How to test · Sensor

How to test a crankshaft position sensor: multimeter and scope

The CKP sensor gives the ECU engine speed and crankshaft position from a toothed reluctor wheel, often 60-2 (58 teeth and a gap of two). With no signal most engines get no injection and no spark, so the classic symptom is "cranks but will not start", often with the rev counter not moving while cranking. A weak or noisy signal causes stalling, misfires or a cut-out when hot.

Updated 25 Oct 2026 · written by ipacen; typical values, not manufacturer data

In short

Find out the type first. An inductive (2-wire) CKP sensor usually measures about 200–2,000 Ω and makes an AC signal that should reach at least about 0.5 V AC while cranking, rising with rpm. A Hall-effect (3-wire) sensor needs a 5 V or 12 V supply and a good ground, and its signal should switch cleanly between about 0 V and 5 V. On a scope both should show a steady pattern with a clear gap for the missing teeth.

Typical values

Check	Typical good	Suspect
Inductive: resistance, sensor unplugged	About 200–2,000 Ω, to the specification	Open (OL) or close to 0 Ω
Inductive: AC output while cranking	At least about 0.5 V AC, more as rpm rises	Below about 0.3 V AC, or erratic
Hall: supply, ignition on	5 V or 12 V as specified	Missing or low
Hall: signal while turning the engine	Clean switching, about 0 V ↔ 5 V	Stuck high, stuck low or noisy
Air gap (where adjustable)	To specification, often about 0.5–1.5 mm	Too large, or swarf on the tip

Typical ranges, not manufacturer data: check the specification for the engine.

Which type is it?

Inductive (variable reluctance)Two wires, often in a shielded cable. It makes its own AC voltage as the teeth pass, and the amplitude rises with speed. No supply from the ECU.

Hall-effect or magnetoresistiveThree wires: supply, ground and signal. It gives a square-wave signal whose height does not change with speed, so it works down to very low rpm.

Wiring: what you should measure

Inductive (2-wire)

Wire	What you should see
Signal + and signal −	AC voltage while cranking; about 200–2,000 Ω between them with the sensor unplugged
Either pin to ground	Open circuit: a short to ground kills or weakens the signal
Shield (if fitted)	Grounded at one end only, usually at the ECU

Hall-effect (3-wire)

Wire	What you should see
Supply	5 V or 12 V with the ignition on
Ground	Less than about 0.1 V drop to battery negative while cranking
Signal	Switches between about 0 V and 5 V (sometimes 12 V) as the engine turns; pulled up by the ECU

Before you start

Read the fault codes and freeze frame, and watch rpm in live data while cranking: 0 rpm while cranking points to the CKP circuit.
Inspect the sensor: metal swarf on the magnetic tip, oil in the connector, chafed wiring near the exhaust or the flywheel.
Identify the type from the wiring diagram or the number of wires before you measure.

Multimeter: inductive sensor

Unplug the sensor and measure the resistance across its two pins; compare with the specification.
Measure from each pin to ground: it must be open circuit.
Back-probe the connector and measure AC volts while cranking.
Repeat the AC measurement at the ECU connector to prove the wiring in between.

Multimeter: Hall-effect sensor

Ignition on: measure the supply at the sensor connector.
Measure the ground side as a voltage drop to battery negative while cranking; it should be below about 0.1 V.
Back-probe the signal and turn the engine slowly by hand: the voltage should switch between low and high.

Oscilloscope

Channel A on the signal wire (back-probe, do not pierce the insulation), scope ground on the engine block or battery negative.
Inductive: start at ±10 V and 20 ms/div while cranking. Hall: 0–10 V DC, 5–20 ms/div.
Look for an even pattern, the reference gap once per revolution, and no missing or distorted teeth.
With channel B on the camshaft sensor, check that the cam pattern always sits at the same crank tooth (timing correlation).

What it looks like on a scope

Good200 ms (cranking)

Inductive CKP while cranking: an AC wave that grows as the engine speeds up, a flat section at the missing teeth and a bigger swing right after them.

Fault: Weak and noisy200 ms (cranking)

Low amplitude with noise: too big an air gap, swarf on the tip, a weak magnet or a damaged shield. The ECU can lose sync at cranking speed.

Typical shapes drawn by ipacen, not a capture from one car: amplitude and timing vary with the engine, the sensor and the rpm.

What the readings tell you

You find	It usually means
No rpm in live data while cranking and no AC output	Open sensor coil or wiring, or a signal shorted to ground: check resistance and the wiring back to the ECU
Good signal at the sensor, none at the ECU	Broken wire or bad connector between them
Low amplitude that improves after cleaning the tip	Metal swarf on the magnetic tip or an air gap that is too big
Teeth missing or an extra glitch in the pattern	Damaged reluctor wheel, or a reluctor ring that has moved
Hall signal stuck at about 5 V	The sensor is not switching (dead, or no supply or ground): you only see the ECU pull-up
Hall signal stuck at 0 V	Signal wire shorted to ground, or a shorted sensor
Cuts out when hot, fine when cold	Typical of a failing sensor: scope it hot, or warm it carefully with a heat gun

Known engine problems behind these codes

Mazda 2.2 diesel: Timing chain stretchMazda · typically 120,000–220,000 km 1.2/1.4 TSI EA111: Timing chain stretch and tensionerVolkswagen, Audi, Skoda, Seat · typically 60,000–160,000 km 1.8/2.0 TFSI EA888: Timing chain tensioner failure and chain jumpAudi, Volkswagen, Skoda, Seat · typically 60,000–180,000 km 1.2 PureTech: Timing belt breaking down in the oilPeugeot, Citroën, DS, Opel · typically 60,000–150,000 km 1.0 EcoBoost: Timing belt in oil wearing earlyFord · typically 100,000–200,000 km 1.6 THP/Prince: Timing chain stretch, tensioner and guidesMini, BMW, Peugeot, Citroën, DS · typically 60,000–160,000 km 1.2 TCe: Timing chain stretch after running low on oilRenault, Dacia, Nissan, Mercedes-Benz · typically 60,000–140,000 km Volvo 5-cyl petrol: Timing belt, tensioner and idler pulleyVolvo, Ford · typically 120,000–200,000 km

Questions mechanics ask

Can a car start with a bad crankshaft position sensor?

Usually not if the signal is lost completely, because most engines need it to inject fuel and fire the coils. Some engines start on the camshaft signal alone after a long crank. A weak sensor often still starts the engine but makes it stall or cut out, especially when hot.

What resistance should a crankshaft position sensor have?

An inductive (2-wire) sensor typically measures about 200–2,000 Ω depending on the design; check the specification for the engine. A Hall-effect (3-wire) sensor cannot be tested by resistance: check the supply, the ground and the switching signal instead.

How do I know if a CKP sensor is inductive or Hall-effect?

Count the wires and check the wiring diagram. Two wires (sometimes with a shield) is usually inductive; three wires with a 5 V or 12 V supply is Hall-effect or magnetoresistive.

Should the rev counter move while cranking?

On most cars, yes. If the rev counter or the rpm in live data stays at zero while cranking, the ECU is not seeing a crankshaft signal.

Values are typical, not manufacturer data. Always follow the service information for the vehicle and work safely.