Fault code B1318 – battery voltage low

Fault code B1318 is called “Battery Voltage Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code B1318

Fault code B1318 refers to manufacturer specific faults, in this case Ford, Mazda and Jaguar. Defined as “low battery voltage”, it is set when the control module detects that the battery voltage has dropped below a preset level.

Fault code B1318 – battery voltage low

Modern automotive electronics are designed to operate optimally at a given battery voltage.  Therefore, most electrical systems and components also have a minimum operating voltage below which they simply will not work.

For example, the starter solenoid requires a minimum voltage to overcome the spring tension to close the circuit. Fuel pumps in reduced fuel return systems require a minimum voltage. To spin fast enough to provide the minimum fuel pressure needed to start the engine.

As a practical matter, it does not make sense for the PCM to set code B1318 after the battery voltage has dropped below a level. At which point critical electronic systems stop working.

Therefore, in a fully functional system, the PCM usually sets this code and turns on the warning light. When the battery voltage approaches the critical minimum level either when the ignition is turned on or during normal vehicle operation.

Symptoms of vehicle malfunctions

The main signal that an error B1318 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Most likely, there will be no symptoms, except for the stored fault code and illumination of the “Check engine” lamp on the instrument panel.
  2. Sometimes unstable operation of some automobile electrical systems may occur.

Fault B1318 is serious, as it can directly affect the safety of driving. It is recommended to eliminate this fault as soon as possible.

Factors that can cause this error code

The error code B1318 can mean that one or more of the following problems have occurred:

  • The battery may be undercharged or in poor condition.
  • Using a battery with the wrong rating.
  • The alternator drive belt may be loose.
  • Alternator cables or connections may be damaged.
  • The alternator may be defective.
  • Improper or incorrect installation of aftermarket electrical equipment.
  • Malfunction or failure of the PCM, or other control module.

How to fix or reset OBD-2 code B1318

Some suggested steps for troubleshooting and fix the error code B1318:

  1. Study the Technical Service Bulletins (TSB). For known problems with your particular vehicle.
  2. Make sure the battery has the correct voltage, check this value against that specified by the manufacturer in the owner’s manual.
  3. Check that the alternator drive belt and alternator electrical connections are in good working order.
  4. If you find problems with any of these components, make the necessary repairs.

Diagnose and repair of problems

A faulty battery is a common cause of code B1318, so you can start diagnosing with it. But you should understand that a damaged or faulty battery is often just a symptom of a problem in another part of the electrical system.

For this reason, it is important that if a faulty battery is detected, to proceed with a full diagnosis of the charging system. Furthermore, if the charging system is fully functional, it is important to locate and correct the source of the dead battery before the vehicle is returned to service. To prevent this code and related symptoms from reappearing.

Therefore, it is not unreasonable to check the alternator and drive belt, as well as the wiring harnesses and connectors. If any faults are found, they should be corrected to prevent a recurrence of fault B1318.

On which vehicles does this problem occur most frequently

Fault code B1318 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Ford (Focus, Fusion)
  • Mazda

Fault code B1318 can sometimes be found with other errors. The most common are the following: B1315, B1317, B2103, C1165, C1175, U261B.


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