P0BA9 opens the W group, the twenty-third cell voltage channel, and flags a sense lead that is open or badly connected. GM's 2019 battery energy control module checks seven cases, ranging from a reading under 36 mV while the balancing gate of that cell is switched on to at least 1.3 V between neighbouring cells and splice voltages above 0.1 V or 0.5 V at busbar joints; 0.8 s of failure within 1.6 s sets it as Type A. The 2016 Volt module uses a 0.6 s window instead. GM's eAssist mild hybrid needs readings under 1.4 V on lines N and N-1 plus a change of more than 0.5 V within 200 ms in seven of ten samples, Type B. With the lead lost, the cell behind it can neither be balanced nor protected.
High severity. Can I keep driving?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.
Symptoms
- MIL with hybrid or EV system warning
- Reduced propulsion power or no ready mode
- Charging interrupted or refused
Most likely causes
- Broken, chafed or unplugged sense lead W
- High-resistance busbar or splice joint at channel W
- Failed input on the cell monitoring board for W
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- It can trigger limp mode.
- It affects emissions.
What each character of P0BA9 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- B: Subsystem depends on the code range
- A9: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0BA9?
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 P0BA9?
The most common causes are: broken, chafed or unplugged sense lead W; high-resistance busbar or splice joint at channel W; failed input on the cell monitoring board for W.
Related codes
- P0BAAHybrid/EV Battery Voltage Sense W Circuit Range/Performance
- P0BABHybrid/EV Battery Voltage Sense W Circuit Low
- P0BACHybrid/EV Battery Voltage Sense W Circuit High
- P0BADHybrid/EV Battery Voltage Sense W Circuit Intermittent/Erratic
- P0BA4Hybrid/EV Battery Voltage Sense V Circuit
- P0BAEHybrid/EV Battery Voltage Sense X Circuit
Sources
- gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
- gsi.ext.gm.com: 16OBDG01 Hybrid Diagnostics
- gsi.ext.gm.com: 13OBDG05C 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.