P0B73
Hybrid/EV Battery Voltage Sense L Circuit Range/Performance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- B
- AreaHybrid propulsion
- 73
- FaultThe specific fault in that area
What it means
P0B73 means the hybrid or EV battery control unit has found that the signal from one of its battery voltage sense circuits (labelled 'L') is out of range or does not agree with other voltage measurements. The control unit compares this reading with the other sense circuits, the total pack voltage and its expected values, and sets the code when they do not make sense together. Which cell group or sensor 'L' refers to depends on the vehicle and battery design.
Symptoms
- Hybrid, EV or battery system warning light on the dashboard
- Malfunction indicator lamp on
- Reduced power or the car going into a limp-home mode
- Reduced or erratic electric-only range or battery state-of-charge reading
- Hybrid system not starting or the car not going into ready mode
- Poor fuel economy because the hybrid system is limiting battery use
Possible causes
- Loose, corroded or damaged connector or terminal on the battery voltage sense wiringlikely
- Damaged, chafed or open-circuit sense wiring or harnesslikely
- Fault in the battery monitoring or battery control module's voltage sensingpossible
- Weak or imbalanced cell or module in the high-voltage battery giving a genuine out-of-range voltagepossible
- Poor connection at a high-voltage busbar or service disconnect, causing a voltage droppossible
- Moisture or coolant ingress in the battery pack affecting the sense circuitsrare
- Outdated control unit software where the manufacturer has issued a known update for this faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting any other battery voltage, temperature or isolation codes that appear alongside P0B73.
- Check for manufacturer service bulletins and software updates relevant to the model and the high-voltage battery.
- Only if you are trained and qualified for high-voltage work, make the system safe following the manufacturer's procedure before touching any high-voltage components.
- Visually inspect the battery pack's sense wiring, connectors and harness routing for damage, corrosion, moisture, chafing or loose pins.
- Using live data, compare the individual cell or module voltages and the total pack voltage, and look for one reading that is out of line with the rest.
- Check the voltage sense circuit for continuity, short circuits and resistance against the manufacturer's wiring diagram and specifications.
- Check the battery pack's busbars and connections for looseness, heat damage or high resistance, following the manufacturer's procedure.
- If wiring and connections are sound, test the battery monitoring module and the pack's balance and capacity as the manufacturer specifies before condemning any part.
How to fix
- Clean, repair or replace faulty connectors and terminals on the voltage sense circuit.
- Repair or replace damaged sense wiring or the harness section.
- Rebalance or repair the high-voltage battery, or replace the weak cell, module or pack if testing confirms it is faulty.
- Replace the battery monitoring or control module if it is confirmed to be reading incorrectly.
- Tighten or repair high-voltage busbar connections, and dry out and repair any moisture ingress, following the manufacturer's procedure.
- Apply a manufacturer-issued software update if one exists for this fault, then clear the code and confirm it does not return.
Can I keep driving?
The car may be driveable, often with reduced power, but the fault could be a sign of a developing battery problem, so get it checked soon. Stop driving and seek help if the car warns of a high-voltage fault, loses drive, or you notice a smell, heat or fluid leaking from the battery area.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.