Parts for your 2021 Mazda 3-Camshaft sensor

2021 Mazda 3 camshaft sensor: purpose, care, and when to replace

Yes, the 2021 Mazda 3 uses a camshaft position (CMP) sensor. This is documented in Mazda’s BP-series Workshop Manual procedures for “Camshaft Position (CMP) Sensor—Removal/Installation and Inspection,” and it’s also listed in the Mazda Electronic Parts Catalogue for BP Mazda 3 engines (SKYACTIV‑G 2.0/2.5 and, where fitted, SKYACTIV‑X). Independent data sources used by workshops, such as Autodata/HaynesPro, likewise specify CMP sensor diagnostics and fault codes for this model.

The CMP sensor tells the engine control module exactly where the camshaft is in its rotation. That lets the Mazda 3 run true sequential fuel injection, dial ignition timing spot‑on, and control its dual S‑VVT (variable valve timing) smoothly. The result is easier starting, better fuel economy, lower emissions, and a nicer drive. On some engine variants there may be one or two CMP sensors (intake and exhaust), either way, they’re mounted on the cylinder head under the bonnet near the timing end.

• What it affects: cold and hot starts, idle quality, timing accuracy, VVT operation, fuel use, and emissions readiness.
• Typical symptoms when it’s crook: long crank or stalling, rough idle, flat spots, poor fuel economy, and a Check Engine Light with codes like P0340/P0341 (and P0365/P0366 if a second sensor is fitted).

As part of regular servicing, the CMP sensor isn’t a scheduled replacement item. The smart move is to keep an eye on the harness and connector for oil ingress or rubbing, and maintain high‑quality engine oil at the correct level—clean oil helps the VVT system the sensor is monitoring. If the car logs cam/crank correlation or CMP circuit codes, testing with a scan tool and a visual check should come first before swapping parts.

When replacement is justified, the job is straightforward for a trained tech and within reach of a capable DIYer:

• Confirm faults with scan data and a wiring check.
• Switch off, disconnect the battery (follow i‑Stop/M Hybrid battery procedures if equipped), remove the engine cover, and locate the sensor(s) on the head.
• Unplug the connector, remove the retaining bolt, replace the O‑ring if applicable, lightly oil it, fit the new sensor, and torque to workshop specs.
• Clear codes, perform any idle/idle‑stop relearns if required, and road test.

Using a genuine or OE‑quality sensor helps avoid false triggers and keeps the Mazda 3 happy over Aussie and Kiwi kilometres.

Popular questions about the 2021 Mazda 3 camshaft sensor

Where is the camshaft sensor on a 2021 Mazda 3?
It’s mounted on the cylinder head near the timing end under the engine cover. Depending on the engine, there may be one (typically intake) or two sensors (intake and exhaust). Access is usually from the top with basic hand tools.

On M Hybrid/SKYACTIV‑X variants, follow the correct battery disconnect/reconnect process so start‑stop and idle relearn procedures go smoothly after the job.

What fault codes point to a bad camshaft sensor?
Common codes include P0340/P0341 (camshaft position circuit/performance). If the engine has a second sensor, you may see P0365/P0366. Correlation codes like P0016 can also appear, though these can relate to timing or VVT issues—so test before replacing.

Does the camshaft sensor need regular replacement?
No scheduled interval. It’s replaced on condition—when diagnostics confirm a fault. Preventative care is about tidy wiring, clean connectors, and timely oil services to keep VVT stable and the sensor readings consistent.