Oshkosh Cummins DEF Head Unit
OSHKOSH CUMMINS 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-FA01-12 ( OEM Part Number 4202057 ). This part is primarily made for a Cummins , 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 | 4202057 |
| Additional OEM | 4202057 |
ADDITIONAL DETAILS
| CONDITION | Remanufactured |
| UPC / Barcode | 00840490540309 |
| 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.
Reliable DEF system management is provided by the Oshkosh Cummins DEF Head Unit: OEM 4202057, a direct-fit component for compatible Oshkosh vehicles and equipment. Built to OEM standards, this unit monitors diesel exhaust fluid level, temperature, and quality to maintain emissions compliance and consistent aftertreatment operation. Its durable construction is designed for long-term service in demanding environments, protecting both the exhaust system and overall engine efficiency. By choosing an OEM DEF head unit, you minimize compatibility risks and ensure dependable reliability. This component is a trusted solution for keeping Oshkosh Cummins-powered machinery operating smoothly and without interruption.
PEOPLE ALSO ASKS | BLOG(S)
The DEF Head Unit, OEM number 4202057, is a multifunction module used in certain Oshkosh vehicles powered by Cummins engines. It’s mounted atop the Diesel Exhaust Fluid (DEF) tank, and it integrates sensors and fluid routing components necessary for maintaining proper emissions control via the SCR (Selective Catalytic Reduction) system.
The primary purpose of the 4202057 DEF Head Unit is to monitor and manage the DEF fluid so your engine’s emissions system works correctly. Key responsibilities include:
- Sensing how much DEF fluid remains in the tank and feeding that information to the engine’s control system.
- Tracking DEF fluid temperature to ensure it’s in the correct operational range (because DEF can freeze or degrade when too cold or too warm).
- Filtering the fluid (in this model, with a ~40‑micron mesh) to eliminate contaminants before the fluid moves to the dosing or injection system.
- Managing both suction (drawing DEF from the tank) and return flow to ensure reliable fluid delivery without air pockets or flow disruptions.
Without a properly functioning head unit like OEM 4202057:
- The engine may display warning codes or go into derate mode (losing power) due to DEF system faults.
- Emissions may increase and the SCR system may fail to reduce NOₓ emissions effectively.
- Downstream components (like the DEF injector or SCR catalyst) may suffer if contaminated or mismanaged DEF is used.
- You could risk non‑compliance with emissions regulations, more frequent maintenance, or unexpected downtime.
Maintaining or replacing the 4202057 head unit ensures your DEF system stays healthy, making sure your Oshkosh vehicle runs cleanly, reliably, and within regulatory requirements.
The DEF (Diesel Exhaust Fluid) head unit is a key part of your vehicle’s aftertreatment system. It measures DEF level, temperature, and quality, then sends that information to the engine control module (ECM). If it fails, the system may receive false data — and that can create major problems for your vehicle.
What Can Go Wrong When the DEF Head Unit Fails?
A failing or failed DEF head unit may cause:
- Incorrect DEF level readings
- The dashboard may show the tank as empty or full, regardless of reality
- False system warnings
- “Service DEF System” or “Incorrect DEF Quality” may appear, even if fluid is fresh
- Unexpected derate
- The engine may reduce speed or limit throttle due to assumed system faults
- Failed emissions test
- Inaccurate readings may trigger codes that cause a test failure
- Check engine light
- The ECM may store fault codes that affect overall drivability
If the DEF head unit fails, it typically cannot be repaired — it must be replaced. A proper diagnosis using a scan tool and visual inspection will confirm whether it’s the root cause.
Yes, a faulty unit can trigger derates, power loss, and downtime.
Match your existing unit’s part number with OEM 4202057 before replacement.
Yes, it is built to handle harsh conditions typical of Oshkosh equipment operations.
Cummins DEF Head Units
