BCU 000168.18 – Control Unit Supply Voltage Too Low at Moderate Engine Speed. John Deere System Advisory.

BCU 000168.18 (BCU 168.18)

Code: 000168.18

Shortcode: 168.18


Error code BCU 000168.18 is activated when the Basic Control Unit (BCU) of a John Deere vehicle detects that the supply voltage has fallen below 11.2 volts while the engine speed is above 500 rpm. This indicates an insufficient charging rate from the alternator or other related issues in the electrical system that are unable to maintain adequate voltage levels during moderate engine operation.


The BCU may respond to this low voltage condition by reducing the operational capacity of electrical systems or by triggering alerts and warnings on the vehicle’s dashboard to notify the operator of potential issues in maintaining necessary electrical power.


  • Inspect the Charging System: Thoroughly check the alternator and voltage regulator for proper operation. The alternator should produce sufficient voltage to maintain at least 11.2 volts at engine speeds above 500 rpm.
  • Check Electrical Connections and Grounds: Examine all connections related to the charging system, including battery terminals, alternator connections, and ground connections. Ensure they are clean, tight, and free of corrosion.
  • Evaluate the Battery’s Health: Assess the battery’s capacity to hold a charge. A failing battery may not sustain adequate voltage levels even if the charging system is functioning correctly.
  • Inspect Drive Belts: Check the condition and tension of the alternator drive belt. A loose or worn belt can impede the alternator’s ability to generate enough power at lower engine speeds.
  • Reset and Recalibrate the BCU: After addressing potential issues, reset the BCU to clear the diagnostic codes. Recalibrate if necessary and test the system to ensure the voltage remains stable under different operating conditions.


Regular maintenance of your John Deere’s electrical system, including the charging system and battery, is crucial to avoid low voltage issues that can impair vehicle performance and reliability. Addressing these issues promptly ensures that the vehicle operates efficiently, reducing downtime and potential damage to sensitive electrical components.