P063B

What it means

P063B means the engine control unit has found the generator (alternator) voltage sense circuit 'A' signal out of range or not plausible. The control unit compares the voltage reading from the generator or charging system against its expected value, or against other voltage readings such as battery or system voltage, and the two disagree. How the sense circuit is wired and which module reads it varies by model and engine, so check the manufacturer wiring information.

Symptoms

• Battery or charging warning light on the dashboard
• Engine management light on
• Battery voltage reading too low or too high on the live data
• Flickering or dim headlights and interior lights
• Stop-start system disabled or behaving oddly
• Flat battery or slow cranking after standing

Possible causes

• Poor connection, corrosion or high resistance in the battery or generator sense wiring or connectorslikely
• Weak or failing battery, or loose or corroded battery terminals and earth straps, causing unstable system voltagelikely
• Faulty generator or its internal regulator giving incorrect output or sense signallikely
• Open circuit, short to earth or short to voltage in the sense wirepossible
• Faulty battery monitoring sensor or other charging control component, on vehicles that have onepossible
• Fault inside the engine control unit or a known outdated calibration, confirmed by the manufacturerrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting battery voltage, engine speed and load when the code set
2. Check the battery condition and terminal tightness, and clean any corrosion at the terminals and earth points
3. Measure battery voltage with the engine off, then at idle and at raised revs, and compare with the live data reading from the control unit
4. Inspect the generator wiring, plug and sense circuit for chafing, heat damage, corrosion and water ingress
5. Check the drive belt and tensioner for condition and tension, as a slipping belt can reduce generator output
6. Using the wiring diagram, test the sense circuit for continuity, resistance to earth and short to voltage, and check voltage drop on the supply and earth sides
7. Switch on a load such as headlights and rear screen heater and see whether charging voltage stays stable
8. Check for manufacturer service bulletins or software updates relating to the charging system on that model

How to fix

• Clean and tighten battery terminals and earth connections, and repair or replace any damaged cables
• Repair or replace damaged wiring or connectors in the generator sense circuit
• Replace the battery if it fails a load or capacity test
• Replace or overhaul the generator or regulator if output or sense signal is out of specification
• Replace the battery monitoring sensor if it is faulty and fitted
• Apply a manufacturer calibration update only if an outdated calibration is a documented cause for that model

Can I keep driving?

Nearby codes

• P063AGenericGenerator Voltage Sense Circuit A
• P063CGenericGenerator Voltage Sense Circuit A Low