2025 GMC Sierra 2500HD Serpentine Belt Routing, Length & Part Numbers

As an ASE-certified master technician, I know that keeping your 2025 GMC Sierra 2500HD on the road means staying on top of routine maintenance. The serpentine belt is the lifeline for your engine's accessories, driving the alternator, water pump, power steering pump (or electric assist depending on configuration), and A/C compressor.

Note: The 2025 GMC Sierra 2500HD is offered with two powerhouse engines: the 6.6L L8T Gas V8 and the 6.6L L5P Duramax Turbo-Diesel. The specifications below are tailored specifically to the standard 6.6L Gas V8. The Duramax diesel features a different, dual-belt configuration.

Quick answer

Here are the vital specifications and part numbers you need for the 2025 GMC Sierra 2500HD (6.6L Gas V8):

• Rib Count: 6-rib
• Belt Length: 102.0 inches (approximate effective length)
• OEM Belt Part Number: GM Genuine 12698263
• Aftermarket Cross-References:
  • Gates: K061020
  • Dayco: 5061020
  • Continental Elite: 4061020
• OEM Auto-Tensioner Part Number: GM Genuine 12698264 (or ACDelco equivalent)
• OEM Idler Pulley Part Number: GM Genuine 12685785

Belt routing

Pro-tip: Always use your smartphone to take a few clear photographs of your existing belt before removing it. It will save you a massive headache if you get confused during reinstallation.

Since we don't have a diagram to show you, follow this text-based routing path for the 6.6L Gas V8. Picture the front of the engine block as a clock face:

1. Start by looping the ribbed side of the belt around the bottom of the Crankshaft Pulley (the largest pulley at the bottom center).
2. Route the belt up and to the right (passenger side) around the outside of the A/C Compressor.
3. Bring the flat side of the belt back inward over the smooth Idler Pulley.
4. Route the ribbed side up and around the Alternator at the top passenger side.
5. Bring the belt across the top of the engine to the driver's side and around the Power Steering / Accessory Pump.
6. Route the flat side of the belt down and under the smooth Water Pump pulley (center of the engine).
7. Finally, pull the belt around the Auto-Tensioner pulley (driver's side, below the water pump).

How to replace the serpentine belt

Replacing the serpentine belt on a 2025 Sierra 2500HD is straightforward if you have the right tools. You will need a serpentine belt tool or a standard long-handled 3/8" breaker bar.

1. Locate the tensioner: Find the automatic spring-loaded tensioner assembly on the lower driver's side of the engine front cover.
2. Release the tension: Insert your 3/8" drive breaker bar or serpentine belt tool into the square slot on the tensioner arm.
3. Remove the belt: Rotate the tensioner counter-clockwise (away from the belt) to relieve the spring tension. With the tension released, slip the old belt off the nearest smooth idler pulley. Let the tensioner return to its resting position gently.
4. Route the new belt: Follow the routing instructions above, saving the tensioner or idler pulley for last.
5. Install the new belt: Rotate the tensioner again using your breaker bar, slip the new belt onto the final pulley, and slowly release the tensioner.
6. Verify: Visually inspect every pulley to ensure the belt ribs are perfectly seated in the pulley grooves. Start the engine and observe the belt to ensure smooth operation.

Replacement interval

For heavy-duty trucks like the Sierra 2500HD, the serpentine belt should be thoroughly inspected every 30,000 miles. Standard replacement is generally recommended between 60,000 and 90,000 miles, or every 5 to 7 years, whichever comes first. If you frequently tow heavy loads, idle for extended periods, or drive in harsh, dusty environments, you may need to replace it closer to the 60,000-mile mark.

Signs of a failing belt or tensioner

Don't wait for a breakdown on the highway. Watch for these common warning signs:

• Squealing or Chirping Noises: A high-pitched squeal on startup or during acceleration usually points to a stretched belt or a weak tensioner spring.
• Visible Cracks or Missing Chunks: Modern EPDM belts don't crack as obviously as old neoprene belts, but any missing rib material or heavy chunking means immediate replacement.
• Fraying Edges: If the edge of the belt is fuzzy or fraying, it indicates a pulley misalignment or a failing tensioner bearing.
• Accessory Issues: A loss of power steering assist, random A/C dropouts, or a battery warning light can indicate a slipping belt.
• Tensioner Bounce: With the engine running, watch the tensioner arm. A tiny bit of vibration is normal, but excessive bouncing means the internal damping spring is shot and the tensioner assembly needs replacing.

If you aren't comfortable doing this job in your driveway, don't worry. Find a trusted shop on Repairius.