P0B42 — Hybrid Battery Voltage Sense "B" Circuit Low

Meaning for brands

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P0B42 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the hybrid battery voltage sense "B" for damage, corrosion, chafing or poor contact.
Subsystem check Check for supply voltage at the hybrid battery voltage sense "B" connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P0B42 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0B42 (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P0B42 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How much does it cost to fix P0B42?

Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000; Replace the faulty sensor or actuator — $150–$500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will P0B42 clear itself?

Sometimes P0B42 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose P0B42 myself?

Start with a scan: confirm P0B42, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the hybrid battery voltage sense "B", and verify the suspect component against live data before buying parts.

Is it safe to drive with P0B42?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

What does OBD2 code P0B42 mean?

Hybrid Battery Voltage Sense "B" Circuit Low (P0B42): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector, blown fuse feeding the circuit.

When your scanner pulls code P0B42, the powertrain control module is telling you it detected a problem with the hybrid battery voltage sense "B" circuit reading abnormally low. Specifically, the voltage on this circuit has dropped close to ground potential, which means the module cannot get a valid signal from the sensing circuit. This falls under the powertrain category in the OBD2 standard, and it typically involves the hybrid battery monitoring system found in hybrid and plug-in hybrid vehicles.

The voltage sense circuit is responsible for feeding accurate battery pack voltage information back to the control module. When everything is working properly, this circuit carries a specific reference voltage. P0B42 sets when that voltage stays below the expected minimum threshold for a sustained period across multiple drive cycles. The most common culprits behind this are a direct short to ground somewhere in the wiring, insulation damage that exposes the signal wire to metal, a supply voltage that has been interrupted, or a faulty sensor that is dragging the signal down. The module constantly watches this circuit while you drive, and once it confirms the voltage has been out of range long enough to rule out a momentary glitch, it stores P0B42 and illuminates the check engine light. The freeze frame data captured alongside the code is invaluable — it shows you engine RPM, load, temperature, and vehicle speed exactly when the fault occurred.

The symptoms of P0B42 vary depending on how severely the voltage sense circuit is compromised. In most cases the check engine light will be the first sign. Depending on which specific sensor or system is affected by the low voltage reading, the vehicle may enter a reduced-power limp mode to protect drivetrain components. The system associated with the faulty sense circuit typically behaves erratically or stops functioning entirely. Some drivers also notice a spike in fuel consumption because the hybrid management system cannot properly balance battery charging and discharge without accurate voltage readings.

Common Symptoms of P0B42

Check Engine Light illuminated
Possible limp-home mode activation depending on the affected component
The related hybrid system operates intermittently or fails to operate at all
Increased fuel consumption in certain driving conditions

The root causes of P0B42 almost always trace back to electrical problems in the sense circuit. Wiring damage is the most frequent source — a chafed wire that shorts to ground will pull the signal voltage down immediately. A break or high-resistance connection in the supply voltage feed creates the same low-reading condition from the module perspective. The hybrid battery voltage sense "B" sensor itself can fail internally and drag the signal low. Beyond wiring and the sensor, a corroded or loose connector introduces resistance that mimics low voltage conditions. A blown fuse feeding that specific circuit will obviously cut supply voltage entirely. On the control module side, an internal driver fault or a poor ground connection at the module can also produce symptoms identical to a circuit-low condition.

What Causes P0B42

Signal wire shorted to ground from chafed or damaged insulation
Missing supply voltage reaching the hybrid battery voltage sense "B" circuit
Failed voltage sense "B" sensor internally dragging the signal low
Open circuit or secondary short somewhere in the wiring harness
Faulty sensor or actuator associated with the affected sense circuit
Corroded, loose, or otherwise damaged electrical connector
Blown fuse providing power to the circuit
Internal control module driver fault
Poor ground connection at the module or sensor

How to Diagnose P0B42

Connect your OBD2 scanner and verify P0B42 is present in the codes. Before clearing anything, record the freeze frame data — this snapshot of engine conditions when the fault triggered tells you exactly what load, RPM, temperature, and speed were present during the failure.
Scan for any other stored codes. Related diagnostic trouble codes often point toward the primary problem. Also search for technical service bulletins (TSB) specific to your make, model, and year — manufacturers frequently publish software updates or known fixes for persistent P0xxx codes. Check the manufacturer website or NHTSA database using your VIN.
Perform a thorough visual inspection of the wiring harness and connectors tied to the hybrid battery voltage sense "B" circuit. Look for worn insulation, exposed wire, corrosion buildup, and any connectors that are not fully seated or show signs of moisture intrusion.
At the sensor connector, check for proper supply voltage first. Then measure resistance from the signal wire to ground — a reading near zero ohms confirms a hard short to ground in the harness that needs to be located and repaired.
Back-probe the connector at the sensor itself and verify reference voltage, ground, and signal line continuity. Compare your readings to the specifications in your vehicle's repair manual.
With the harness connected and live data streaming on your scanner, perform a wiggle test on the wiring. Gently move the harness and connectors while watching the voltage reading — any dropouts or sudden fluctuations reveal intermittent opens or broken wire strands inside the insulation.
After repairs are made, clear the code and complete a full drive cycle that reproduces the conditions captured in the freeze frame. The code should not return.

Repair Options for P0B42

Always address the least expensive and most common failure points before considering component replacement. Wiring repairs and connector servicing typically resolve the issue. Control module repair or replacement is more involved and costs significantly more. Sensor or actuator replacement falls in the middle of the cost range.

Wiring harness repair or connector service: $80–$250
Control module diagnosis and repair: $300–$1,000
Hybrid battery voltage sense "B" sensor or actuator replacement: $150–$500

How Much Does It Cost to Fix P0B42?

The final bill depends entirely on what component is actually at fault. Here are typical all-in costs including parts and labor at an independent repair shop in the United States:

Wiring repair or connector replacement: $80–$250
Control module service: $300–$1,000
Sensor or actuator replacement: $150–$500

Across all possible repair scenarios, expect to spend between $80 and $1,000 to resolve P0B42. A solid diagnosis before purchasing parts is the single best way to keep costs down — the most expensive scenario is rarely the first one to blame, and replacing a perfectly good module will not fix a chafed wire.

Can You Drive with P0B42?

In most cases the vehicle remains driveable, though you may notice reduced performance or an auxiliary system (such as hybrid battery management) that does not function properly. The check engine light will stay on. If the vehicle exhibits stalling, failure to start, or warnings related to brakes or steering assist, treat the situation as urgent and have it towed rather than risking a breakdown in traffic.