Rotor Test

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

Using an ohmmeter, measure resistance between slip rings. Perform STEP 1 in figure. See Fig 1 . If resistance is not 2.7-3.1 ohms, replace rotor.
Using an ohmmeter, measure resistance between rotor and slip rings. Perform STEP 2 in figure. See Fig 1 . If resistance is less than 5 ohms, replace rotor.
Inspect slip rings. If slip rings are scored, rough or diameter is less than .504" (12.8 mm), replace rotor.

Fig 1: Testing Generator Rotor

Courtesy of GENERAL MOTORS CORP.