Crankshaft and camshaft position sensors are behind a huge share of no-start, stall, and hard-start complaints — and they're frequently replaced when the real fault is wiring, a damaged reluctor wheel, or a timing problem. The trick is knowing which of the two sensor types you have, because a magnetic sensor and a Hall-effect sensor are tested completely differently. This guide covers both, what the common codes mean, and how to separate a bad sensor from the things that imitate one.
What each sensor does
The crankshaft position (CKP) sensor is the master timing reference: it tells the ECM engine speed and exactly where the crankshaft is, which the ECM uses to fire ignition and injection. Lose it and the engine usually won't start or stalls. The camshaft position (CMP) sensor reports where the camshaft is, which the ECM needs for sequential fuel injection, cylinder identification, and variable valve timing. A CMP fault often still lets the engine start (in a degraded mode) but can cause long crank times and drivability faults.
First: which type is it?
- Magnetic / inductive (passive) — typically 2 wires, generates its own AC voltage as the reluctor teeth pass. No reference voltage needed. Amplitude rises with engine speed.
- Hall-effect (active) — typically 3 wires: a reference voltage (5 V or 12 V), a ground, and a signal. Outputs a clean digital square wave. Needs power and ground to work.
Count the wires and check the diagram before testing — it determines every step that follows.
Testing a magnetic (2-wire) sensor
- Resistance: measure across the two terminals and compare to spec (commonly a few hundred to ~1,200 Ω). Open or out-of-spec = failed sensor.
- AC output: set the meter to AC volts and crank — a healthy sensor produces an AC signal (often 0.5–2 V AC or more) that rises with speed. No output while cranking with good resistance points to the reluctor or air gap.
- Air gap & reluctor: inspect the tone/reluctor wheel for damaged or missing teeth, rust, or debris, and confirm the air gap. A cracked or contaminated reluctor produces the same symptoms as a bad sensor — the same lesson as ABS tone-ring failures.
Testing a Hall-effect (3-wire) sensor
- Power & ground: back-probe the connector and confirm the reference voltage and a good ground are present (see how to back-probe a connector and testing a 5V reference). No power or ground = wiring fault, not the sensor.
- Signal: with a scope, watch for a clean square wave while cranking; with a DVOM, a toggling voltage. A flatline with good power/ground points to the sensor or reluctor.
- Reluctor: as with magnetic sensors, inspect the trigger wheel for damage.
What the common codes mean
- P0335 / P0336 — crankshaft position sensor circuit / range. Often the sensor, but verify wiring and the reluctor.
- P0340 / P0341 / P0345 — camshaft position sensor circuit / range / bank 2.
- P0016 / P0017 — crankshaft/camshaft correlation. These mean the cam and crank are out of their expected relationship — frequently timing chain stretch or a VVT/oil-control problem, not a failed sensor. Don't just replace the sensor on a correlation code.
Treat circuit/range codes as "test the sensor, wiring, and reluctor," but treat correlation codes as a timing investigation. For circuit codes generally, see diagnosing sensor circuit high/low codes.
FAQ
What's the difference between the crankshaft and camshaft sensor?
The crankshaft (CKP) sensor is the master timing/speed reference — lose it and the engine usually won't run. The camshaft (CMP) sensor reports cam position for sequential injection, cylinder ID, and VVT — a fault often allows a degraded start but causes hard starting and drivability issues.
How do I know if my sensor is magnetic or Hall-effect?
Count the wires and check the diagram: a 2-wire sensor is usually a passive magnetic type (test resistance and AC output), while a 3-wire sensor is a Hall-effect type that needs a reference voltage and ground (test power, ground, and the square-wave signal).
Can a no-start be the crankshaft sensor?
Yes — a failed CKP sensor (or its wiring, or a damaged reluctor) commonly causes a crank-no-start because the ECM loses its timing reference. Confirm with resistance/AC output (magnetic) or power/ground/signal (Hall) while cranking before replacing.
Does P0016 mean I need a camshaft sensor?
Not usually. P0016 is a crank/cam correlation code — the cam and crank are out of their expected relationship, often from timing chain stretch or a VVT oil-control problem. Investigate timing before replacing the sensor.