What Does P0B79 Mean?
DTC P0B79 indicates that the hybrid battery voltage sense circuit for cell group "M" is reading below the minimum expected voltage threshold. The BMS consistently detects a lower-than-expected voltage signal from this cell group. This low condition points to either physically weak cells producing insufficient voltage or a circuit issue that reduces the measured signal below the true cell voltage.
Common Causes
30%
Degraded or failing cells in group M with reduced open-circuit voltage
25%
High-resistance connection in the sense circuit causing voltage drop
20%
Short to ground in the cell group M sense wiring
15%
Elevated self-discharge rate in group M cells due to internal degradation
10%
BMS sensing channel input fault reading below actual voltage
Diagnostic Steps
1
Record freeze frame data showing cell group M voltage compared to pack average. Note how much below threshold the reading falls.
2
Measure cell group M voltage directly at the battery terminals. Compare this measurement to the BMS reported value.
3
If direct measurement confirms low voltage, perform a cell capacity test to identify weak or failing cells within the group.
4
If the direct measurement is higher than BMS reading, trace the sense circuit for voltage drops across connectors and wiring.
5
Check for ground shorts by measuring insulation resistance of the sense wiring to chassis ground.
6
If individual cells are confirmed weak, consult manufacturer procedures for cell module replacement eligibility and safety precautions.
Estimated Repair Cost
$200 - $3,500
Parts + labor, varies by vehicle and location
DTC P0B79 indicates that the hybrid battery voltage sense circuit for cell group "M" is reading below the minimum expected voltage threshold. The BMS consistently detects a lower-than-expected voltage signal from this cell group. This low condition points to either physically weak cells producing in...
The most common cause of P0B79 (Hybrid Battery Voltage Sense "M" Circuit Low) is: Degraded or failing cells in group M with reduced open-circuit voltage
Typical repair costs for P0B79 range from $200 to $3,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Persistently low cell voltage risks deep discharge damage, which is irreversible in most lithium battery chemistries. Deep discharge can cause internal shorts and cell swelling. The BMS should be protecting the cells by limiting discharge, which may manifest as reduced power availability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0B79 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Battery System
Difficulty
Type
Generic (SAE)
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