Capacity Cummins ISB 6.7L DEF Head Unit
CAPACITY CUMMINS ISB 6.7L DEF HEAD UNIT
ORDERS PLACED BEFORE 3PM EST WILL SHIP SAME DAY
WARRANTY
1M MILES OR 1 YEAR
PRODUCT DESCRIPTION
This is a Remanufactured, Tamerx DEF Head Unit, Tamerx part number 5410-18-FC01-1 ( OEM Part Number 909934 ). This part is primarily made for a Cummins ISB 6.7L, 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 OEM | 909934 |
| Additional OEM | 909934 |
ADDITIONAL DETAILS
| CONDITION | Remanufactured |
| UPC / Barcode | 00840490540446 |
| WEIGHT | 8.00 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.
Developed for Capacity yard trucks powered by Cummins ISB 6.7L engines, the DEF Head Unit OEM 909934 ensures precise Diesel Exhaust Fluid system operation and reliable emissions control. This genuine OEM component is manufactured to Cummins and Capacity specifications, providing accurate fitment, consistent DEF flow, and dependable system monitoring. By maintaining proper DEF function, it helps support emissions compliance and smooth engine performance in demanding industrial and logistics environments. Built with durability in mind, it withstands harsh operating conditions, offering long-lasting reliability and reduced downtime. For fleet operators and maintenance teams, this DEF head unit delivers OEM-certified quality and trusted performance to keep Capacity equipment running efficiently.
PEOPLE ALSO ASKS | BLOG(S)
The DEF Head Unit OEM 909934 (also called a header or sensor head) is mounted on top of the Diesel Exhaust Fluid (DEF) tank. Its job is to serve as the key interface between the fluid in the tank and the engine’s aftertreatment (SCR) control systems. By sensing, filtering, routing, and communicating, it ensures that DEF is delivered properly when needed.
Core Operation & Workflow
- Sensing DEF Level
- An internal level sensor (a float or probe) monitors how much DEF remains in the tank. That data is updated continuously and sent to the engine control module (ECM). This helps the system know when to warn that DEF is low or when refill is required.
- Monitoring Fluid Temperature
- The head unit includes a temperature sensor to track the fluid’s condition. When temperatures are too low (risk of freezing) or too high, the system can compensate or issue alerts to protect components.
- Routing / Header Function
- The unit includes passages for suction (pickup)—drawing DEF out of the tank toward the dosing or injection system—and return flow—sending unused fluid back into the tank, thereby keeping the lines primed, balanced, and free of air locks.
- Filtration / Protection
- Before the fluid leaves the head unit, it passes through a fine filter (e.g. 40 micron) or strainer. This removes particles, crystals, or contaminants so they don’t damage downstream components like injectors or pumps.
- Signal Communication
- The sensors (level, temperature, sometimes quality) are wired into the head unit’s connector. The sensor outputs—often analog voltages or resistances—are fed to ECM or DEF controller, which uses them to control DEF dosing, regeneration, and fault detection.
- Protective Behavior & Safeguards
- If sensor data indicates abnormal conditions (very low fluid, fluid too cold, contamination), the engine may trigger warnings, limit emission behavior, or enter safe/passive modes to protect the system.
The OEM 909934 head unit is the “control gateway” of the DEF tank. It knows how much fluid is there, ensures it’s usable and clean, delivers it to the dosing system, and provides feedback to the ECM so the SCR system can function correctly. Without it, the engine couldn’t reliably dose DEF, leading to emission errors, possible derates, or damage.
The DEF (Diesel Exhaust Fluid) Head Unit is one of the most important components in your vehicle’s emissions system. It monitors DEF level, temperature, and quality to keep your truck compliant and running efficiently. Because it operates in a harsh environment, proper maintenance is key to extending its lifespan and preventing costly downtime.
Average Lifespan of a DEF Head Unit
Under normal operating conditions, a DEF Head Unit typically lasts 5 to 7 years. However, contamination, temperature extremes, and improper DEF handling can shorten its life dramatically.
Proven Ways to Extend DEF Head Unit Lifespan
- Use Only Certified DEF Fluid
- Always use API-certified DEF fluid that meets ISO 22241 standards. Poor-quality or contaminated DEF can damage sensors and internal components.
- Keep DEF Storage Clean and Sealed
- DEF is sensitive to dirt and moisture. Always store it in sealed, non-metallic containers away from direct sunlight and extreme temperatures.
- Avoid Contamination During Refills
- Use dedicated DEF equipment — never reuse fuel containers or funnels. Even trace amounts of diesel or oil can ruin the DEF system.
- Protect Against Temperature Extremes
- Avoid leaving DEF in freezing or high-heat environments. Freezing causes crystallization, while heat accelerates degradation.
- Perform Regular Inspections
- Check the DEF tank, lines, and connectors for crystals, leaks, or corrosion. Catching small issues early prevents long-term damage.
- Address Fault Codes Promptly
- If you see DEF-related warning lights or fault codes, diagnose them immediately. Ignoring issues can cause the Head Unit to fail prematurely.
With proper care and attention, your DEF Head Unit can last well beyond its expected 5–7 year lifespan. Using clean, certified DEF, maintaining the system regularly, and protecting it from contamination and temperature extremes are the best ways to keep your emissions system reliable and your truck on the road.
It monitors and controls diesel exhaust fluid (DEF) levels and quality in Cummins ISB 6.7L engines used by Capacity trucks.
Common causes include DEF contamination, electrical corrosion, or damage from extreme temperatures.
Yes, frozen DEF can crack the housing or damage internal sensors if not properly heated.
Keep the DEF tank clean and always use certified DEF to prevent sensor contamination.
Cummins DEF Head Units
