SCR and AdBlue: what the law makes the system detect

A Euro VI truck that relies on a reagent to reduce its NOx emissions carries a second tank and, under the rule this page describes, a dashboard indicator of the reagent level placed close to the fuel gauge. What that indicator warns about, and what happens once the warning is ignored, is not left wholly to the manufacturer. It is written down in detail, with numbers — just not in the document an operator would open first.

The rule is three documents away from where you would look

Regulation (EC) No 595/2009 is the Euro VI regulation, and it does not contain the rule. Article 5(4)(k) instructs the Commission to adopt specific provisions ensuring the correct operation of NOx control measures, and says what they have to achieve: that vehicles cannot be operated if the NOx control measures are inoperative due, for example, to lack of any required reagent, incorrect exhaust gas recirculation flow or deactivation of EGR. That is the whole of Article 5(4)(k) — a purpose, not a threshold.

The implementing measure is Commission Regulation (EU) No 582/2011; the consolidated version on EUR-Lex carries the date 12 March 2026. Article 3(1) makes type-approval conditional on compliance with a list of annexes that includes Annex XIII, headed “Requirements to ensure the correct operation of NOx control measures”. Open it and most of it points somewhere else. Point 3.1 says the maintenance requirements “shall be those set out in paragraph 3 of Annex 11 to UNECE Regulation No 49”, and points 4.1 to 9.1 do the same for the warning system, the inducement system, reagent availability, reagent quality, consumption and dosing, and tampering — though point 9.1, the tampering one, as printed names paragraph 6 of Annex 11, not paragraph 9. What is left is a list of substitutions — which sentence to read in place of a named UN paragraph. Most fit the UN text to the EU framework: the information document, the documentation package, “the territory of the Union” for “the relevant region”, the definition of CDmin and its demonstration, dual-fuel. Points 4.1.1 and 5.1.1, and point 2.1.2.2.5 inside an alternative approval route, concern the rescue services. Two keep figures the UN annex already carries but tie them to an EU phase-in: point 7.1.2 keeps “the value of 900mg/kWh” in place of the NOx emission limit, “upon request of the manufacturer for the purpose of point 7.1”, and point 8.1.1 the 50 % deviation threshold, both for “the phase-in period specified in Article 4(7) of this Regulation” rather than the one in the UN text.

Which published version of that annex does the pointing reach? Regulation (EU) No 582/2011 answers once, in the footnote on its reference to the UN regulation: “Regulation No 49 of the Economic Commission for Europe of the United Nations (UN/ECE) … (OJ L 171, 24.6.2013, p. 1).” That is the 06 series of amendments. It took an amending act to get there: Commission Regulation (EU) No 133/2014 updated the references, its recital 6 reasoning that “[s]ince a 06 series of amendments of UNECE Regulation No 49 has been adopted … it is necessary to update the references of Euro VI to UNECE Regulation No 49”, with the same OJ L 171 of 24 June 2013 in its footnote. The consolidated text of 12 March 2026 still gives that publication, and the phrase “07 series” appears nowhere in it. The UN text itself has moved on — the EU published it again as UN Regulation No 49 [2023/64] at OJ L 14 of 16 January 2023, carrying the 07 series in force since 7 January 2022 — but the EU measure has not been amended to follow. So every figure below is read off the 2013 publication, and where the 2023 one differs this page gives both. Paragraph 1.1, identical in both, covers M1, M2, N1 and N2 vehicles with a reference mass over 2,610 kg and all M3 and N3 — the Euro VI scope Article 2 of Regulation (EC) No 595/2009 also sets.

Not every vehicle in that scope has to meet Annex 11 on this point. Under point 2.1.1 of Annex XIII, “If requested by the manufacturer”, M2 and N1 vehicles, M1 and N2 vehicles with a maximum permissible mass not exceeding 7.5 tonnes, and M3 Class I, Class II, Class A and Class B vehicles with a permissible mass not exceeding 7.5 tonnes may instead comply with Annex XVI to Regulation (EC) No 692/2008, with the exceptions listed in point 2.1.2; under Article 3(4) of Regulation (EU) No 582/2011, the route is not open to dual-fuel engines and vehicles, nor to the approval of an engine system or engine family as a separate technical unit. That annex has its warning activate at “a driving range of at least 2 400 km” before the reagent tank is empty, and has the manufacturer select one of four inducement approaches: no engine restart after a countdown, no start after refuelling, a fuel lockout, or a speed restriction after which engine restarts are prevented. Regulation (EC) No 692/2008 was repealed “as from 1 January 2022” by Article 19 of Commission Regulation (EU) 2017/1151; the consolidated Annex XIII of 12 March 2026 still points to it. Even on that route, point 2.1.2 keeps the Annex XIII (and so Annex 11) rules on reagent quality and on consumption and dosing, with the Annex XVI warning system in place of Annex 11’s. Everything below describes Annex 11 as it applies without that alternative.

Four things the system has to notice

Annex 11 asks for more than an AdBlue gauge. It sets four monitoring duties, three of which run counters of engine operating hours. Paragraph 6 covers availability and requires a dashboard level indicator close to the fuel gauge. It has no counter of its own in the list at point A.2.4.1.1 of Appendix 2, and under point A.2.3.3 warning and inducement there are activated or deactivated after assessment of the reagent quantity in the tank and “shall not depend upon the status of any associated DTC”. Paragraph 7 covers quality, against a minimum concentration CDmin the manufacturer declares and proves at type-approval, counted under 7.1.3. Paragraph 8 covers consumption and dosing, comparing what was used against what the engine demanded, with a counter for each under 8.2.1. Paragraph 9 covers tampering, and names two failures — impeding of the EGR valve, and failure of the anti-tampering monitoring itself, including removal or deactivation of any sensor it needs — counted under 9.2.2.1 and 9.2.3.1. Five kinds of counter in all: point A.2.4.1.1 requires “at least 5 counters” across those five conditions, and Appendix 5 lists the same five types among the information to be readable off-board.

Two things in that table read as more fixed than they are. None of the three tank-level triggers is a fixed point: 6.2.1 and 6.3.1 each end “or a higher percentage at the choice of the manufacturer”, and 6.3.2 fires either on an empty tank — the dosing system can no longer draw from it — or at any level below 2.5 per cent the manufacturer chooses. And the dosing row carries its own exception: under 8.4.2 the warning “shall not be required where the interruption is demanded by the engine ECU because the vehicle operating conditions are such that the vehicle’s emission performance does not require reagent dosing”.

The hours are engine operating hours, not calendar time: point A.2.4.1.1 has the counters record “the number of hours during which the engine has been operated” while a fault is detected, so time parked with the engine off does not count, while time idling does. And paragraphs 7.3.3, 8.5.3 and 9.4.3 all say the same thing: the number of hours before inducement “shall be reduced in case of a repetitive occurrence of the malfunction”, by the mechanism in Appendix 2.

Two stages, and the second one is 20 km/h

Paragraph 5.1 gives the shape of the whole thing in one sentence: a two-stage driver inducement system, starting with a low-level inducement — a performance restriction — followed by a severe inducement, effective disablement of vehicle operation. Paragraph 5.2 then lifts a whole class back out. The requirement “shall not apply” to engines or vehicles for use by the rescue services, or to those designed and constructed for use by the armed services, civil defence, fire services and forces responsible for maintaining public order; permanent deactivation “shall only be done by the engine or vehicle manufacturer”. Point 5.1.1 of Annex XIII restates that for EU purposes, replacing the second limb with the “engines or vehicles specified in point (b) of Article 2(3) of Directive 2007/46/EC” — a Directive repealed with effect from 1 September 2020 by Regulation (EU) 2018/858, whose Article 88 has references to it construed as references to that Regulation. Nothing in the rest of this section reaches them.

The low-level stage is paragraph 5.3. It cuts the maximum available engine torque by 25 per cent between the peak torque speed and the governor breakpoint, and the maximum available reduced torque below the peak torque speed “shall not exceed the reduced torque at that speed”. It is activated when the vehicle becomes stationary for the first time after the triggering condition — a moment the 2013 text leaves undefined and the 2023 one pins down in a footnote, at the latest one minute after road speed has fallen to zero, with no need to engage a park, trailer or hand brake. The cut arrives at a stop, not on the move — a different reading of a torque curve from the one on a brochure.

The severe stage, paragraph 5.4, is not one system but a choice plus a backstop: the manufacturer fits “at least one” of three, and the fourth regardless. A “disable after restart” system limits the vehicle to 20 km/h after the engine has been shut down at the driver’s request. A “disable after fuelling” system does so once the fuel tank level has risen by a measurable amount, which “shall not be more than 10 per cent of the fuel tank capacity” and is approved by the Type Approval Authority on the technical capabilities of the fuel level meter and a declaration by the manufacturer. A “disable after parking” system does so after the vehicle has stood for more than an hour. The backstop, paragraph 5.4.4, limits it to 20 km/h at the first stop after eight hours of engine operation if none of the other three has been activated.

Cold weather is written into the rule

Under paragraph 2.4.1 the manufacturer “may use a heated or a non-heated reagent tank and dosing system, in accordance with the general requirements of paragraph 2.3.1” — which, in the EU wording of Annex XIII point 2.1.5, require any engine system in scope to “retain its emission control function during all conditions regularly pertaining in the territory of the Union, especially at low ambient temperatures”. Beyond that shared duty, each carries different ones. For a heated system, paragraph 2.4.2.1 says that if the reagent has frozen, the manufacturer “shall ensure that reagent is available for use within a maximum of 70 minutes after the start of the vehicle at 266 K (- 7 °C) ambient temperature”. The demonstration soaks tank and dosing system at 255 K (−18 °C) “for 72 hours or until the bulk of the reagent becomes solid”, then starts and runs the engine at 266 K: 10 to 20 minutes idling, followed by up to 50 minutes at no more than 40 per cent load.

A non-heated system is not held to the 70-minute availability requirement of paragraph 2.4.2.1; it carries consequences instead. Under paragraph 2.4.3.1 the warning system shall be activated if no dosing occurs at an ambient temperature at or below 266 K, and under 2.4.3.2 the severe inducement system shall be activated if no dosing occurs at or below that temperature within a maximum of 70 minutes after vehicle start. Paragraph 2.4.1.1 requires the use of a non-heated tank and dosing system to be indicated in the written instructions to the owner — so on a used vehicle, those instructions are where that choice is written down; the vehicle’s other papers are taken in turn in buying a used truck.

Paragraph 2.3.2 sets the conditions in which the emission control monitoring system “shall be operational”: ambient temperatures between 266 K and 308 K (−7 °C and 35 °C), all altitudes below 1,600 m, engine coolant temperatures above 343 K (70 °C). Its closing sentence then lifts that envelope off one monitor: it does not apply to monitoring the reagent level in the storage tank, which “shall be conducted under all conditions where measurement is technically feasible including all conditions when a liquid reagent is not frozen”. The three tank-level rows at the top of the table are bounded by technical feasibility, not by that envelope.

Consumption is the manufacturer’s figure to state

There is no litres-per-100-km figure anywhere in this chain. Paragraph 3.4 of Annex 11 requires the manufacturer’s written instructions to specify the required reagent quality, indicate how the operator should refill the tank, and “indicate a likely rate of reagent consumption for the type of vehicle and how often it is likely to need to be replenished”. The duty is to state a likely rate; the annex sets none. A consumption figure in those instructions is the manufacturer’s own statement about its vehicle type, not a limit the law sets, and this page prints none.

What the regulation does put numbers on is the gap between actual and demanded dosing. In the 2013 text, paragraph 8.4.1 activates the warning when a deviation of more than 20 per cent is detected between average reagent consumption and average demanded consumption over a period the manufacturer defines, “which shall not be longer than the maximum period defined in paragraph 8.3.1”. Paragraph 8.3.1 sets that maximum detection period at 48 hours or the period equivalent to a demanded consumption of at least 15 litres, whichever is longer, and 8.3.2 requires at least one of two parameters to be monitored: the level of reagent in the on-vehicle tank, or the flow or quantity injected as close as technically possible to the point of injection. Those are limits on the detection period, not statements about how much a truck uses.

They are also where the two published texts differ in their numbers, which is why it was worth settling first which one applies. The 2013 text carries a paragraph 8.4.1.1 relaxing the 20 per cent to 50 until the end of a phase-in, and point 8.1.1 of Annex XIII is the EU substitution for it, tying that relaxation to Article 4(7) of Regulation (EU) No 582/2011: three years after the dates in Article 8(1) and (2) of Regulation (EC) No 595/2009, which are 31 December 2012 and 31 December 2013. Adding the three years is our arithmetic, not the Regulation’s — the later window closed at the end of 2016, so a new type approved, or a new vehicle registered, after that has no relaxation to use, and for it the 20 per cent is the threshold. The 2023 publication resolves it the other way: fifty per cent written into 8.4.1 itself, 8.4.1.1 dropped, the base period in 8.3.1 cut to five hours or at least 2 litres, and a new 8.3.1.1 extending it back to 48 hours or 15 litres where consumption is monitored by tank level or by the flow or quantity injected. Quote either pair without naming the publication and you are quoting a number, not a rule.

What the operator carries

Two duties in Regulation (EC) No 595/2009 reach the operator, not only the manufacturer. Article 7(1) says “manufacturers, repairers and operators of the vehicles shall not tamper with systems which use a consumable reagent”; Article 7(2) says operators “shall ensure that vehicles are not being driven without a consumable reagent”. Article 11(1) leaves the penalties to member states, and under Article 11(2) the infringements subject to a penalty “shall include” tampering with systems which control NOx emissions — by manufacturers, repairers and operators — and, for operators, driving a vehicle without a consumable reagent. Annex 11 paragraph 3.6 requires the owner’s instructions to say as much: “that it may be a criminal offence to use a vehicle that does not consume any reagent if the reagent is required for the reduction of emissions”.

Two more provisions sit beside those duties. Paragraph 2.5 requires every separate reagent tank to include a means of taking a sample of the fluid inside it, easily accessible without the use of any specialised tool or device. And point 3.4 of Annex II to Regulation (EU) No 582/2011, on in-service conformity, provides that engines having one of the Annex XIII counters not at zero “may not be tested”, and that this be reported to the approval authority.

What Euro 7 does with all this

Regulation (EU) 2024/1257 replaces the framework on fixed dates. Article 10(6) stops approval authorities granting emission type-approval to non-compliant new types of M2, M3, N2 and N3 vehicles and O3 and O4 trailers from 29 May 2028. From 29 May 2029, Article 10(7) has national authorities consider the certificates of conformity of non-compliant new vehicles and trailers in those categories to be no longer valid for the purposes of registration, and prohibit the registration, sale or entry into service. Two carve-outs sit against that date. Article 10(8) derogates from it until 31 December 2029 for M2 and M3 vehicles carrying a 100 per cent zero-emission target from the 2030 reporting period under Regulation (EU) 2019/1242, which may still be registered, sold or put into service on a valid Regulation (EC) No 595/2009 approval — a bus derogation. Article 10(10) sets 1 July 2031 instead for vehicles in those four categories from small-volume manufacturers. Article 20 repeals both Regulation (EU) No 582/2011 and Regulation (EC) No 595/2009 with effect from 1 July 2031. Until then both remain in force.

Euro 7 keeps the concept and moves the detail. Article 3(70) defines a low-reagent driver warning system, and Article 12(2) has national authorities verify during in-service conformity or market surveillance checks whether manufacturers have installed it correctly. The characteristics and performance of driver warning systems and inducement methods sit in Article 14(4)(k), among the things the Commission is to lay down in implementing acts, and one act made on that point exists: Commission Implementing Regulation (EU) 2025/1707 of 25 July 2025, made on Article 14(3)(a) and Article 14(4), points (j), (k), (o), (s), (t), (u) and (v). Its driver warnings and inducement methods, in Annex II, are those of the excess exhaust emissions driver warning system, which acts on the on-board monitoring status of NOx and particulate matter; the low-reagent warning system does not appear in it. For the same vehicles, the requirements for vehicles that use a reagent sit in Implementing Regulation (EU) 2025/1706, of the same date, whose Annex XVI takes them from paragraph 6.9 and Appendix 6 of UN Regulation No 154. Article 1(2) of 2025/1707 confines it to M1 and N1 and to N2 vehicles designated “Euro 7ext” and “Euro 7Gext” under Article 5 of Regulation (EU) 2024/1257, and Article 1 of 2025/1706 names the same categories, so of the heavy categories they reach only those N2 vehicles; for M2, M3, N2 and N3 the corresponding acts fall under Article 14(9), which gives the Commission until 29 November 2026. The wider step from Euro VI to Euro 7 is set out in Euro VI and Euro 7 explained. For a heavy vehicle approved under Regulation (EC) No 595/2009, the operative text is the one described here: a UN annex, published in the Official Journal in 2013, that the EU regulation points at rather than repeats.