Newmar Cummins ISX DEF Head Unit
NEWMAR CUMMINS ISX 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 4310-18-11 ( OEM Part Number 31736 ). This part is primarily made for a Cummins ISX, 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 | 31736 |
| Additional OEM | 31736 |
ADDITIONAL DETAILS
| CONDITION | Remanufactured |
| UPC / Barcode | 00840490540453 |
| 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.
Designed for Newmar motorcoaches powered by Cummins ISX engines, the DEF Head Unit OEM 31736 provides precise Diesel Exhaust Fluid system management and dependable emissions control. This genuine OEM component is built to Cummins specifications, ensuring accurate fitment, consistent DEF flow, and reliable system monitoring. By maintaining proper DEF operation, it supports emissions compliance and helps ensure smooth, efficient engine performance during long-distance travel. Its durable construction is engineered to withstand the demands of continuous use, offering long service life and dependable reliability. For RV owners and service professionals, this DEF head unit delivers OEM-certified quality and the assurance of consistent performance for every journey.
PEOPLE ALSO ASKS | BLOG(S)
The DEF (Diesel Exhaust Fluid) Head Unit with OEM number 31736 is a specialized component used in Newmar motorhomes or coaches that use Cummins ISX engines. It is mounted on the DEF tank and serves several essential roles within the vehicle’s emissions / aftertreatment system.
Core Uses & Functions
- Monitoring DEF Level
- The head unit senses how much Diesel Exhaust Fluid is in the tank and sends that information to the engine control system. This ensures the system knows when the DEF level is low and needs refilling.
- Temperature Sensing
- It tracks the temperature of the DEF fluid. If the fluid is too cold (risking freezing) or unusually warm, the system can adjust or alert the operator.
- Fluid Routing / Distribution
- As a header, the unit provides the path for pulling DEF from the tank into the dosing/injection system (pickup port) and often supports a return path for unused fluid.
- Filtration and Clean Delivery
- A built-in filter or strainer helps prevent particles, crystals, or contaminants from entering fragile downstream components like the dosing injector.
- Signal & Feedback to Control Systems
- The sensors inside the head unit relay readings (level, temperature, etc.) to the engine control module (ECM) or emission control module. That feedback allows the system to manage DEF dosing, initiate regeneration, or trigger warnings / fault codes.
OEM 31736 is the “brains and plumbing” in Newmar’s ISX DEF tank. It ensures the engine’s SCR system knows how much DEF is available, whether it’s in usable condition, delivers it cleanly, and communicates everything needed to manage emission control effectively.
The DEF (Diesel Exhaust Fluid) Head Unit is a vital part of your truck’s emissions system. It monitors the DEF level, temperature, and quality, sending critical data to the Engine Control Module (ECM). When the unit begins to fail, your vehicle may display warnings or even enter derate mode. Knowing how to properly diagnose a bad DEF Head Unit can save you from unnecessary downtime and repair costs.
Common Symptoms of a Failing DEF Head Unit
Before performing a full diagnosis, look for these warning signs:
- DEF system fault codes or emissions warnings on the dashboard
- Check engine light related to DEF or emissions errors
- Incorrect DEF readings, such as showing empty when the tank is full
- Premature derate countdowns, restricting vehicle speed or power
- Inconsistent or fluctuating DEF readings on your display
Step-by-Step: How to Diagnose a Bad DEF Head Unit
- Inspect the DEF Tank
- Check for contamination, debris, or crystallization inside the tank. Buildup around the sensors can cause inaccurate readings that mimic Head Unit failure.
- Check Electrical Connections
- Inspect the wiring harness and connectors for corrosion, loose pins, or broken wires. Many “sensor failures” are actually electrical faults.
- Scan for Diagnostic Trouble Codes (DTCs)
- Use a scan tool to look for codes such as P203B, P205B, or P207F — all of which can indicate problems with the DEF Head Unit or its sensors.
- Compare Sensor Readings
- If your diagnostic tool shows temperature, quality, or level readings that don’t match actual DEF conditions, the Head Unit is likely failing.
- Verify Power and Ground Signals
- Using a multimeter, confirm that the Head Unit is receiving proper voltage and ground from the vehicle’s harness. Faulty power supply can cause intermittent operation.
If your tests confirm inaccurate readings, communication faults, or internal sensor errors, replacement is the only reliable fix. The DEF Head Unit is a sealed component — it cannot be cleaned, repaired, or recalibrated once damaged.
Diagnosing a bad DEF Head Unit involves a mix of visual inspection, electrical testing, and code scanning. If readings remain inconsistent or fault codes persist after verifying wiring and fluid quality, replacing the Head Unit is the safest and most effective way to restore your emissions system’s performance.
Yes, freezing or overheating can harm the internal sensors or electrical connectors.
Many versions include an integrated heater to prevent DEF from freezing in low temperatures.
Common causes include DEF contamination, wiring corrosion, or prolonged exposure to harsh conditions.
The system may record fault codes and enter derate mode until the issue is resolved.
Cummins DEF Head Units
