Crank sensor · VR · Hall

Crankshaft position sensor wiring

Without a crankshaft signal the ECU does nothing: no injection, no spark, no fuel pump after a few seconds. The crank sensor is the first thing to check on a no-start — and the easiest one to wire wrong.

Open the editor · ▶ Run the live demo

Inductive (VR) sensor — two wires and a shield

SIG and GND go to the ECU’s crank input pair; the sensor makes its own AC signal as the teeth pass.
Polarity matters: swapped wires shift the signal and the ECU may misread the trigger.
The shield goes to ground at the ECU end only, to keep ignition noise off the signal.

Hall sensor — three wires

Power (5 V or 12 V, depending on the sensor) and sensor ground from the ECU.
Signal: a square wave the ECU reads, often needing a pull-up inside the ECU.

In the simulator

WireForge does not draw the waveform, but it models what matters for wiring: the ECU reads the crank sensor, and with the engine speed above zero and the sensor connected it starts firing injectors and coils. Disconnect the sensor and the diagnostics say there is no crank signal.

Try it

Open the “ECU fuel injection” demo; note “no crank signal” at 0 rpm.
Drag the engine speed up: the ECU sees the crank signal and fires.
In the editor, disconnect the crank sensor wire and watch it stop.

Questions

Will a car start without a crank sensor?

Almost never: most ECUs need the crank signal to time injection and spark.

Does crank sensor polarity matter?

For inductive sensors, yes — reversed wires can make the ECU trigger on the wrong edge.

Where does the shield connect?

To ground at the ECU end only; grounding both ends makes a loop that picks up noise.

More guides

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