What Does P0B77 Mean?
DTC P0B77 indicates a general malfunction in the hybrid battery voltage sense circuit for cell group "M." The BMS has detected an unspecified fault when reading voltage from this cell group. As a general circuit code, it indicates the BMS knows there is a problem but the fault does not fall neatly into a high, low, or range/performance classification, requiring manual diagnosis to isolate the root cause.
Common Causes
30%
Open circuit in the cell group M voltage sense wiring
25%
Corroded or damaged connector at the cell group M voltage tap
20%
Failed BMS voltage sensing input for the M channel
15%
Failed or severely degraded battery cell within group M
10%
Multiple simultaneous faults preventing specific classification
Diagnostic Steps
1
Check for companion DTCs on cell groups L and N, and review freeze frame data for voltage, temperature, and operating conditions at fault time.
2
Access the hybrid battery enclosure and inspect cell group M voltage sense connector for physical damage, corrosion, or moisture.
3
Perform continuity and insulation resistance checks on the sense wiring between the BMS module and cell group M.
4
Measure cell group M voltage directly at the battery terminals and compare to expected values based on state of charge.
5
Verify ground path integrity for the BMS sensing circuit and battery pack assembly.
6
If wiring and cells check good, perform manufacturer-specific BMS module diagnostics to evaluate the sensing channel health.
Estimated Repair Cost
$200 - $2,800
Parts + labor, varies by vehicle and location
DTC P0B77 indicates a general malfunction in the hybrid battery voltage sense circuit for cell group "M." The BMS has detected an unspecified fault when reading voltage from this cell group. As a general circuit code, it indicates the BMS knows there is a problem but the fault does not fall neatly i...
The most common cause of P0B77 (Hybrid Battery Voltage Sense "M" Circuit) is: Open circuit in the cell group M voltage sense wiring
Typical repair costs for P0B77 range from $200 to $2,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of voltage monitoring for cell group M prevents the BMS from maintaining proper charge balance and thermal oversight. The vehicle will likely reduce or disable hybrid functionality. Extended operation risks undetected cell degradation or imbalance in the affected group.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B77 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Battery System
Difficulty
Type
Generic (SAE)
Recommended Tools
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