P0B56: Hybrid/EV Battery Voltage Sense F Circuit Low

The GM two-mode hybrids of 2012, Tahoe, Yukon, Escalade, Silverado and Sierra, show a detail of P0B56 that lithium-ion packs lack. Their nickel-metal hydride pack is read in blocks, channel F being block 6, and the battery pack control module sets the code only when block 6 and block 7 both read under 2 V in 15 of 20 samples at 100 ms, Type B, two trips; a shared sense wire between the blocks is the obvious suspect then. In GM's lithium-ion systems the battery energy control module uses 0.2 V or less on cell voltage F for 1.4 s within 2 s, Type A. In both cases the controller assumes a failed measurement and reduces battery use until repair.

Symptoms

• Hybrid system warning, MIL after the second drive (two-mode)
• Engine runs continuously, no electric launch
• Lower fuel economy

Most likely causes

• Fault in the sense wire shared by blocks 6 and 7 (GM two-mode)
• Channel F sense line shorted to a neighbouring line
• Failed input on the cell monitoring electronics

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. With the connector unplugged, check whether the signal wire is making contact with ground.
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 P0B56 means

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

Frequently asked questions

Can I keep driving with code P0B56?

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 P0B56?

The most common causes are: fault in the sense wire shared by blocks 6 and 7 (GM two-mode); channel F sense line shorted to a neighbouring line; failed input on the cell monitoring electronics.

Related codes

• P0B54Hybrid/EV Battery Voltage Sense F Circuit
• P0B55Hybrid/EV Battery Voltage Sense F Circuit Range/Performance
• P0B57Hybrid/EV Battery Voltage Sense F Circuit High
• P0B58Hybrid/EV Battery Voltage Sense F Circuit Intermittent/Erratic
• P0B51Hybrid/EV Battery Voltage Sense E Circuit Low
• P0B5BHybrid/EV Battery Voltage Sense G Circuit Low

Sources

• gsi.ext.gm.com: 12OBDG06 Hybrid Diagnostics
• gsi.ext.gm.com: 19OBDG01 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.