How do I set up a scope for a crankshaft sensor test?
Short answer: Back-probe the signal wire, ground the scope lead at the engine or battery negative, start around 5 volts per division for Hall sensors or a wider range for magnetic sensors, and use about 20 milliseconds per division while cranking or idling.
Start by identifying the sensor type. A Hall-effect or magnetoresistive sensor gives a square wave, usually switching between about 0 and 5 volts or battery voltage. A magnetic pickup gives an AC sine-like wave whose size grows with speed and can reach tens of volts at high rpm.
Connect the scope ground to a clean engine ground or battery negative, and back-probe the signal wire with the connector plugged in. Set the voltage scale so the whole wave fits, and set the time base so you see several revolutions; 10 to 50 milliseconds per division works at idle, slower while cranking. Use a trigger on a rising edge so the picture holds still.
Look for even spacing, a consistent amplitude, clean edges and the expected missing-tooth or sync gap. Dropouts, noise or uneven spacing point to the sensor, wiring, air gap or a damaged reluctor. Route leads away from ignition parts, belts and fans.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.