GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Mechanical - 6.6L (LB7) 🢒 Drive Belt Squeal Diagnosis

Diagnostic Aids

A loose or improper installation of a body or suspension component, or other item(s) on the vehicle may cause the squeal noise.

If the squeal is intermittent, verify that it is not the accessory drive component(s) by varying their load(s), making sure they are operating to their maximum capacity. An overcharged air conditioning (A/C) system, a power steering system restriction or the incorrect fluid, or a failing generator are suggested items to inspect.

Test Description

The number(s) below refer to the step(s) in the diagnostic table.

  1. The squeal may not be engine related. This step is to verify that the engine is making the noise. If the engine is not making the noise, do not proceed further with this table

    2.

  2. The squeal may be an internal engine noise. Remove the drive belt and operate the engine for a few seconds, this will verify if the squealing noise is related to the drive belt or an accessory drive component. With the drive belt removed the cooling fan will not be operate and the engine may overheat. Also diagnostic trouble codes (DTCs) may set when the engine is operated with the drive belt removed.

    3.

  3. This test is to verify that an accessory drive component(s) does not have a seized bearing. With the belt removed, test the bearings in the accessory drive component(s) for smooth operation. Also test the accessory drive components with the engine operating by varying the load on the accessory drive component(s) to verify that the component(s) is operating properly.

    4.

  4. This test is to verify that the drive belt tensioner is operating properly. If the drive belt tensioner is not operating properly, proper belt tension may not be achieved to keep the drive belt from slipping which could cause a squealing noise.

    5.

  5. This test is to verify that the drive belt is not too long, which would prevent the drive belt tensioner from operating properly. Also if the incorrect length drive belt was installed, it may not be routed correctly and may be turning an accessory drive component in the incorrect direction.

    6.

  6. Misalignment of the accessory drive pulley(s) may be caused from improper mounting or incorrect installation of a accessory drive component, or the pulley may be bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found, refer to that accessory drive component for the proper removal and installation procedure for that pulley.

    7.

  7. Inspect the accessory drive pulley(s) to verify that they are the correct diameter or width. Using a known good vehicle, compare the accessory drive pulley(s).

Step

Action

Yes

No

Notice: Do not use belt dressing on the drive belt. Belt dressing causes the breakdown of the composition of the drive belt. Failure to follow this recommendation will damage the drive belt.

DEFINITION: The following items are indications of drive belt squeal:

    • A loud screeching noise that is caused by a slipping drive belt (this is unusual for a drive belt with multiple ribs)
    • The squeal occurs when a heavy load is applied to the drive belt, such as an A/C compressor engagement, snapping the throttle, slipping on a seized pulley or a faulty accessory drive component.

1

Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Engine Mechanical

2

Verify that there is a squealing noise.

Does the engine make the squeal noise?

Go to Step 3

Go to Diagnostic Aids

3

  1. Remove the drive belt. Refer to Drive Belt Replacement .
  2. Operate the engine for no longer than 30 to 40 seconds.

Does the squealing noise still exist?

Go to Engine Noise on Start-Up, but Only Lasting a Few Seconds

Go to Step 4

4

Inspect for a seized accessory drive component bearing or a faulty accessory drive component.

Did you find and correct the condition?

Go to Step 9

Go to Step 5

5

Inspect the drive belt tensioner for proper operation. Refer to Drive Belt Tensioner Diagnosis .

Did you find and correct the condition?

Go to Step 9

Go to Step 6

6

Check for the correct length drive belt

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

Inspect for a misaligned pulley.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

8

Inspect for an in correct size pulley.

Did you find and correct the condition?

Go to Step 9

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9
  1. Install the drive belt. Refer to Drive Belt Replacement .
  2. Clear any codes.
  3. Run the engine in order to verify the repair.

Does the squealing noise still exist?

--

System OK