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Thomas Bus Cummins ISB 6.7L, ISL, L9 DEF Head Unit

THOMAS BUS CUMMINS ISB 6.7L, ISL, L9 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 NUMBER04-35649-002
PART TYPEDEF Head Unit
BRANDTamerx Diesel Products
ENGINE MAKECummins
ENGINE TYPEISB 6.7L, ISL, L9
YEAR2018-2024
PART NUMBER2324-18-1
APPLICATION NOTESThomas Bus
ADDITIONAL NOTESDEF Header, Conc, 6-Bolt, Cummins, 18"

PRODUCT DESCRIPTION

This is a Remanufactured, Tamerx DEF Head Unit, Tamerx part number 2324-18-1 ( OEM Part Number 04-35649-002 ).This part is primarily made for a Cummins ISB 6.7L, ISL, L9, production years 2018-2024, and comes with a One Million Miles or One Year Warranty. For additional warranty info Click Here

Additional Notes: DEF Header, Conc, 6-Bolt, Cummins, 18"

OEM NUMBERS

Primary OEM04-35649-002
Additional OEM04-31354-000, 04-31354-001, 04-31354-002, 04-31354-003, 04-31354-004, 04-35649-002

ADDITIONAL DETAILS

CONDITIONRemanufactured
UPC / Barcode00840490541610
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.


Elevate your transit emissions game with the Thomas Bus Cummins ISB 6.7L / ISL / L9 DEF Head Unit — precision-engineered to deliver real-time monitoring of DEF level, temperature, and quality across your SCR system. Rugged and reliable, this OEM-grade module integrates seamlessly with your engine electronics to help prevent derates and keep your buses running clean, smooth, and compliant on every route.

FITMENT CHART

YEARMAKEENGINE(S)
2018Cummins ISB 6.7L ISL L9
2019Cummins ISB 6.7L ISL L9
2020Cummins ISB 6.7L ISL L9
2021Cummins ISB 6.7L ISL L9
2022Cummins ISB 6.7L ISL L9
2023Cummins ISB 6.7L ISL L9
2024Cummins ISB 6.7L ISL L9

PEOPLE ALSO ASKS | BLOG(S)

For operators of Thomas school buses powered by Cummins ISB 6.7L, ISL, or L9 engines, emission system reliability is a critical priority. The DEF (Diesel Exhaust Fluid) head unit is one of the unsung heroes in that system. It ensures the engine control unit (ECU) receives accurate data on fluid level, temperature, and urea concentration—without which your SCR (Selective Catalytic Reduction) system can’t function properly. A failing DEF head can trigger warning codes, force derates, or even lockouts during critical operations.

  • Monitors DEF fluid properties (level, temperature, urea concentration) and sends real-time data to the ECU

  • Regulates precise dosing of DEF into the exhaust stream to enable correct NOx reduction via the SCR system

  • Built to match OEM tolerances for Thomas Bus / Cummins ISB, ISL, L9 platforms, ensuring plug-and-play compatibility

  • Helps prevent fault codes, emissions warnings, or engine derates stemming from sensor drift or inaccurate data

  • Designed to withstand vibration, thermal cycling, and exposure to DEF’s corrosive chemistry

  • Allows for field replacement to minimize downtime and keep buses running reliably

In the world of transit and school bus service, every minute out of commission costs money and impacts safety. Equipping your fleet with properly functioning DEF head units ensures your emissions control remains precise, compliant, and dependable. Don’t let a degraded sensor compromise your system—make your DEF head unit a maintenance priority.

The DEF (Diesel Exhaust Fluid) head unit is vital to keeping your vehicle’s emissions system in check. It measures fluid level, quality, and temperature, sending that information to the engine control module (ECM). If it malfunctions, you might still be able to drive, but doing so comes with significant risks that can quickly lead to reduced performance or even shutdown.

What Happens If You Keep Driving

  • Dashboard Warnings
    Check engine lights or DEF alerts may appear as soon as the head unit starts failing.

  • False or Inaccurate Readings
    The system may show low, empty, or poor-quality DEF, even when the fluid is fine.

  • Diagnostic Trouble Codes (DTCs)
    Fault codes such as P203F, P205B, or P207F may be triggered, indicating sensor issues.

  • Reduced Engine Power (Derate Mode)
    If the ECM cannot confirm DEF data, it may cut engine power or limit speed to stay compliant.

  • Possible Shutdown
    Continued operation without fixing the issue can result in stricter limits or complete vehicle shutdown.

While it’s technically possible to drive with a malfunctioning DEF head unit, it’s not advisable. What starts as a warning light can quickly escalate into derate mode or shutdown, leading to downtime and expensive repairs. Addressing the issue promptly is the best way to keep your vehicle reliable, compliant, and on the road.

Depressurize the DEF system, disconnect wiring harnesses, unbolt the unit, and reseal properly when reinstalled.

With proper care, clean DEF, and functional sensors/heaters, it can last for many years alongside the emissions system.

Use a diagnostic tool to view live DEF level and temperature readings and confirm no active fault codes.

Use high-purity ISO-compliant DEF, avoid contamination, inspect liquid strainer regularly, and verify sensor and heater function.

 

Cummins DEF Head Units

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