Parts for your 2003 Subaru Impreza-Camshaft sensor

2003 Subaru Impreza Camshaft Sensor — what it does, where it is, and how to look after it

Yes, the 2003 Subaru Impreza is fitted with a camshaft position sensor. Subaru’s Factory Service Manual for MY2003 Impreza (covering EJ-series H4 engines) lists the Camshaft Position Sensor (CMP) as a monitored input and defines DTCs such as P0340/P0341 for CMP circuit faults. Technical databases used by workshops, including Subaru’s technical information system and mainstream service information (e.g., Alldata/Mitchell), also show the CMP in wiring diagrams and engine management diagnostics for 2003 Impreza models. Most 2003 SOHC and non-AVCS WRX variants use a single CMP mounted on the left-hand cylinder head, some JDM-spec AVCS engines use a sensor on each bank.

On a 2003 Impreza, the camshaft sensor tells the ECU exactly where the cam is in its rotation. That little timing pulse lets the ECU fire the injectors sequentially, manage ignition timing cleanly at start-up, confirm timing correlation with the crank sensor, and, on AVCS-equipped engines, control variable valve timing. When the CMP signal goes missing or messy, drivers can see a hard start, a stumble just off idle, misfires, rough running, poor fuel economy, and the check engine light with codes like P0340 or P0341.

There’s no fixed replacement interval for the camshaft sensor, it’s a “replace-on-fault” item. As part of regular servicing, it’s smart to:

• Visually check the sensor connector and loom under the bonnet for brittle conduit, rubbed insulation, oil weeping, or corrosion every 20,000–30,000 km.
• During timing-belt work (around the 100,000 km mark typical for EJ engines), inspect the sensor body and wiring where it runs near covers and brackets.
• Keep oil leaks in check, oil in the connector can skew the signal.

If replacement’s needed, use a quality OEM-equivalent sensor and a fresh O-ring. It’s a simple driveway job on most variants:

1. Disconnect the battery negative.
2. Locate the sensor on the left-hand cylinder head (near the rear on SOHC, near the cam cover on WRX). Unplug the connector.
3. Remove the retaining bolt, withdraw the sensor, and swap the O-ring.
4. Refit the sensor, tighten the bolt to the factory spec, reconnect the plug, and reconnect the battery.
5. Clear codes and confirm live data shows stable cam and crank sync.

If a fresh sensor doesn’t sort it, check the crank sensor, timing-belt alignment, and wiring integrity—those are frequent accomplices. A quick scan-tool check of cam/crank correlation will save guesswork and keep the Impreza running sweet as.

Popular questions

Where is the camshaft sensor on a 2003 Subaru Impreza?
On most 2003 SOHC and non-AVCS WRX models, it’s on the left-hand cylinder head, secured by a single bolt, with a short wiring pigtail to the main loom. On AVCS-equipped engines, there can be a sensor on each head near the cam covers.

What are the symptoms of a failing camshaft sensor?
Common signs include longer crank time, intermittent stalling, misfires, hesitant acceleration, poor economy, and a check engine light with codes like P0340/P0341. If it’s bad enough, the ECU may drop into a fallback strategy that makes the engine feel flat.

Can it be driven with a bad camshaft sensor?
Sometimes, but it’s not ideal. The ECU may manage a limp mode using crank-only strategies, but starting and drivability can be crook, and fuel use will rise. It’s best to diagnose and fix promptly to avoid being stranded and to protect the catalytic converter from misfire damage.