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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →EPA did not issue one universal, owner-installed fix for diesel exhaust fluid (DEF) power-loss problems. On August 12, 2025, Administrator Lee Zeldin announced guidance urging manufacturers to update software on existing diesel vehicles and equipment so operators have more time to address DEF-related faults before power is reduced. Whether an update is available—and what it changes—depends on the manufacturer and engine. EPA later issued separate guidance on DEF sensors and access to repair information.
Why a DEF fault can reduce engine power
Most on-road diesel trucks and many nonroad machines have used selective catalytic reduction (SCR) systems since 2010, according to EPA’s overview of DEF. SCR injects DEF into the exhaust to reduce nitrogen oxides (NOx). On-board diagnostics monitor the system; low fluid, a fluid-quality issue, suspected tampering, a sensor fault, or another system failure can trigger warnings and an inducement that limits engine performance.
EPA says older strategies could leave some vehicles operating as slowly as five miles per hour. That is EPA’s description of the possible effect of a DEF-related fault, not a measured estimate of how often it happens. DEF is a required part of emissions control on equipment designed to use SCR; adding fresh fluid will not fix a failed sensor, software issue, or other system fault.
What EPA announced, and when
| Date | Action | What it means for owners |
|---|---|---|
| August 12, 2025 | Manufacturer software and inducement guidance | EPA urged manufacturers to revise software on existing vehicles and equipment to give operators more time to repair faults. This is voluntary guidance for in-use equipment, not confirmation that every model has an update. |
| February 3, 2026 | Request for manufacturer data | EPA requested warranty claims, failure rates, and repair information from 14 major on-road and nonroad manufacturers for model years 2016, 2019, and 2023. EPA said the companies accounted for over 80% of products used in DEF systems and had 30 days to respond. The request was intended to inform next steps; it was not a completed independent failure analysis. |
| March 27, 2026 | Sensor guidance | EPA clarified that manufacturers may remove traditional urea-quality sensors and use NOx sensors under existing regulations, and that approved NOx-sensor software updates may be installed on existing engines without being treated as illegal tampering. This does not mean all engines have been converted or can be retrofitted. |
| July 1, 2026 | Repair-access guidance | EPA said manufacturers must provide service and repair information, training, and tools made available to branded service centers, including for DEF systems, on reasonable terms. It also said equivalent generic parts may be used, while noting that the Clean Air Act does not guarantee warranty relief when a consumer chooses a noncertified part. |
| July 9, 2026 | Proposed heavy-duty rule revision | EPA announced a proposal to revise heavy-duty compliance requirements. A proposal is not a final regulation, and any savings depend on finalization. |
EPA’s February 2026 data request covered 14 manufacturers; by its March 27 sensor announcement, EPA said it had received data from 11 of them and would publish a complete assessment after receiving all submissions. The March release also cited a projected $13.79 billion per year in savings, attributing that estimate to the U.S. Small Business Administration. It is a projection, not a reported realized saving.
#1 Best Overall
- One gallon of is used approximately every 300 miles
- A truck with a 20 gallon DEF tank can go up to 6000 miles between fill-ups
- When used in an SCR system will reduce the levels of NOx emissions of those engines
- Fit type: Universal
What the August 2025 guidance says about inducements
EPA’s August announcement set out separate details for new on-road trucks and nonroad equipment. It said new model-year 2027 diesel on-road trucks must be engineered to avoid sudden, severe power loss after running out of DEF. That statement concerns new on-road trucks; it is not a blanket rule for every existing truck, tractor, or engine.
Nonroad equipment stages described by EPA
| Stage in EPA’s announcement | Timing or condition | Inducement described |
|---|---|---|
| Before | Four hours | Idle only |
| Initial | After 36 hours | 25% torque reduction |
| Final | After 100 hours | 50% torque reduction |
These figures are EPA’s description of the nonroad equipment stages in its August 12, 2025 announcement, not a universal schedule for every diesel engine. EPA said constant-speed nonroad engines and generator sets do not receive the initial inducement step because torque reduction could limit their function. For nonroad equipment after inducement, EPA described three restarts at full power, for up to 30 minutes each.
Rank #2
- One gallon of is used approximately every 300 miles
- A truck with a 20 gallon DEF tank can go up to 6000 miles between fill-ups
- When used in an SCR system will reduce the levels of NOx emissions of those engines
Does the guidance apply to your truck or tractor?
Not automatically. EPA’s overview describes the field changes for in-use equipment as voluntary manufacturer guidance, and software availability varies by manufacturer and engine. The announcements do not establish that a particular update or repair is available for every model, or that a single software change applies across an entire make or model year.
- Identify the equipment’s make, model, model year, and engine family. For a truck, have the VIN available when contacting a dealer.
- Ask the manufacturer or an authorized dealer whether an EPA-related DEF software update or approved sensor update applies to that specific engine, and whether it has been installed.
- If a DEF warning or inducement is active, ask for the diagnostic trouble codes and the recommended repair. Do not assume that topping up DEF or updating software resolves a hardware fault.
- If considering an independent repair shop or a generic part, confirm that the shop has compatible service information, tools, and training. Check the part’s certification and the effect on warranty coverage before authorizing work.
What the sensor and repair guidance changes—and what it does not
EPA’s March 2026 sensor guidance addresses which sensor arrangements manufacturers may use and says approved NOx-sensor software updates for existing engines need not be treated as illegal tampering. EPA reported that preliminary review suggested DEF sensor failures were a significant source of warranty claims and DEF-related inducements. That is an agency statement about preliminary warranty data, not proof that a sensor is the cause of every DEF fault.
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- Meets GM Original Equipment specifications to be approved for use in GM vehicles as well as in non-GM diesel vehicles that have an SCR (Selective Catalytic Reduction) system to meet regulated NOx emissions (Based on EPA certification testing. Your actual emissions will vary based on several factors including temperature, terrain, and driving conditions).
- High quality formula is made from high purity urea and deionized water.
- Meets API regulations and ISO 22241 standard for purity and concentration
- Nozzles sold separately
The July repair-access guidance concerns access to service information, training, and tools that manufacturers provide branded service centers. It does not confirm that a specific update, part, or repair is available for a particular engine. Nor does it promise warranty coverage for every repair choice: EPA specifically noted that using a noncertified part does not guarantee relief under the Clean Air Act.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is this an emissions-system bypass?
No. EPA describes the 2025 software guidance and 2026 sensor guidance as ways to reduce disruptive inducements while retaining emissions standards. They are not permission to disable SCR, remove required emissions controls, or defeat diagnostics. An emissions-system bypass is different from a manufacturer-approved software or sensor change.
Quick Recap
Best Value
- ENGINEERED: For use in Selective Catalytic Reduction (SCR) systems on diesel engines
- EFFICIENCY: BlueDEF diesel exhaust fluid is key to helping improve fuel economy by up to five percent
- PROTECTION: Diesel exhaust fluid is non-toxic and safe to handle
- QUALITY: Stable, colorless and odorless, and also meets ISO Standards 22241 for purity and composition
- EFFORTLESS: Easily Inject the fluid into your exhaust stream with a specialized dosing module
Rank #4
- Blue Def DEF002-2PK Diesel Exhaust Fluid, 2.5 Gallon, 2 Pack
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