Knock Sensor Assembly – Fits Volvo Penta OMC Cobra Sterndrives (Replaces 3854905, 18-7679)

Product Details

This Knock Sensor Assembly is designed for Volvo Penta and OMC Cobra sterndrive marine engines. It provides accurate engine knock detection to protect your engine from detonation damage and ensure optimal performance across a wide range of operating conditions.

This aftermarket assembly directly replaces Volvo Penta part number 3854905, OMC Cobra 3854905, Sierra 18-7679, and Mallory 9-33504.

• Precision knock detection for engine protection
• Built to withstand marine environments
• Direct-fit replacement for OEM sensors

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Technical Specs

Type

Marine Knock Sensor

Engine Type

OMC / VOLVO PENTA Sterndrive

Application

Sterndrive marine engines

OEM Reference

3854905

What's in the Box

• 1 × Marine Knock Sensor

Installation Notes

1. Disconnect the battery negative terminal before beginning work.
2. Locate the original knock sensor on your engine block, typically mounted on the intake manifold or block side.
3. Disconnect the electrical connector from the old sensor.
4. Remove the mounting bolt and carefully extract the old knock sensor.
5. Clean the mounting surface to ensure proper contact and sealing.
6. Install the new knock sensor hand-tight, then torque to manufacturer specifications (typically 12–18 ft-lbs).
7. Reconnect the electrical connector until it clicks into place.
8. Reconnect the battery and clear any stored engine codes if necessary.
9. Start the engine and verify normal operation with no warning lights.

Troubleshooting & FAQ

How do I know if my knock sensor is failing?

Common symptoms include engine pinging or knocking under load, reduced fuel economy, poor acceleration, check engine light illumination, and stored diagnostic trouble codes related to knock sensor circuit or performance.

Will this fit my Volvo Penta sterndrive?

This sensor fits Volvo Penta sterndrive engines that originally used part number 3854905. Verify your engine's part number against the compatibility table to confirm fitment before ordering.

Can I install this myself or do I need a mechanic?

Installation is straightforward for those with basic mechanical skills and proper tools. However, proper torque specifications and electrical connector handling are critical. Professional installation is recommended if you're unfamiliar with marine engine components.

What torque specification should I use?

Typical torque for knock sensors is 12–18 ft-lbs, but always consult your engine's service manual for exact specifications. Over-tightening can damage the sensor or mounting threads.

How often should the knock sensor be replaced?

Knock sensors typically last many years under normal conditions. Replace when you experience knock-related engine codes, audible engine knock, or performance issues. Routine replacement is not usually required unless failure symptoms appear.

What's the difference between this and the OEM sensor?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

How fast will this ship and what does it cost?

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

What warranty and return options are available?

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

• Verify images/specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.