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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Mechanical - 4.6L (LH2) 🢒 Drive Belt Rumbling Diagnosis

Diagnostic Aids

Vibration from the engine operating may cause a body component or another part of the vehicle to make rumbling noise.

The drive belt may have a condition that can not be seen or felt. Sometimes replacing the drive belt may be the only repair for the symptom.

If replacing the drive belt, completing the diagnostic table, and the noise is only heard when the drive belts are installed, there might be an accessory drive component with a failure. Varying the load on the different accessory drive components may aid in identifying which component is causing the rumbling noise.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This test is to verify that the symptom is present during diagnosing. Other vehicle components may cause a similar symptom.

    2.

  2. This test is to verify that one of the drive belts is causing the rumbling noise. Rumbling noise may be confused with an internal engine noise due to the similarity in the description. Remove only one drive belt at a time if the vehicle has multiple drive belts. When removing the drive belts the water pump may not be operating and the engine may overheat. Also DTCs may set when the engine is operating with the drive belts removed.

    3.

  3. Inspecting the drive belts is to ensure that they are not causing the noise. Small cracks across the ribs of the drive belt will not cause the noise. Belt separation is identified by the plys of the belt separating and may be seen at the edge of the belt our felt as a lump in the belt.

    4.

  4. Small amounts of pilling is normal condition and acceptable. When the pilling is severe the drive belt does not have a smooth surface for proper operation.

Step

Action

Yes

No

Notice: Refer to Belt Dressing Notice in the Preface section.

DEFINITION:

    • A low pitch tapping, knocking, or thumping noise heard at or just above idle.
    • Heard once per revolution of the drive belt or a pulley.
    • Rumbling may be caused from:
       - Pilling, the accumulation of rubber dust that forms small balls (pills) or strings in the drive belt pulley groove
       - The separation of the drive belt
       - A damaged drive belt

1

Did you review the Drive Belt Symptom operation and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Engine Mechanical

2

Verify that there is a rumbling noise.

Does the engine make the rumbling noise?

Go to Step 3

Go to Diagnostic Aids

3

  1. Remove one of the drive belts. Refer to Generator Drive Belt Replacement or Water Pump and Air Conditioning Compressor and Power Steering Pump Belt Replacement .
  2. Operate the engine for no longer than 30-40 seconds.
  3. Repeat this step if necessary by removing the remaining belt.

Does the rumbling noise still exist?

Go to Symptoms - Engine Mechanical

Go to Step 4

4

Inspect the drive belts for damage, separation, or sections of missing ribs.

Did you find any of these conditions?

Go to Step 7

Go to Step 5

5

Inspect for severe pilling of more than 1/3 of the drive belt pulley grooves.

Did you find severe pilling?

Go to Step 6

Go to Step 7

6
  1. Clean the drive belt pulleys using a suitable wire brush.
  2. Reinstall the drive belts. Refer to Generator Drive Belt Replacement or Water Pump and Air Conditioning Compressor and Power Steering Pump Belt Replacement .

Did you complete the repair?

Go to Step 8

Go to Step 7

7

Install a new drive belt. Refer to Generator Drive Belt Replacement or Water Pump and Air Conditioning Compressor and Power Steering Pump Belt Replacement .

Did you complete the replacement?

Go to Step 8

--

8

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Diagnostic Aids