For 1990-2009 cars

### Diagnostic Aids

Noise from a generator may be due to electrical or mechanical noise. Electrical noise, 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 the engine.
3. Disconnect the 3 or 4-way connector from the generator.
4. Start the engine.
5. Listen for the noise.

Has the noise stopped?

Go to Step 11

Go to Step 3

3 |

1. Turn OFF the engine.
2. Remove the drive belt. Refer to Drive Belt Replacement in Engine Mechanical-8.1L or the CAT® Unit Repair Manual Engine Mechanical.
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 Drive Belt Replacement in Engine Mechanical-8.1L or the CAT® Unit Repair Manual Engine Mechanical.
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 in Engine Mechanical-8.1L or the CAT® Unit Repair Manual Engine Mechanical. 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 in Engine Mechanical-8.1L or the CAT® Unit Repair Manual Engine Mechanical.
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