect the battery.
  2. Start the engine and listen for the hissing noise.
  3. Use the OBD-II scanner to check for any new error codes.
  4. Confirm that the engine runs smoothly and that no additional noises are present.