Drive-by-wire · throttle motor · TPS
Electronic throttle body wiring: motor and position sensors
An electronic throttle has no cable: a motor opens the blade and two sensors report where it is. The ECU moves it to match a pedal that also has two sensors. Six wires on the throttle, six on the pedal — and the ECU must be built for it.
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The six throttle wires
- Motor + and motor −: both go to an H-bridge output of the ECU, which drives the motor in either direction. Neither goes to 12 V or ground directly.
- Position sensor: +5 V reference, sensor ground, and two signal tracks (TPS1 and TPS2).
- The two tracks run in different ranges or opposite directions, so the ECU can tell a real position from a fault.
- A spring holds the blade slightly open when the motor is unpowered — the limp-home position.
The pedal
The accelerator pedal has two tracks as well (APP1 and APP2), often on separate 5 V references and grounds. The ECU compares the two pedal tracks, the two throttle tracks, and the throttle against the pedal; if any pair disagrees it closes the throttle to limp mode.
Safety: why compatible hardware matters
- Only an ECU that supports drive-by-wire, with an H-bridge and the safety logic, may drive the motor. A relay or a PWM module is not a substitute.
- Throttle and pedal must be calibrated in the ECU (closed and open positions of every track) before the first start.
- Test limp mode on purpose: unplug one track with the engine idling — the ECU must react.
Draw it in WireForge
- Place an ECU module and two Throttle Position Sensor devices for TPS1 and TPS2 on the same +5 V and sensor ground.
- Add the throttle motor as a Custom block with M+ and M− wired to two ECU outputs.
- Simulate and move the TPS sliders: click each SIG wire to compare the two tracks.
- The simulator does not model the H-bridge or the ECU’s safety logic; add Text notes for the calibration values.
Questions
Can I convert a cable throttle ECU to drive-by-wire?
Only if the ECU has drive-by-wire support: an H-bridge output and the safety strategy. Otherwise use a cable throttle or a dedicated DBW controller.
Why two sensors?
Redundancy. A single failed sensor could command full throttle; with two the ECU detects the disagreement and goes to limp mode.
Is the motor polarity important?
Yes — swapped M+ and M− make the ECU drive the blade the wrong way, which it detects as a fault. Wire them as the ECU and throttle documentation show.