What does it mean?
OBD II fault code B1318 is a manufacturer specific code that is defined by carmakers Ford and Jaguar as “Battery voltage low”, and is set when the PCM (Powertrain Control Module) detects that the battery voltage has fallen below a predefined level. While modern automotive electronics are designed to work optimally when the battery voltage is at its specified value, most electronic components/systems have the ability to operate normally at voltages that are far below the optimum battery voltage.
For instance, while starter motors work best when the battery is fully charged, most starter motors are designed to deliver their rated power (torque) at only 8-10 volts. Nonetheless, most electrical /electronic systems and components also have minimum operating voltages below which they simply will not work.
For instance, the starter motor solenoid requires a minimum voltage to overcome the tension of a spring to be able to close a circuit, while fuel pumps on return less fuel systems require a minimum voltage to be able to spin fast enough to deliver the minimum required fuel pressure to start the engine. However, many electronic systems also require minimum battery voltages to function properly even when the ignition is switched off.
These include, but are not limited to, the anti-theft/security system, as well as the PCM to maintain the KAM (Keep Alive Memory) circuits, which contains information on the idling speed and other basic engine operating data. As a practical matter however, there is little point in the PCM setting this code after the battery voltage has fallen to below a level where critical electronic systems have stopped working.
Therefore, in a fully functional system, the PCM will generally set this code and illuminate a warning light when the battery voltage approaches the critical, minimum level either when the ignition is switched on, or during normal operation of the vehicle.
Symptoms
- Slow cranking or a no-start condition, particularly after standing overnight
- Many unrelated warning lamps and stored codes appear across several modules at once
- Interior lamps dim, displays reset and stored settings are lost
- Windows, mirrors and seats operate slowly
- Automatic stop-start is disabled and a battery message appears on the display
Likely causes
- Weak, sulphated or simply aged battery that can no longer hold its resting voltage
- Low charging system output: worn alternator, slipping or glazed drive belt, failed regulator
- Corroded or loose battery terminals and ground straps
- Parasitic drain from a module that will not go to sleep, or from an aftermarket accessory
- Long periods standing, or repeated short journeys that never fully recharge the battery
- High resistance in the main power feed or a corroded fusible link
- Faulty battery monitoring sensor reporting a low value
How to fix it
- Load-test the battery and check its state of charge before doing anything else, this code is usually a symptom rather than a fault in itself
- Measure charging voltage at idle and again with the electrical loads switched on
- Clean and retighten the battery terminals and inspect the ground straps for corrosion
- Voltage-drop test between the alternator output and the battery positive post
- Perform a parasitic draw test once the vehicle has gone to sleep, then pull fuses to isolate the offending circuit
- Replace the battery or the alternator based on the test results, not on the code alone
- Register or code the new battery if the vehicle requires it, then clear codes from every module and recheck