P0B66: Hybrid/EV Battery Voltage Sense I Circuit High

When channel I claims a voltage above what its cell or block can physically reach, the controller stores P0B66. The thresholds GM publishes depend on chemistry and architecture: lithium-ion packs with a battery energy control module set it at 4.8 V or more for 1.4 s in a 2 s window, Type A, one trip; the BAS Plus mild hybrid at above 4.65 V in 7 of 10 samples, Type B; the 2012 two-mode trucks, which measure nickel-metal hydride block 9 rather than single cells, above 23 V in 15 of 20 samples, Type B. Every limit sits clearly above normal full charge, so a real overcharged cell is unlikely. Look first for a sense lead touching the next tap up or for a measuring input that has lost its reference.

Symptoms

• Charging stops or is refused
• MIL and reduced power

Most likely causes

• Channel I lead touching a higher-potential tap
• Open reference or ground of the measuring chip
• Genuinely overcharged cell after a charging control fault

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 sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P0B66 means

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

Frequently asked questions

Can I keep driving with code P0B66?

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 P0B66?

The most common causes are: channel I lead touching a higher-potential tap; open reference or ground of the measuring chip; genuinely overcharged cell after a charging control fault.

Related codes

• P0B63Hybrid/EV Battery Voltage Sense I Circuit
• P0B64Hybrid/EV Battery Voltage Sense I Circuit Range/Performance
• P0B65Hybrid/EV Battery Voltage Sense I Circuit Low
• P0B67Hybrid/EV Battery Voltage Sense I Circuit Intermittent/Erratic
• P0B61Hybrid/EV Battery Voltage Sense H Circuit High
• P0B6BHybrid/EV Battery Voltage Sense J Circuit High

Sources

• gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
• gsi.ext.gm.com: 13OBDG05C Hybrid Diagnostics
• gsi.ext.gm.com: 12OBDG06 Hybrid Diagnostics
• law.cornell.edu: 13 CCR 1968.2

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.