|
Thursday,
July 16, 2026 – EPA has proposed substantial changes to
the way diesel engines respond when they
detect low diesel exhaust fluid (DEF),
poor-quality DEF or possible tampering
with selective catalytic reduction (SCR)
systems.
The DEF provisions are part of a much
broader EPA proposal addressing model
year 2027 and later heavy-duty
diesel-engine emissions requirements.
The larger rulemaking would revise
emission-related warranty periods, delay
certain extended useful-life
requirements, authorize nonconformance
penalties for some medium- and
heavy-heavy-duty engines, amend testing
and diagnostic provisions, and revise
requirements for SCR-equipped highway
and nonroad engines. EPA is not
proposing to repeal the underlying model
year 2027 nitrogen-oxide and
particulate-matter standards.
Current SCR systems commonly use
“inducements” or “deratements” —
progressive reductions in engine power
or vehicle speed — to compel operators
to refill the DEF tank or correct an
emissions-system problem. EPA
acknowledges that derates have caused
operational and safety problems for
truckers, farmers, motorcoach operators
and other diesel-equipment users.
Defective sensors, corroded wiring and
diagnostic errors can trigger derates
even when the operator has used proper
DEF and has not tampered with the
system.
Under the Agency’s proposal, original
equipment manufacturers generally would
replace DEF-related engine and speed
derates with visible and audible
warnings. For a low-DEF level, a
90-second alarm would begin
approximately three hours before the
tank is empty (or when the tank reaches
2.5 percent full), repeat 30 and 60
minutes after the tank runs empty, and
then repeat hourly. Poor DEF quality or
suspected tampering would trigger a
separate, less frequent warning. Derates
would not disappear entirely, as
manufacturers could still apply a derate
where continued operation would damage
the engine or aftertreatment system, and
any optional speed reduction would have
to phase in gradually — no more than one
mile per hour every five minutes. EPA is
seeking comment on all aspects of the
proposed inducement changes, including
whether the proposed warnings are
sufficient.
The warning-based system would become
mandatory for new engines no later than
model year 2029, although manufacturers
could adopt it earlier. EPA also
proposes requiring engines to compensate
for reasonable variations in DEF
concentration and generally would not
require a DEF-quality warning unless
urea concentration falls below 20
percent, compared with the normal 32.5
percent concentration.
For EMA members that sell DEF, the
proposal likely would have limited
direct effect on overall DEF demand.
Trucks and equipment would still require
DEF for SCR systems to meet emissions
standards, and operators would remain
responsible for maintaining an adequate
supply of commercially available,
properly formulated DEF. Indeed, EPA
says that DEF is now widely available
and that operators routinely purchase it
when refueling with diesel.
The commercial effects are therefore
more likely to involve purchasing
patterns than total consumption. Fewer
sudden derates could reduce emergency
purchases of packaged DEF made solely to
restore vehicle operation. At the same
time, fewer false failures and less
operator frustration may discourage
tampering and could reinforce routine
DEF use, potentially supporting pump,
bulk and regularly scheduled DEF sales.
Some industry groups are questioning
EPA’s proposal, stating that eliminating
mandatory derates will invite consumer
confusion and threatens to decrease
DEF’s availability and increase its
price, and adding that EPA should
instead allow its 2025 and early-2026
guidance — software updates, NOx sensors
in place of urea-quality sensors, and
adjusted derate schedules — to take
effect before fundamentally altering the
regulatory backdrop for DEF.
Comments are due by August 29, 2026
(Docket No. EPA-HQ-OAR-2026-0728), and
EPA will hold virtual public hearings on
July 29 and 30, 2026.
|
