Buy Subaru WRX Camshaft Position Sensors

The camshaft position sensor (CMP) sits on each cylinder head of the WRX's flat-four boxer engine and counts gear teeth on the cam to report its angle to the engine control unit (ECU). (Wikipedia)
Together with the crankshaft sensor, it sets fuel-injector timing and spark advance so power and mileage stay on target. (Wikipedia)

Most Subaru CMP sensors are Hall-effect devices that create a digital on/off signal as the cam gear passes a magnet. (Wikipedia)
The ECU watches both cam and crank signals; if they drift too far apart, it stores timing-correlation codes such as P0016 or P0017. (clubwrx.net)

On 2015-2021 WRX and WRX STI models (FA20DIT or EJ257 engines), there are four sensors-two per head:

• Bank 1 = passenger side (cyl 1) * Bank 2 = driver side. (JustAnswer, Reddit)
• ÒSensor AÓ sits high on the head for the intake cam; ÒSensor BÓ is low for the exhaust cam. (, pedrosboard.com)

• Flashing or steady check-engine light, often P0340, P0345, P0016, P0017. (clubwrx.net, Reddit)
• Hard starting, stalling, or no-start while cranking. (familyhandyman.com, parts.subaru.com)
• Poor acceleration and high fuel use because timing is stuck in limp mode. (familyhandyman.com)

1. Unplug the 3-pin connector and measure resistance across the outer pins; Subaru spec is roughly 1 kΩ - 4 kΩ at 68 °F. (subaruforester.org, ultimatesubaru.org)
2. Back-probe the signal wire with a scope; you should see square waves that match engine speed. (subaruoutback.org)
3. Swap the suspected sensor to the other bank; if the code follows, the sensor is faulty. (Reddit)

1. Disconnect the negative battery cable.
2. Pull the engine cover for better access.
3. Press the plastic tab and unplug the sensor.
4. Remove the single 10 mm bolt, wiggle the sensor free, and replace the O-ring.
5. Reinstall and torque the bolt to 6.4 Nm / 4.7 ft-lb. (legacygt.com, static.nhtsa.gov)
6. Clear codes and road-test; the ECU will relearn timing within a few minutes. (YouTube)

← scroll table horizontally →

• Active Valve Control System (AVCS) adjusts cam timing using oil control solenoids and relies on accurate CMP data. (Wikipedia)
• Crankshaft Position Sensor (CKP) works with CMP; both signals create a full 720-degree timing map. (Wikipedia)

Keep engine oil clean; sludge can block AVCS passages and trigger false cam-sensor codes. (static.nhtsa.gov)
Inspect harness connectors for oil wicking or broken clips during every spark-plug change (60 k mi). (Reddit)

Q: Why does my WRX show code P0340 right after an oil change?
A: If oil drips into the sensor connector, it can short the signal. Clean the plug and clear the code.

Q: Can I keep driving with a bad cam sensor?
A: The car may run, but power and fuel economy suffer, and it could stall at lights-replace it soon. (familyhandyman.com)

Q: How many cam sensors does a 2015-2021 WRX have?
A: Four-one for each intake and exhaust camshaft on both cylinder heads. (Reddit)

Q: Is the cam sensor the same part as the crank sensor?
A: No; they look alike but read different toothed wheels and are not interchangeable.

Q: What tools do I need to change it?
A: Only a 10 mm socket, small ratchet, and torque wrench for the bolt. (YouTube)

Q: Will a failing cam sensor hurt my turbo?
A: Not directly, but bad timing can cause misfires that raise exhaust temps, which may strain the turbo. (clubwrx.net)

Q: Do aftermarket performance cams need different sensors?
A: No, but you may need ECU tuning so the new cam profile aligns with the factory timing map. (Wikipedia)

By understanding how the Subaru WRX camshaft position sensor works, spotting early warning signs, and following the easy replacement guide, you can keep your boxer engine happy and healthy for years to come.