P0B99: Hybrid/EV Battery Voltage Sense S Circuit Intermittent/Erratic

P0B99 is the erratic variant within the sense S group. A public manufacturer description does not exist. GM's tables cover channel S from the 2011 Volt via the 2012 two-mode trucks and eAssist to the 2019 controllers, yet only with circuit, range, low and high codes (P0B95 to P0B98). CARB 1968.2 obliges manufacturers to monitor battery voltage sensors of a hybrid storage system for circuit and rationality faults and to separate the fault codes by replaceable unit, which is why J2012 reserves this slot. Should a vehicle set it, the technician would look for a sense S connection that works most of the time but breaks briefly, typically a fretting terminal or a cracked solder joint on the board.

Symptoms

• Sporadic hybrid warning without a pattern
• Code often stored as history, hard to reproduce

Most likely causes

• Fretting corrosion on the terminal of sense lead S
• Cracked solder joint for channel S on the monitoring board
• Harness chafing that only shorts under movement

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. Gently move the wiring with the engine running and watch whether the reading changes.
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 P0B99 means

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

Frequently asked questions

Can I keep driving with code P0B99?

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 P0B99?

The most common causes are: fretting corrosion on the terminal of sense lead S; cracked solder joint for channel S on the monitoring board; harness chafing that only shorts under movement.

Related codes

• P0B95Hybrid/EV Battery Voltage Sense S Circuit
• P0B96Hybrid/EV Battery Voltage Sense S Circuit Range/Performance
• P0B97Hybrid/EV Battery Voltage Sense S Circuit Low
• P0B98Hybrid/EV Battery Voltage Sense S Circuit High
• P0B94Hybrid/EV Battery Voltage Sense R Circuit Intermittent/Erratic
• P0B9EHybrid/EV Battery Voltage Sense T Circuit Intermittent/Erratic

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 13OBDG05C Hybrid Diagnostics
• gsi.ext.gm.com: 11OBDG01 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.