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Terex Cummins ISL DEF Head Unit

TEREX CUMMINS ISL 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 NUMBER66900101
PART TYPEDEF Head Unit
BRANDTamerx Diesel Products
ENGINE MAKECummins
ENGINE TYPEISL
YEAR
PART NUMBER4310-18-38
APPLICATION NOTESTerex
ADDITIONAL NOTESDEF Header, 40 MICRON, 18"

PRODUCT DESCRIPTION

This is a Remanufactured, Tamerx DEF Head Unit, Tamerx part number 4310-18-38 ( OEM Part Number 66900101 ). This part is primarily made for a Cummins ISL, 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

Primary OEM66900101
Additional OEM66900101

ADDITIONAL DETAILS

CONDITIONRemanufactured
UPC / Barcode00840490541504
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.


Power your performance with the Terex Cummins ISL DEF Head Unit — precision-engineered to deliver real-time tracking of DEF fluid level, temperature, and quality. Built rugged and tested to match OEM reliability, this head unit integrates seamlessly with ISL systems to help prevent derates and keep your equipment compliant. Built for tough environments and backed by Tamerx’s proven warranty, it’s the emissions upgrade that works as hard as you do.

PEOPLE ALSO ASKS | BLOG(S)

When your Terex equipment runs a Cummins ISL engine, the DEF (Diesel Exhaust Fluid) head unit might be one of the least visible parts—but it’s one of the most critical. The Terex Cummins ISL DEF Head Unit (OEM 66901701) ensures your aftertreatment system knows exactly how much DEF is in the tank, what its temperature is, and how concentrated it is. A failing or inaccurate DEF head can lead to warning lights, emission faults, or engine derates just when you can’t afford them.

  • Continuously measures DEF fluid level, temperature, and urea concentration and relays that information to the engine control module

  • Controls precise dosing of urea into the exhaust stream, enabling the SCR (Selective Catalytic Reduction) system to reduce NOx reliably

  • Designed to meet OEM 66901701 specifications, allowing for proper fit and calibration on Terex / Cummins ISL setups

  • Helps prevent fault codes, emission warnings, and power derates that often arise from sensor drift or failure

  • Built to withstand tough operating conditions—vibration, wide temperature swings, and exposure to DEF’s chemical properties

  • Relatively easy to replace, minimizing downtime and restoring your emissions system integrity

If your equipment is showing DEF system errors or SCR faults, your DEF head is often the first place to look. Replacing it with the correct OEM 66901701 unit restores reliable feedback, protects your emissions chain, and ensures your machine stays compliant under all conditions. When emissions matter, this head unit is one component you can’t afford to ignore.

The DEF (Diesel Exhaust Fluid) head unit is a critical part of your vehicle’s emissions system, monitoring fluid level, quality, and temperature. When it malfunctions, the system may provide incorrect data to the engine control module (ECM). While the vehicle may still start and run, driving with a faulty DEF head unit can quickly lead to bigger problems.

What to Expect if You Drive With a Malfunctioning DEF Head Unit

  • Warning Lights and Alerts
    The check engine light or DEF system alerts may appear on the dashboard as soon as the unit begins failing.

  • False or Inaccurate Readings
    A malfunctioning head unit may report incorrect DEF levels or quality, making it hard to track actual system status.

  • Risk of Derate Mode
    If the ECM cannot verify DEF data, it may reduce engine power or limit vehicle speed to maintain emissions compliance.

  • Potential Shutdown
    Continued operation without resolving the issue may trigger stricter emissions protocols, eventually leading to vehicle shutdown.

  • Compliance and Reliability Issues
    Driving with a malfunctioning DEF head unit risks violating emissions standards and increases the chance of unexpected downtime.

Yes, you can technically drive with a malfunctioning DEF head unit—but it’s not advisable. What begins as a simple warning can escalate into derate mode or even shutdown, leaving you stranded and facing costly repairs. Addressing the issue promptly is the best way to keep your vehicle reliable, compliant, and on the road.

Symptoms include erratic or missing readings, DEF system warning codes, or engine derate condition.

The engine control may believe the system has too little or too much DEF and trigger warnings or limit performance.

It should be inspected during regular maintenance or whenever DEF or emissions warnings appear.

Flush the DEF pickup area with clean, compliant fluid, and clean or replace the internal strainer when clogged.

Cummins DEF Head Units

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