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Tiffin Motorhomes Cummins X12 DEF Head Unit

TIFFIN MOTORHOMES CUMMINS X12 DEF HEAD UNIT

Shipping ICON

ORDERS PLACED BEFORE 3PM EST WILL SHIP SAME DAY

WARRANTY ICON

WARRANTY
1M MILES OR 1 YEAR

$895.00

CORE CHARGE:

$250.00
iCORE DISCLAIMER: The CORE charge is a 30 day hold and will not be processed as long as the CORE is returned within 30 days. If you do not have a CORE or fail to return the CORE within 30 days, the CORE charge hold amount will be processed at that time.

AVAILABILITY IN STOCK
OEM NUMBER
PART TYPEDEF Head Unit
BRANDTamerx Diesel Products
ENGINE MAKECummins
ENGINE TYPEX12
YEAR
PART NUMBER4310-18-39
APPLICATION NOTESTiffin Motorhomes
ADDITIONAL NOTESDEF Header, 40 MICRON, 18"

PRODUCT DESCRIPTION

This is a Remanufactured, Tamerx DEF Head Unit, Tamerx part number 4310-18-39. This part is primarily made for a Cummins X12, and comes with a One Million Miles or One Year Warranty. For additional warranty info Click Here

Additional Notes: DEF Header, 40 MICRON, 18"

OEM NUMBERS

ADDITIONAL DETAILS

CONDITIONRemanufactured
UPC / Barcode00840490541511
WEIGHT8.00 LBS

SHIPPING OPTIONS

Ship Weight : 8.00 LBS
UPS Ground, 2nd Day Air, Next Day Air

SHIPPING POLICY

Tamerx Diesel Products ships via UPS Ground. Next day air shipping can be arranged for a reasonable price of anywhere from $50.00 - $100.00 depending on the weight of the product and your location. We will do everything we can to make sure that you get the service you need. We understand how important it is to receive your order as quickly as possible.
In most cases Tamerx Diesel Products only needs one address, as long as your product is shipping to the same location as your billing information. In order to eliminate credit card fraud, your billing information must match the credit card you provide.

The terms, conditions, and details of our warranty vary from product to product. Specific warranty details can be found below.

Tamerx Diesel Products provides a replacement warranty on all of our parts. The duration and mileage limitations of the warranty vary by product and are specified on the product's detail page/item listing.

Please note that the warranty covers replacement of the part and the cost of shipping the replacement part to you only. It does not cover any shop, labor, towing, or any similar or related costs. This is not a "money back guarantee".

If you experience a problem with your part or it is not functioning properly, the correct warranty procedure is to call us at (510) 257-1777 (8:00 AM - 5:00 PM ET Monday through Friday). Be sure to have your order number and/or other relevant order information ready so we can easily locate your order and resolve your issue as quickly as possible. From that point, we will review with you any troubleshooting steps that may need to be taken and other areas or systems that can be checked to rule out external problems contributing to your part's issue. If a replacement is determined to be necessary, we will then arrange for your replacement part to ship out ASAP and issue any necessary return shipping labels and/or documents.

As is the case for the majority of the diesel products sold on Tamerx Diesel Products, your part's warranty is active as soon as you install it. In some other cases, warranty activation is contingent upon you sending us your core (i.e., your old part). Tamerx Diesel Products will provide you a return shipping label for parts that have a warranty with a core return condition. When we have received your core return, the part's warranty coverage begins. We reserve the right to void the product warranty if your core is not received within the allotted time, or if it isn't received at all. If the warranty for the diesel part you are purchasing has a core return requirement, it will be clearly noted on the product detail page/item listing.

What is a Core Charge?

A core charge (also called "core deposit") is similar to the deposit you might pay for a can or bottle of soda and is a standard requirement in the auto parts industry. For example, in many states, to promote recycling, you pay a deposit when you purchase a can of soda and receive your deposit back when you return the empty can. Many automotive parts have a core charge, or core price, that works in essentially the same way as a soda can deposit.

30 Day Core Charge Hold

You authorize Tamerx Diesel Products, to hold your credit card for the specified core charge amount and that you agree to return your core with 30 days of receiving the purchased part. When we have received your core return, the hold is released and the core charge payment is canceled.

The customer, or parts buyer, is responsible for any shipping costs associated with core returns unless otherwise specified in the product listing/detail page. Tamerx Diesel Products offers prepaid UPS shipping labels (SKU numbers UPS-CR1 and UPS-CR2) for use in returning your core that are available for purchase on our website during your shopping/order process.

The shipping label you will need to use for the core return is dependent upon what part you are purchasing. UPS-CR1 is good for cores weighing up to 20 pounds. UPS-CR2 is appropriate for shipping cores weighing 21 pounds or more. You must include enough information with the core return that clearly identifies it as a.) a Core Return, and b.) contains enough information we can use to clearly associate the core return with your order. Including a copy of the invoice or packing slip that came with the original shipment, clearly marked "Core Return", is ideal. Alternately, you can include a note marked as "Core Return" that includes your order number, full name and address, and phone number or other contact information. Failure to include this information with your returned core will most likely delay any due core credit being issued and/or delay any applicable warranty activation. Core returns need to be for the exact part purchased and cannot be damaged. Substituting another part in place of the part you have purchased is not acceptable.

All fluids must be drained.

If you have purchased a set or a parts package, you will need to return cores for all components of the set. For example, if you have purchaed a high pressure oil pump with an IPR valve, you will need to return both HPOP and IPR valve cores to receive proper credit. If you have purchased an EGR cooler/EGR valve package, your core return must consist of an EGR cooler core and an EGR valve core, or core credit will not be given.

Core Charges are often mandated by state legislature, and, as such, the actual core charge and taxes on the charge may vary depending on the state in which you buy your part. The Tamerx Diesel Products core charge presented to you online today with your item is representative of the most common core charge.


Keep your road adventures clean and compliant with the Tiffin Motorhomes Cummins X12 DEF Head Unit — precision built to monitor DEF level, temperature, and quality in real time. Rugged and reliable, it integrates seamlessly with your SCR system to help eliminate derates and ensure emissions performance mile after mile. Backed by Tamerx’s trusted warranty, this unit is the upgrade your motorhome deserves.

PEOPLE ALSO ASKS | BLOG(S)

Driving a motorhome powered by the Cummins X12 is all about combining performance, efficiency, and emissions compliance. One of the least obvious—but absolutely critical—components making that possible is the DEF (Diesel Exhaust Fluid) Head Unit. For Tiffin Motorhomes running the X12 engine, the OEM 4310-18-39 DEF head ensures your system can accurately measure fluid properties, dose urea, and communicate with your ECU. When it fails or drifts, you face error codes, derates, or emissions faults—and none of those make for a restful road trip.

  • Monitors DEF fluid level, temperature, and urea concentration, relaying precise feedback to your engine controller

  • Ensures precise urea dosing into the exhaust stream so the SCR (Selective Catalytic Reduction) system can reduce NOx emissions effectively

  • Manufactured to match OEM 4310-18-39 tolerances, making it a drop-in replacement with correct calibration

  • Helps prevent emissions warnings, fault codes, or engine derates triggered by sensor drift or failure

  • Built to endure rigors of road use—vibration, temperature swings, and the chemical stress of DEF fluid

  • Offers field-friendly installation to minimize downtime on your motorhome

Many motorhome owners push off DEF head maintenance until a warning light appears. But by that time, you may already be locked into reduced power or regulatory fault codes. Installing the correct OEM 4310-18-39 Tiffin Cummins X12 DEF Head Unit restores the integrity of your emissions feedback loop, protects your SCR system, and helps ensure your journey stays smooth, clean, and worry-free. When your rig demands reliability, this is one part you can’t afford to skip.

The DEF (Diesel Exhaust Fluid) head unit is an essential part of a diesel engine’s emissions system, monitoring fluid level, quality, and temperature. Like any electronic component, it has a limited lifespan. Understanding how long it typically lasts—and what factors affect its durability—can help operators plan maintenance and reduce costly downtime.

Factors That Affect DEF Head Unit Lifespan

  • Average Lifespan
    Most DEF head units last 5 to 7 years under normal operating conditions.

  • Vehicle Usage
    High-mileage trucks or equipment that run daily often experience shorter lifespans compared to light-use vehicles.

  • Environmental Exposure
    Extreme heat, freezing temperatures, and frequent outdoor storage can accelerate wear and reduce service life.

  • DEF Fluid Quality
    Using only clean, ISO-compliant DEF protects sensors from contamination and helps extend the unit’s life.

  • Maintenance Habits
    Regular inspections, cleaning, and careful handling during service play a big role in maximizing durability.

  • Warning Signs of Aging
    Inaccurate DEF readings, recurring fault codes, or false alerts may indicate the unit is nearing the end of its life.

While a DEF head unit is designed to last several years, its actual lifespan depends on usage, environment, and maintenance. By using high-quality DEF, protecting the system from extreme conditions, and staying proactive with inspections, operators can extend its service life and keep their vehicles compliant and reliable.

You might see DEF system warnings, inconsistent level/temperature readings, or engine derate.

It should be checked during routine emissions or DEF system maintenance or upon seeing error codes.

Flush the DEF fluid pickup area with clean, certified DEF and gently clean or replace the internal filter element.

Yes, contaminated or impure DEF can clog the strainer, damage sensors, and lead to failure.

Cummins DEF Head Units

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