P0B90

What it means

P0B90 is the generic code for a fault in the Hybrid/EV battery voltage sense 'R' circuit. The battery control unit compared the signal from that voltage sensing circuit with what it expected and found it out of range, erratic or missing. Which cell, module or sense channel 'R' refers to depends on the vehicle, so check the manufacturer's data for the model.

Symptoms

• Hybrid or EV system warning light on the dashboard
• Reduced power or limp mode
• Reduced electric assist or reduced EV range
• Car will not go to READY or will not charge
• Poor fuel economy as the hybrid system limits battery use
• Other hybrid battery codes stored alongside it

Possible causes

• Damaged, corroded or loose connector or wiring in the battery voltage sensing harnesslikely
• Fault in the battery monitoring unit or battery control module's voltage sense channelpossible
• Real voltage imbalance or a weak cell or module in the high voltage battery packpossible
• Poor connection at the battery pack's internal sensing leads or bus barspossible
• Low or failing 12 V auxiliary battery causing unreliable readings in the control unitpossible
• Water ingress or coolant or condensation contamination in the battery pack or its electronicsrare
• Outdated control unit software where a manufacturer bulletin lists it as a known causerare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, such as battery state of charge, temperature and pack voltage, plus any related hybrid battery codes.
2. Test the 12 V auxiliary battery and its charging, as low supply voltage can cause false sensing faults.
3. Check the manufacturer's information for what sense circuit 'R' means on this model and where its wiring and connectors are.
4. Using live data, compare the individual cell or block voltages with the total pack voltage and look for one reading that is missing, stuck or out of line with the rest.
5. Only if trained in high voltage work: isolate the high voltage system as per the manufacturer's procedure and verify it is dead before touching any orange cabling or the pack.
6. With the system isolated, inspect the sensing harness and connectors for damage, corrosion, moisture, chafing or pushed-out pins, and check the pack for water or contamination.
7. Test the sense circuit for continuity, short circuits and resistance against the manufacturer's specification.
8. Check for software updates or technical bulletins for this model and code before replacing any control unit.

How to fix

• Repair or replace damaged wiring, terminals or connectors in the voltage sense harness.
• Clean and secure the pack's sensing connections and bus bar connections, and fix any moisture ingress.
• Replace the faulty voltage sensing or battery monitoring module as per the manufacturer's procedure.
• Service or replace the affected battery module or pack if the voltage imbalance is real, following the manufacturer's instructions.
• Replace the 12 V auxiliary battery if it is weak or failing.
• Update the control unit software only where a manufacturer bulletin names it as a cause.

Can I keep driving?

Nearby codes

• P0B8FGenericHybrid/EV Battery Voltage Sense Q Circuit Intermittent/Erratic
• P0B91GenericHybrid/EV Battery Voltage Sense R Circuit Range/Performance