Update Chevy HPCM Before Replacing Transmission
This bulletin applies to 2014 Chevy Spark EV vehicles. The technician may report an intermittent whine, howl, hum or buzz noise or vibration during regenerative braking or when backing up. P0618 may be set current or in history.
According to Chevy, do not replace the transmission for this concern, or if the ATF is dark in color. Check to see if the Hybrid Powertrain Control Module (HPCM) T6 software can be updated (drive motor generator power inverter module reprogramming) using the Service Programming System (SPS) via Techline Information System (TIS1Web).