What Does P0B42 Mean?
The battery management system has detected a low voltage condition on the hybrid battery voltage sense "B" circuit. The reading is below the minimum threshold, indicating either a genuine low cell group voltage, a short to ground in the sense wiring, or a failed BMS input.
Safety Warning
Do not drive until diagnosed. Low voltage readings require verification to rule out cell failure and potential thermal events.
Common Causes
30%
Short to ground in the voltage sense B wiring
30%
Genuine low cell group voltage from degraded cells
25%
Corroded sense wire connection causing voltage drop
15%
BMS sense input channel fault reading low
Diagnostic Steps
1
Step 1: Measure actual cell group voltage with HV-rated DVOM. Normal voltage means the sense circuit is faulty, not the cells.
2
Step 2: If voltage is genuinely low, check individual cells to identify the failed cell.
3
Step 3: Disconnect sense B at the BMS and check for shorts to ground on the sense wires.
4
Step 4: Inspect cell tab connections for corrosion or loose joints.
5
Step 5: If wiring is intact and cells are healthy, test by swapping BMS sense inputs between channels.
Estimated Repair Cost
$150 - $3,000
Parts + labor, varies by vehicle and location
The battery management system has detected a low voltage condition on the hybrid battery voltage sense "B" circuit. The reading is below the minimum threshold, indicating either a genuine low cell group voltage, a short to ground in the sense wiring, or a failed BMS input.
The most common cause of P0B42 (Hybrid Battery Voltage Sense "B" Circuit Low) is: Short to ground in the voltage sense B wiring
Typical repair costs for P0B42 range from $150 to $3,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Do not drive until diagnosed. Low voltage readings require verification to rule out cell failure and potential thermal events.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B42 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid Battery / High Voltage System
Difficulty
Type
Generic (SAE)
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