What it means
The voltage in sensor power supply B is below the expected range. This may affect components supplied by that circuit; which ones depends on the vehicle.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Sensor power supply B feeds a vehicle-dependent group of sensors through a module-managed rail. P06B4 sets when the rail voltage falls below the expected range, often because the supply line is shorted to ground or a connection has excessive resistance.
Common causes
Most likely first.
- Supply line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
How to diagnose it
- Scan all modules, save freeze-frame data, and note companion faults that could identify sensors sharing supply B.
- Review live data for those sensors to see which readings fail together and whether the problem is present now.
- Inspect supply B wiring and connectors for chafing, corrosion, moisture, loose pins, or damage near the affected sensors and module.
- Use the wiring diagram to measure supply B as directed by the manufacturer and check for a short to ground or high resistance.
- If the harness checks out, test the module output and connected sensor loads according to the manufacturer's specification.
Common fixes
- Clean and secure a corroded or loose supply B connector.
- Repair chafed wiring or a supply B short to ground.
- Repair a sensor or branch that testing shows is pulling supply B low.
- Repair or replace the module if its supply B output is confirmed faulty.
Can I keep driving?
A low supply B rail may affect several sensors and cause poor running, reduced power, or stalling. Avoid high-speed or demanding driving, and stop if engine operation becomes unreliable.
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.