Hybrid/EV Powertrain Control Module Performance Fault

Common Symptoms

• Sudden loss of propulsion while driving, dash shows 'Service High Voltage Charging System' or 'Propulsion Power Is Reduced' message
• Vehicle enters reduced power mode or cuts drive torque entirely with no warning, then may recover after you cycle the ignition OFF and back to RUN or READY
• P1B03 stored alongside P0A3F in freeze-frame data when you pull codes with a scan tool
• Yellow or red propulsion warning light illuminates on the instrument cluster
• Vehicle may roll to a stop and refuse to move until restarted, but starts normally afterward making the fault seem intermittent
• No abnormal sounds, smells, or charging faults, the fault feels purely electrical and unpredictable
• Fault returns within a short drive cycle, especially over rough pavement or after temperature cycling

Probable Causes (Ranked by Likelihood)

• Spread or backed-out terminal in transmission harness connector X2, allowing intermittent signal dropout to the HPCM2, the confirmed root cause per GM TSB 19-NA-220 Very Likely
• Corroded or water-intruded pins at connector X2 causing high resistance on the HPCM2 communication circuit Likely
• Chafed or pinched transmission harness wiring between the drive unit and the HPCM2, creating intermittent opens under vibration Likely
• Failed or intermittent HPCM2 internal logic causing false performance fault detection without an external wiring cause Possible
• CAN bus integrity issue on the powertrain network segment causing HPCM2 to lose communication with adjacent modules and log a performance fault Possible
• Software fault in HPCM2 that predates a calibration update, logging P1B03 without a true hardware fault present Less Likely

Step-by-Step Diagnostic Procedure

1. Start by connecting GDS2, Autel MaxiSys, or Foxwell NT530 with GM software to the OBD port. A generic OBD-II reader will not display P1B03 or P0A3F. Confirm both codes are stored and capture the freeze-frame data, noting vehicle speed, battery state-of-charge, and coolant temperature at the moment of fault.

2. Check whether P0A3F is stored alongside P1B03. Per GM TSB 19-NA-220, this pairing points directly at the spread terminal in transmission harness connector X2. If both codes appear together, go to connector X2 before doing anything else.

3. Locate transmission harness connector X2 on the drive unit. On the Bolt EV, this is a multi-pin gray or black connector on the front-facing side of the drive unit assembly under the hood. With the ignition in OFF, unplug the connector and visually inspect every pin for spread, pushed-back, or deformed terminals. Use a dental pick or terminal probe to gently tug each wire to verify it seats firmly. A spread terminal will pull back slightly or feel loose.

4. Inspect the connector body and pins for corrosion, green oxidation, or water residue. Even light surface corrosion on a low-voltage signal pin creates enough resistance to cause HPCM2 performance faults. Clean with electrical contact cleaner and a pin cleaning tool if contamination is found.

5. Trace the transmission harness from connector X2 back toward the HPCM2, looking for chafe points against brackets, the firewall, or the drive unit casting. Pay attention to any section that moves with drivetrain torque or suspension travel. Flex the harness by hand while a second person watches live data on the scan tool for signal dropouts.

6. If no wiring fault is found, use GDS2 to check for any available HPCM2 calibration or software updates. GM released updated HPCM2 calibrations as part of the TSB 19-NA-220 fix package. A dealer-level GDS2 subscription is required to perform module programming. This step requires a tech with programming access.

7. After repairs, clear all DTCs and perform a minimum 10-mile drive cycle that includes highway speed, regenerative braking events, and at least one full stop-and-go sequence to confirm the fault does not reset. If P1B03 returns without P0A3F and no wiring fault is found, HPCM2 replacement may be necessary, which is an advanced dealer procedure.

8. If the connector X2 spread terminal is confirmed and corrected, verify the repair holds by road testing over rough pavement specifically, since vibration is the most common trigger for the intermittent contact loss that sets this code.

Frequently Asked Questions