P0B4C

What it means

P0B4C means the hybrid or EV control unit has seen the signal from the 'D' battery voltage sense circuit reading lower than the expected range. The unit compares this signal with its other voltage measurements and its plausible limits. The 'D' sensing point (a cell block, module group or sense channel) depends on the vehicle, so check the manufacturer data for which one it is.

Symptoms

• Hybrid or EV system warning light on, often with the main warning light
• Reduced power or limp mode
• Car will not go into READY mode or will not start
• Poor or inconsistent state-of-charge readings on the display
• Engine running more often than normal on a hybrid, with poorer economy
• Hybrid battery charging or assist limited

Possible causes

• Damaged, corroded or loose connector or terminal in the battery voltage sense circuitlikely
• Open circuit or short to earth in the voltage sense wiring or harnesslikely
• Fault in the battery monitoring unit or its internal sense channelpossible
• Real low voltage in the cell block or module being monitored, from a weak or failing battery modulepossible
• Moisture or coolant ingress, or contamination at the battery pack connectorspossible
• Fault in the hybrid control unit or an outdated calibration, where the manufacturer has issued a bulletin for itrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, and note whether other battery voltage, cell balance or insulation codes are present.
2. Check for manufacturer service bulletins and software updates for this code on the model and engine in question.
3. Look at the live data for each battery block or module voltage and compare it with the others, noting whether 'D' is lower than the rest or reads zero.
4. Visually inspect the accessible battery sense connectors, harness routing and the pack for damage, corrosion, moisture or chafing, following the high-voltage safety procedure.
5. Only if you are trained and qualified for high-voltage systems, isolate the system as the manufacturer specifies and test the sense circuit for continuity, short to earth and resistance.
6. Check the 12 volt battery condition and the supply and earth to the battery monitoring unit, as low supply can cause false readings.
7. Compare the measured module voltage with the sensed value to tell a wiring or sensor fault from a genuinely weak module.
8. Clear the code and road test, rechecking live data to see whether the fault returns.

How to fix

• Repair or replace damaged wiring, terminals or connectors in the voltage sense circuit.
• Clean or dry the connectors and remove the source of any moisture or contamination.
• Replace or repair the battery monitoring unit if its sense channel is faulty.
• Repair or replace the weak battery module or pack where the low voltage is genuine, following the manufacturer's procedure.
• Fix any 12 volt supply or earth fault to the monitoring unit.
• Apply a manufacturer calibration update only where an outdated calibration is a known cause for this code.

Can I keep driving?

Nearby codes

• P0B4BGenericHybrid/EV Battery Voltage Sense D Circuit Range/Performance
• P0B4DGenericHybrid/EV Battery Voltage Sense D Circuit High