What it means
The control module detects an intermittent or erratic signal in the hybrid/EV battery pack voltage sense B circuit.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The battery pack voltage sense B circuit reports a battery voltage measurement to the control module. P0B18 sets when that reading becomes intermittent or erratic, such as when a loose connection or unstable ground reference makes the signal drop out.
Common causes
Most likely first.
- Sensor connector not seated
- Noisy ground reference
- Connector with intermittent contact under vibration
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Save freeze-frame data and monitor live voltage sense B readings for sudden jumps or dropouts, noting when they occur.
- With the vehicle powered down as specified by the manufacturer, check that the sense B connector is fully seated and inspect its terminals and wiring for looseness, corrosion, or damage.
- Check for related voltage sensing or ground-reference codes that may indicate a shared electrical disturbance.
- Using the wiring diagram, inspect and test the sense B ground and reference connections for unstable contact.
- If the manufacturer's procedure permits, check the accessible harness for vibration-related dropouts and compare circuit behavior with the manufacturer's specification.
Common fixes
- Reseat and secure the voltage sense B connector.
- Clean or repair loose or corroded terminals.
- Repair damaged wiring or an unstable ground or reference connection.
- Replace the sensing component if its signal remains erratic after the circuit is verified.
Can I keep driving?
Keep trips short and avoid depending on electric power or charging until the voltage reading is stable, especially if the vehicle enters limp mode. Stop if power becomes unpredictable, since intermittent battery voltage data can trigger sudden system restrictions.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.