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Diagnostic Aids

Noise from a generator may be due to electrical or mechanical noise. Electrical noise or magnetic whine usually varies with the electrical load placed on the generator and is a normal operating characteristic of all generators. When diagnosing a noisy generator, it is important to remember that loose or misaligned components around the generator may transmit the noise into the passenger compartment and that replacing the generator may not solve the problem.

Step

Action

Yes

No

1

Test the generator for proper operation using the Generator Tester. Refer to Charging System Test .

Is the generator operating properly?

Go to Step 2

Go to Step 11

2
  1. Start the engine. Verify that the noise can be heard.
  2. Turn OFF all accessories.
  3. Turn OFF the ignition.

    4. Caution: Make sure that the load is completely turned off before connecting or disconnecting a carbon pile load tester to the battery. Otherwise, sparking could ignite battery gasses which are extremely flammable and may explode violently.

  4. Connect a carbon pile tester to the vehicle.
  5. Connect an inductive ammeter probe to the output circuit of the generator.
  6. Start the engine.
  7. Increase engine speed to 1,500 RPM.
  8. Increase and decrease the amount of load placed upon the generator.
  9. Listen for the noise.

Does the noise increase and decrease with the amount of load placed upon the generator by the carbon pile tester?

Go to Step 11

Go to Step 3

3
  1. Shut OFF the engine.
  2. Remove the drive belt. Refer to Generator Drive Belt Replacement or Drive Belt Tensioner Replacement - Generator.
  3. Spin the generator pulley by hand.

Does the generator shaft spin smoothly and without any roughness or grinding noise?

Go to Step 4

Go to Step 11

4

Inspect the generator for a loose pulley and/or pulley nut.

Is the generator pulley or pulley nut loose?

Go to Step 11

Go to Step 5

5
  1. Loosen all of the generator mounting bolts.
  2. Tighten the generator mounting bolts to specifications and in the proper sequence, if necessary. Refer to Generator Replacement.
  3. Install the drive belt. Refer to Generator Drive Belt Replacement or Drive Belt Tensioner Replacement - Generator.
  4. Start the engine.

Has the noise decreased or stopped?

System OK

Go to Step 6

6

Inspect the generator for the following conditions:

    • Strained or stretched electrical connections
    • Hoses or other vehicle equipment resting on the generator, which may cause the noise to be transmitted into the passenger compartment

Are any electrical connections pulling on the generator or are any hoses, etc. resting on the generator?

Go to Step 7

Go to Step 8

7
  1. Reroute the electrical connections to relieve the tension.
  2. Reroute the hoses, etc. away from the generator.
  3. Start the engine.

Has the noise decreased or stopped?

System OK

Go to Step 8

8

Inspect the drive belt for proper tension. Refer to Drive Belt Tensioner Diagnosis or Drive Belt Tensioner Replacement - Generator.

Is the drive belt loose?

Go to Step 9

Go to Step 10

9
  1. Replace the drive belt tensioner. Refer to Drive Belt Tensioner Replacement - Generator.
  2. Start the engine.

Has the noise decreased or stopped?

System OK

Go to Step 11

10

Compare the vehicle with a known good vehicle.

Do both vehicles make the same noise?

System OK

Go to Step 11

11

Important: If no definite generator problems were found, be sure that all other possible sources of objectionable noise are eliminated before replacing the generator. Replacing the generator may not change the noise level if the noise is a normal characteristic of the generator or the generator mounting.

Replace the generator. Refer to Generator Replacement.

Has the noise decreased or stopped?

Go to Step 12

--

12

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2