WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
DTC C0398
Circuit
Short to Ground
Open/High Resistance
Short to Voltage
Actuator Plausibility Failure
Incremental Sensor - Rotational Position Sensor Correlation Plausibility