P0B78

Code

Generic P — Powertrain

Hybrid/EV Battery Voltage Sense M Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 31 EN: 31 RU: 35

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in the battery voltage sense M wiring or connector
Poor or corroded connector or pin at the battery pack or module
Faulty voltage divider or sensing resistor in battery pack
Intermittent connection (broken wire, chafing, poor terminal)
Battery pack control module (BCM/VCM) or vehicle control module fault
Incorrect calibration, software or configuration issue

Symptoms

DTC P0B78 set and related hybrid/EV system warning lamp(s) illuminated
Reduced hybrid/EV system performance or limp-home mode
Battery state-of-charge (SOC) or pack voltage readouts erratic or out of range on scan tool
Charging or regeneration disabled
Possible unexpected system behavior or drivability restrictions

What to check

Read and record freeze frame and all related hybrid/EV codes and data using a capable scan tool
Verify technician and workshop comply with high-voltage safety procedures before any physical inspection
Check for accompanying codes from the battery pack control module or high-voltage system
Visually inspect battery pack connectors, harness routing, and chassis ground points for damage, corrosion or moisture
Check connector mating condition and pin security at the battery pack and main control module
Use a scan tool to monitor measured pack voltage and the voltage reported by the sense M circuit in real time

Signal parameters

Battery voltage sense line: typically a scaled 0–5.0 V signal to the vehicle control module (actual scale depends on vehicle pack/divider)
Open-circuit: near 0 V (or floating) if open; short-to-battery: near pack-divider voltage; short-to-ground: ~0 V
Expected behavior: sense voltage correlates proportionally with actual pack voltage and remains stable under normal load change
Continuity: low ohms between sense pin and module (no high resistance or intermittent)

Diagnostic algorithm

Confirm DTC and note freeze-frame data with an advanced scan tool and clear codes to see if fault returns
Follow manufacturer high-voltage safety/isolation procedures before touching the HV system — only qualified technicians should perform HV work
Visually inspect harness, connector seals, and pin condition at the battery pack and control module; repair any physical damage
Backprobe the sense M signal with the ignition in the correct state and compare the measured voltage to the pack voltage (expect a proportional, stable 0–5 V signal per vehicle divider ratio)
Check continuity and resistance of the sense circuit between the battery pack and the vehicle control module; look for shorts to ground or battery
Wiggle-test the harness and connectors while monitoring the sense voltage for intermittent changes
Inspect and test the internal voltage divider/sensor inside the battery pack per manufacturer procedure; replace pack or divider component if confirmed faulty
Check for related module communication errors on CAN and verify the BCM/VCM is powered and communicating properly
If wiring and pack internals are good, check for software calibrations/updates and reflash modules if instructed by manufacturer TSBs
After repairs, clear codes and perform a road or charge/discharge cycle to verify the circuit remains within expected range and the code does not return

Likely causes

Damaged or disconnected sense harness at battery pack
Corroded or bent pins in the sense connector
Failed resistor/divider or sensor inside the battery pack assembly
Faulty pack control module sending invalid sense values
Intermittent short to ground or to pack voltage on the sense line

Fault status

⚠️ Status

Hybrid/EV battery voltage sense M circuit reporting out-of-range voltage or performance; circuit reading does not match expected battery pack voltage behavior.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.5 - 4.0 hours