P0C08: Drive Motor B Phase U-V-W Circuit/Open

P0C08 is the open-phase check for drive motor B, the motor B twin of P0C05. GM runs it on the 2011 Volt and the 2012 two-mode trucks: each phase is checked as the rotor passes its axis, and a phase axis current below 9 A while at least 23 A is commanded, with the rotor within 30 degrees and over 35 V on the inverter, counts as a miss. Around 200 failed samples set it, Type A, one trip. Later GM tables up to 2016 keep the same logic. GM's eAssist has only one machine and no P0C08. The usual causes are a loose three-phase terminal, an open stator winding or an inverter stage that does not conduct. Motor B then delivers no torque, the MIL lights and drive power is reduced.

Symptoms

• Malfunction indicator lamp after one drive
• Reduced propulsion power
• Engine running more often than usual

Most likely causes

• Loose or open three-phase terminal between inverter and motor B
• Open stator winding in drive motor B
• Inverter stage for motor B not conducting

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Check the continuity of the wire between the component and the control module.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

Good to know

• It can trigger limp mode.
• It affects emissions.

What each character of P0C08 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• C: Subsystem depends on the code range
• 08: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0C08?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0C08?

The most common causes are: loose or open three-phase terminal between inverter and motor B; open stator winding in drive motor B; inverter stage for motor B not conducting.

Related codes

• P0C09Drive Motor B Phase U-V-W Circuit Low
• P0C0ADrive Motor B Phase U-V-W Circuit High
• P0C05Drive Motor A Phase U-V-W Circuit/Open
• P0C04Drive Motor B Current High
• P0BFEDrive Motor B Phase U-V-W Current Sensor Correlation
• P0BF1Drive Motor B Phase U Current Sensor Circuit
• P0BF5Drive Motor B Phase V Current Sensor Circuit
• P0BF9Drive Motor B Phase W Current Sensor Circuit

Sources

• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• gsi.ext.gm.com: 12OBDG06 Hybrid Diagnostics
• gsi.ext.gm.com: 16OBDG01 Hybrid Diagnostics

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.