RIDEX Engine Knock Sensor with Cable • 3921K0044

RIDEX 3921K0044 Engine Knock Sensor with Cable

Replacement RIDEX engine knock sensor for Mazda MX-5 Mk3/NC 1.8 and 2.0-litre petrol models, plus selected Mazda 3, Mazda 5 and Mazda 6 petrol applications listed in the compatibility table.

The knock sensor detects the characteristic engine-block vibration caused by detonation or uncontrolled combustion. It sends this information to the engine control unit, allowing ignition timing to be adjusted to help protect the engine while maintaining suitable performance and efficiency.

The sensor is mounted directly to the engine block or a dedicated engine mounting boss. One knock sensor is required per engine and one sensor is supplied with its attached cable and electrical connectors.

Common symptoms of knock-sensor failure include an illuminated engine-management light, stored knock-sensor circuit or signal fault codes, reduced engine performance, increased fuel consumption and conservative ignition timing or reduced-power operation.

• Part type: Engine knock / detonation sensor
• Primary use: Detects abnormal combustion vibration and sends a signal to the engine control unit
• Location: Engine block or dedicated knock-sensor mounting boss
• Supplementary contents: With attached cable
• Cable length: 300 mm
• Number of connectors: 2
• Approximate weight: 0.06 kg
• EAN: 4059191804283
• Quantity per vehicle: 1
• Quantity supplied: 1
• Brand: RIDEX
• Part No.: 3921K0044
• Designed as an aftermarket replacement for the applications listed in the compatibility table

Fitment advice: This sensor corresponds with the Mazda LF01-18-921 and LF02-18-921 reference families. It is suitable for the confirmed Mazda applications shown in the compatibility table. Later SKYACTIV applications and Mazda MX-5 Mk4/ND models use different knock-sensor references and are not included. For imported, modified or previously repaired cars, matching the part number, cable length and connector arrangement on the sensor being replaced is recommended.

Other items to consider: When changing this part, you may also want to consider purchasing intake-manifold gaskets where manifold removal is required, replacement wiring clips, electrical-contact cleaner, engine-bay harness repair components and any disturbed hose clips or seals.

Useful tools / consumables: Socket and spanner set, extension bars, torque wrench, electrical-connector tools, intake-manifold tools where required, electrical-contact cleaner, workshop towels and suitable protective gloves.

Difficulty guide: DIY Difficulty: Moderate to Advanced. Access can require removal of intake-system components or the intake manifold, depending on the vehicle. Correct mounting-surface preparation and tightening torque are important because the sensor relies on direct mechanical contact with the engine.

Why RIDEX? RIDEX parts are aftermarket replacement components designed to provide a cost-effective repair option for everyday vehicle maintenance and refurbishment. They are intended to replace the original component on the applications listed, helping restore function while keeping repair costs sensible.

What’s in the box: One RIDEX engine knock sensor with attached 300 mm cable and two-connector harness arrangement.

Installation notes: Allow the engine to cool and disconnect the battery before starting work. Remove the intake ducting, manifold or surrounding components required for access. Disconnect the sensor wiring and remove the old sensor carefully. Clean the mounting boss so the replacement sensor sits flat against bare, undamaged metal. Do not apply sealant, grease or excessive corrosion treatment between the sensor and engine. Install the sensor in the correct orientation and tighten it to the applicable vehicle specification, as incorrect torque can affect sensor sensitivity. Route the cable away from hot or moving components, reconnect the electrical plugs and refit all removed parts. Clear stored fault codes where appropriate and confirm correct operation after installation.