A 2008 Toyota Avensis rolled in with a P2118 fault and a technician's note reading simply "no +bm voltage". When the engine control module loses its dedicated 12V supply to the throttle actuator, the fix is often far upstream of the throttle body itself.
The ETCS fuse and the missing power supply
The P2118 code specifically flags a problem with the throttle actuator control motor current range or performance. In this specific Avensis, the technician noted the lack of +BM voltage alongside the code. The +BM voltage is a dedicated 12V supply, usually routed through the Electronic Throttle Control System (ETCS) fuse, that powers the actuator control circuit inside the Engine Control Module.
If this fuse blows, the voltage drops. The ECM detects this loss (often registering below 4V), cuts current to the actuator, and throws the vehicle into a failsafe mode to prevent damage. Our diagnostic platform ranked a blown ETCS fuse as the 90 percent probable cause here, with high severity. A simple fuse inspection and voltage check is the required first step. Interestingly, on Toyota vehicles, this specific fuse failure is sometimes the aftermath of a reversed polarity jump start.
Tracing the wiring when the fuse survives
If the ETCS fuse is intact, the missing voltage problem moves to the wiring harness. We ranked a wiring or connector fault at a 70 percent probability. Open circuits, shorts, or high resistance in the harness can easily disrupt the +BM supply. Common physical failures include corroded pins, damaged insulation, frayed wires, and loose connections at either the throttle body connector or the ECM itself. Thermal stress near the engine block degrades these wires over time. A visual inspection, followed by continuity and voltage drop tests, isolates these physical circuit faults.
Internal motor failure and current draw
When the electrical supply and wiring hold up, the electric motor inside the throttle body assembly becomes the suspect. We ranked an internal throttle actuator control motor failure at 60 percent. Worn brushes, failing bearings, or cracked solder joints increase internal resistance. The motor then draws excessive current to move the throttle plate. If it pulls more than 9 amps for 200 milliseconds, the ECM interprets this as a fault and sets the P2118. Diagnosing this requires live data monitoring of the motor current and a direct motor resistance test.
The mechanical bind
Sometimes the electrical system is fighting a physical obstacle. Carbon buildup in the throttle bore creates physical resistance, causing the throttle plate to bind. The control motor works harder to overcome this friction, drawing the same excessive current that triggers the code. Ranked at 55 percent, this requires a visual inspection and cleaning of the throttle body to resolve.
Next steps in the bay
A missing +BM voltage on a Toyota throttle system is a clear directive to start at the fuse box, not the throttle body. Have you seen similar voltage supply drops triggered by jump starts in your own bays?