Parts for your 2004 Subaru Impreza-Camshaft sensor

2004 Subaru Impreza Camshaft Sensor

Based on the Subaru MY2004 Impreza Factory Service Manual (Engine/ECM Diagnostics), the Subaru FAST electronic parts catalogue, and common OEM catalogues (Denso/NTK) as well as Autodata/Haynes references, the 2004 Subaru Impreza is fitted with a camshaft position sensor (often called the “phase” sensor). Non-AVCS engines typically use a single sensor, while some AVCS-equipped turbo variants use one per bank.

On a 2004 Impreza, the camshaft sensor lets the ECU know exactly where the cam is relative to the crank, so it can fire the injectors and ignition at the right time. That means easier starts, clean idle, proper power delivery, and lower emissions. If the signal goes missing or messy, the car may hard-start, misfire, hesitate, or drop into a limp-home strategy. The check engine light usually logs codes like P0340 or P0341.

Location varies by engine: most non-AVCS EJ motors have a single sensor on the left-hand cylinder head near the timing belt cover, AVCS turbo variants can have one on each head. Across the board, access is straightforward under the bonnet with basic tools.

It’s not a routine replacement item, but it’s worth checking during scheduled servicing—especially on higher-kilometre cars. Look for oil ingress at the connector, brittle wiring near the timing covers, and loose or corroded pins. A quick visual once-over when changing the timing belt or doing spark plugs is smart practice.

When replacement is needed, stick with quality OEM-equivalent parts. The job usually involves disconnecting the battery, unplugging the sensor, removing a single retaining bolt, swapping the O-ring, and refitting. Lightly oil the new O-ring so it seats without nicking, route the loom away from hot or moving parts, and tighten the fastener to the specification in the Subaru service manual. Clear any stored codes and confirm live data or cam/crank synchronisation with a scan tool.

Common signs it’s on the way out include:

• Crank–no start or long crank when hot or cold
• Rough idle, hesitation, or flat spots on acceleration
• Random stalling and an illuminated MIL with P0340/P0341

A failing sensor won’t usually damage the engine, but it can leave the driver stranded. If in doubt, rule out wiring/connector faults first, then replace the sensor. For WRX and STi models, confirm whether one or two sensors are fitted before ordering parts.

Where is the camshaft sensor on a 2004 Impreza, and does WRX/STi differ?

Most non-AVCS 2.0/2.5-litre engines have a single sensor on the left-hand cylinder head near the timing belt cover. Some turbo AVCS variants (notably STi and certain markets) use a sensor on each bank. A quick check of the VIN/engine code or the Subaru FAST parts listing will confirm the exact setup.

What are the usual symptoms and fault codes?

Common symptoms are hard starting, random stalling, misfires, and poor throttle response. The ECU often logs P0340 (Camshaft Position Sensor Circuit) or P0341 (Camshaft Position Sensor Range/Performance). Scan live data to verify cam/crank sync before replacing parts.

Can it be cleaned, or should it be replaced?

If the issue is oil or corrosion on the connector, cleaning and reseating can restore a solid signal. If the sensor itself is internally failing or the signal is unstable despite good wiring, replacement is the reliable fix. Stick to OEM-quality to avoid intermittent gremlins.