How to test · Sensor

How to test a camshaft position sensor and check cam/crank timing

The CMP sensor tells the ECU which stroke each cylinder is on, for sequential injection and, on engines with variable valve timing, how far each camshaft has been moved. A failed sensor usually means a long crank (the ECU has to find position another way), a fault code and sometimes limp mode. A good signal in the wrong place relative to the crank points to timing: a stretched chain, a belt that jumped a tooth or a faulty cam adjuster.

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

In short

Most camshaft sensors are Hall-effect: check for a 5 V or 12 V supply, a ground with less than about 0.1 V drop, and a signal that switches cleanly between about 0 V and 5 V as the engine turns. On a scope, compare it with the crankshaft signal: the cam pattern must line up with the same crank teeth every time, or the timing is out.

Typical values

Check	Typical good	Suspect
Supply, ignition on	5 V or 12 V as specified	Missing or low
Ground, voltage drop while cranking	Below about 0.1 V	Above about 0.2 V
Signal while turning the engine	Clean switching, about 0 V ↔ 5 V	Stuck high, stuck low or missing pulses
Position against the crank signal	Same crank tooth every time, as on a known good engine	Shifted by teeth: timing or adjuster
Cam position deviation (live data, VVT engines)	Close to 0° at idle	Several degrees and rising: chain stretch or adjuster

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

Wiring: what you should measure

Hall-effect (most common)

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
Signal	About 0 V ↔ 5 V square wave as the camshaft turns

Before you start

Read the fault codes: a sensor circuit code (P0340 family) and a correlation code (P0016) point in different directions.
On variable valve timing engines, check the oil level and condition first: low or dirty oil upsets the cam adjusters.
Inspect the connector: on some engines oil wicks through the sensor into the connector and the wiring.

Multimeter

Ignition on: measure the supply at the sensor connector.
Measure the ground as a voltage drop to battery negative while cranking.
Back-probe the signal and turn the engine slowly by hand: the voltage should switch between low and high as the camshaft turns.

Oscilloscope (cam and crank together)

Channel A on the crankshaft sensor, channel B on the camshaft sensor; 0–10 V for Hall signals, about 20–50 ms/div at idle.
Count the crank teeth from the reference gap to the cam edge; compare with a known good capture or reference for the engine.
Rev the engine and watch whether the relationship moves on engines with cam adjusters (it should move only when the ECU commands it).
Check the cam signal for missing pulses, rounded edges or noise.

Scan tool

Watch specified and actual camshaft position or deviation on variable timing engines, at idle and while revving.
Run the cam adjuster actuator test if the tool supports it and watch the actual angle follow.

What it looks like on a scope

Good2 crank revolutions

Hall camshaft sensor at idle: clean 0–5 V pulses with sharp edges, the same pattern on every camshaft turn.

Fault: Missing pulse and noise2 crank revolutions

A pulse missing and noise on the low level: a failing sensor, a damaged trigger wheel or a poor connection. The ECU may lose sync or log a correlation fault.

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
Long crank, starts after a few seconds, CMP circuit code	No camshaft signal: the ECU has to find position another way
Clean cam signal, shifted against the crank by teeth	Timing chain stretched, belt jumped a tooth, or cam adjuster stuck (P0016)
Deviation grows with mileage on a chain engine	Chain stretch: plan the timing job before it jumps
Signal stuck at about 5 V	Sensor not switching, or no supply or ground
Oil inside the sensor connector	Oil wicking through the sensor: replace it and clean the connector and wiring

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

What happens when a camshaft position sensor fails?

Usually a long crank before the engine starts, a check engine light and sometimes reduced power. Many engines still run because the ECU can work from the crankshaft signal, but injection may switch to a less precise mode.

What is the difference between P0340 and P0016?

P0340 is a problem with the camshaft sensor circuit itself (no signal or out of range). P0016 means both signals are present but do not line up, which points to timing: a stretched chain, a jumped belt or a cam adjuster.

Can I drive with a bad camshaft sensor?

Often for a short distance, but the engine may stall or not restart, and if the real cause is a stretched timing chain, driving on can lead to the chain jumping and engine damage. Diagnose it soon.

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