Mercury Optimax ECU ECM | Part Number 856496A9 | Fits 1998–1999 Mercury Optimax 150HP 2.5L DFI V6 | New OEM | 1-Year Warranty

Product Overview

Maintain the performance and reliability of your Mercury Optimax outboard with this genuine Mercury Optimax Engine Control Unit (ECU/ECM), Part Number 856496A9. Designed for select 1998–1999 Mercury Optimax 150HP 2.5L V6 Direct Fuel Injection (DFI) outboard engines, this OEM control module manages critical engine functions, including fuel injection, ignition timing, and overall engine operation. This unit is brand new and has never been installed, making it an ideal replacement for a damaged or malfunctioning ECU. It features the factory A9 calibration, specifically engineered for the 150HP Optimax application, and includes untouched factory connectors and pins for straightforward installation. Backed by a 1-Year Warranty, this genuine Mercury ECU offers dependable performance and long-term peace of mind.

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Key Features

• Genuine OEM Mercury Optimax ECU
• OEM Part Number: 856496A9
• Brand New – Never Installed
• Factory A9 Calibration for 150HP Models
• Original Factory Connectors and Pins
• Direct OEM Replacement
• Ready for Installation
• 1-Year Warranty Included

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Technical Specifications

Specification	Details
Brand	Mercury
Product Type	Engine Control Unit (ECU/ECM)
Condition	New
OEM Part Number	856496A9
Engine Type	Optimax 2.5L V6 Direct Fuel Injection (DFI)
Horsepower	150 HP
Model Years	1998–1999

Compatible OEM Part Numbers

Chain Numbers

• 856496R9
• 857127A4
• 858891A21

Also Replaces

• 85448717
• 85448721
• 85448726

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Compatible Applications

Designed for select Mercury Optimax outboard engines including: Model Years

• 1998
• 1999

Engine

• 2.5L V6 Direct Fuel Injection (DFI)

Horsepower

• 150 HP

Important Calibration Note The 1998 Optimax 135HP and 150HP engines use the same ECU family, but the calibration suffix is different.

• A8 Calibration = 135 HP
• A9 Calibration = 150 HP

Always match the calibration suffix on your existing ECU before ordering to ensure proper compatibility.

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Condition

This is a brand-new genuine Mercury OEM ECU.

• Never installed
• Factory connectors and terminals untouched
• Original A9 calibration for 150HP applications
• Ready for installation

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What's Included

Your purchase includes:

• Mercury Optimax Engine Control Unit (ECU/ECM)
• OEM Part Number 856496A9

No wiring harnesses, sensors, mounting hardware, or additional electronic components are included unless shown in the product photos.

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Shipping Information

Every ECU is carefully packaged to protect sensitive electronic components during transit. We offer secure shipping throughout the United States, with international shipping available upon request. For an accurate shipping quote, please provide:

• Country
• ZIP or Postal Code
• Commercial or Residential Address

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Warranty

This Mercury Optimax ECU is backed by a 1-Year Warranty. If the unit experiences a covered failure during normal operation within the warranty period, EZ Boats Marine will repair, replace, or refund the item if a replacement is unavailable, in accordance with our warranty policy.

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Why Buy from EZ Boats Marine?

• Genuine OEM Mercury Marine Parts
• Brand-New Factory Components
• 1-Year Warranty Included
• Secure Packaging
• Fast Nationwide and International Shipping
• Competitive Pricing
• Knowledgeable Customer Support
• Trusted Source for Outboard Motors and Marine Parts

EZ Boats Marine is committed to providing high-quality OEM marine parts backed by dependable service and expert support.

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Frequently Asked Questions

Which engines does this ECU fit?

This ECU fits select 1998–1999 Mercury Optimax 150HP 2.5L V6 DFI outboard engines. Always verify your engine's model number, serial number, and ECU calibration before ordering.

What is the A9 calibration?

The A9 calibration is specifically programmed for 150HP Optimax engines. It should not be substituted for the A8 calibration, which is used on certain 135HP models.

Is this ECU new?

Yes. This is a brand-new genuine Mercury OEM ECU that has never been installed.

Which part numbers does this ECU replace?

This ECU is compatible with or replaces the following part numbers:

• 856496R9
• 857127A4
• 858891A21
• 85448717
• 85448721
• 85448726

Does this ECU include a warranty?

Yes. This ECU is backed by a 1-Year Warranty, providing added confidence with your purchase.