What the Crankshaft Position Sensor Does
The crankshaft position sensor (CKP sensor or crank sensor) monitors the rotation of the crankshaft and sends a signal to the engine control unit (ECU). This signal tells the ECU two critical things: the engine's rotational speed (RPM) and the precise position of the crankshaft at any given moment.
The ECU uses this data to time fuel injection and ignition spark. Without a signal from the crank sensor, most modern engines simply won't fire — even if fuel, spark, and compression are all present.
How Crank Sensor Failure Shows Up
Crank sensor faults can be intermittent, which makes them particularly frustrating to diagnose without the right tools.
- Engine cranks normally but will not start — no check engine light may be present initially
- Intermittent no-start — works fine most of the time but fails to start occasionally, often when hot
- Engine stalls while driving and may or may not restart
- Engine hesitation or rough idle before complete failure
- Check engine light with codes P0335 or P0336 (crankshaft position sensor circuit faults) — requires a scan tool to read
The heat-related pattern is particularly common: a marginal crank sensor may work fine when cold but fail after the engine reaches operating temperature, causing a "hot no-start" that puzzles drivers because the car starts fine in the morning.
Diagnosis
A scan tool will reveal CKP-related fault codes. Some mechanics also use an oscilloscope to check the quality of the sensor's signal pattern — a weak or erratic signal points to a failing sensor even before it fails completely.
A simple resistance check with a multimeter can also be performed on the sensor itself, though this won't catch intermittent faults.
Replacement Cost in NZ
Crank sensor replacement is usually straightforward — the sensor is typically located on the engine block near the crankshaft pulley or flywheel. On most Japanese import vehicles:
- Parts: $60–$180 NZD for the sensor
- Labour: $60–$150 NZD (30 min–1 hour job)
- Total: $120–$330 NZD
On some European vehicles where access is restricted, labour can be higher. Always use an OEM or reputable aftermarket sensor — cheap sensors have a high failure rate and can introduce new running problems.
Related Sensor: Camshaft Position Sensor
The camshaft position sensor (CMP sensor) works alongside the crank sensor. A failed cam sensor produces similar symptoms and often similar fault codes (P0340, P0341). The ECU needs both signals to run correctly on most modern engines. If one fails, the other is sometimes replaced at the same time as preventative maintenance, especially on high-mileage vehicles.