P06B4

What it means

P06B4 means the engine control module has detected that the voltage on sensor power supply B (a regulated reference voltage, typically 5 V, that feeds a group of sensors) is lower than expected. The module monitors this supply and sets the code when the voltage falls below its allowed range. Which sensors share supply B depends on the make, model and engine.

Symptoms

• Engine warning light on
• Poor running, hesitation or reduced power
• Car in limp mode with limited throttle response or revs
• Rough idle or stalling
• Difficulty starting or no start
• Other sensor fault codes stored at the same time

Possible causes

• Short to earth in the wiring of the shared 5 V reference circuit, for example chafed insulationlikely
• A faulty sensor on supply B pulling the reference voltage down internallylikely
• Corroded, damaged or loose connector terminals on the sensor or control module sidepossible
• Water ingress or contamination in a sensor connector or harness junctionpossible
• Poor control module power or earth supply affecting the internal regulatorpossible
• Faulty engine control module with a failed internal reference voltage regulatorrare

How to diagnose

1. Read all stored and pending codes and note freeze frame data; look for other sensor circuit codes that share the same supply, as the pattern points to the affected circuit
2. Check the manufacturer wiring diagram to identify which sensors are on supply B for this model and engine
3. Visually inspect the harness and connectors for chafing, rubbed insulation, corrosion, water and bent or pushed-back pins
4. Check the battery condition and charging voltage, and the control module power and earth connections
5. With the ignition on, measure the reference voltage at the sensor connectors and compare with specification
6. Unplug the sensors on supply B one at a time while monitoring the reference voltage; if it returns to normal, the last sensor unplugged is faulty
7. Test the reference wire for short to earth and for resistance between circuits with the module disconnected, following the wiring diagram
8. If wiring and sensors test good and the voltage is still low at the module, check for a calibration update and then consider the control module

How to fix

• Repair or replace the damaged wiring section causing the short to earth
• Replace the faulty sensor that is pulling the supply voltage down
• Clean or repair corroded connectors and terminals, and dry and seal any area where water has got in
• Restore good power and earth connections to the control module
• Replace or repair the control module only after the wiring and sensors have been proven good, and carry out any required programming

Can I keep driving?

Nearby codes

• P06B3GenericSensor Power Supply B Circuit/Open
• P06B5GenericSensor Power Supply B Circuit High