P0B4A: Hybrid/EV Battery Voltage Sense D Circuit

P0B4A is the open-circuit code of cell sense channel D, the fourth measuring channel of the battery monitoring electronics. GM checks it in the battery energy control module with the same open sense line logic as the other channels: a gap of 1.3 V or more between adjacent cells, under 36 mV on a cell being balanced, or splice voltages above 0.1 V or 0.5 V at a bus bar, for 0.6 s, Type A. For diagnosis, the pattern matters: if P0B4A stands alone, inspect the channel D tap and its connector; if Ford's whole open-line group from P0B3B upwards is set, as on the 2019-2020 Fusion PHEV or the 2023 Mach-E and E-Transit, a common cause such as the BECM flex cable or the battery itself is more likely.

Symptoms

• No start or vehicle will not go into ready mode
• Charging not possible
• Several sense channel codes stored together

Most likely causes

• Open channel D sense tap or connector (code set alone)
• Faulty BECM flexible printed circuit affecting several channels (Ford Mach-E, E-Transit)
• Internal traction battery fault (Ford Fusion PHEV)

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. Make sure the battery cooling air intake is clean
3. Check the 12 V auxiliary battery, which can also trigger warnings
4. 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 P0B4A means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• B: Subsystem depends on the code range
• 4A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0B4A?

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 P0B4A?

The most common causes are: open channel D sense tap or connector (code set alone); faulty BECM flexible printed circuit affecting several channels (Ford Mach-E, E-Transit); internal traction battery fault (Ford Fusion PHEV).

Related codes

• P0B4BHybrid/EV Battery Voltage Sense D Circuit Range/Performance
• P0B4CHybrid/EV Battery Voltage Sense D Circuit Low
• P0B4DHybrid/EV Battery Voltage Sense D Circuit High
• P0B4EHybrid/EV Battery Voltage Sense D Circuit Intermittent/Erratic
• P0B45Hybrid/EV Battery Voltage Sense C Circuit
• P0B4FHybrid/EV Battery Voltage Sense E Circuit

Sources

• gsi.ext.gm.com: 19OBDG01 Hybrid Diagnostics
• static.nhtsa.gov: MC 10232489 0001
• static.nhtsa.gov: MC 11005840 0001
• 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.