DE102019219645A1 - Diagnostic procedure for an SCR catalytic converter - Google Patents

Abstract

The invention relates to a diagnostic method for an SCR catalytic converter in which a storage efficiency of the SCR catalytic converter is determined from a quotient of two integrals (26). The first integral is an integral of a difference between a modeled amount of nitrogen oxide downstream of the SCR catalytic converter and a measured sum of the amount of nitrogen oxide and the amount of ammonia downstream of the SCR catalytic converter. The second integral is an integral of an amount of ammonia dosed into the SCR catalytic converter or an amount of ammonia overdosed into the SCR catalytic converter.

Description

The present invention relates to a diagnostic method for an SCR catalytic converter. The present invention also relates to a computer program that executes each step of the method, as well as a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

An SCR (selective catalytic reduction) catalytic converter can be used to reduce nitrogen oxides in the exhaust gas from internal combustion engines, in particular from diesel engines. In this, nitrogen oxide molecules on the catalyst surface are reduced to elemental nitrogen in the presence of ammonia as a reducing agent. The reducing agent is injected in the form of an ammonia-releasing reducing agent solution (urea-water solution; HWL) upstream of the SCR catalytic converter into the exhaust system of the internal combustion engine.

In many countries the OBD (On Board Diagnosis) legislation requires monitoring of the SCR catalytic converter. If the SCR catalytic converter ages or if it is damaged so that its ability to reduce nitrogen oxide decreases, this must be communicated to the driver of a motor vehicle in which the SCR catalytic converter is installed so that he can visit a workshop. Usually, aged or damaged SCR catalytic converters are monitored by evaluating the nitrogen oxide mass flows upstream and downstream of the SCR catalytic converter. The nitrogen oxide concentrations required for this are measured with the aid of nitrogen oxide sensors, which, however, are cross-sensitive to ammonia and therefore display a sum signal of nitrogen oxides and ammonia. The increase in the sensor signal of a nitrogen oxide sensor downstream of the SCR catalytic converter can therefore indicate both an increase in the nitrogen oxide concentration due to a falling nitrogen oxide conversion rate and an increase in the ammonia concentration due to a breakthrough of pure ammonia. Since it is not possible to directly differentiate between nitrogen oxides and ammonia, the nitrogen oxide turnover can appear worse than it actually is, which can lead to a misdiagnosis.

Methods for monitoring an SCR catalytic converter can be divided into passive and active methods. In the passive process, no interventions are made in the metering strategy and thus in particular in the ammonia level of the SCR catalytic converter. The diagnosis takes place in operating phases in which a sufficiently good distinction between an intact and a defective SCR catalytic converter is possible. If the accuracy of the passive method is not sufficient to make a sufficiently robust distinction between intact and defective SCR catalytic converters, an active method can be switched to, in which advantageous conditions for a robust diagnosis are established with the help of active interventions in the reducing agent dosage amount.

An active monitoring strategy is used in the DE 10 2007 040 439 A1 described. This process makes use of the property of SCR catalytic converters that their NH3 storage capacity decreases as they age. The SCR catalytic converter is initially filled with reducing agent up to the maximum achievable ammonia storage capacity by means of an excessively stoichiometric reducing agent metering, which is also referred to as overdosing. Reaching the maximum storage capacity is recognized by the breakthrough of pure ammonia behind the SCR catalytic converter. This is also known as ammonia slip and can be measured due to the cross-sensitivity of the nitrogen oxide sensor for ammonia. Then the reducing agent dosage is reduced compared to the normal dosage, so that an under-dosage occurs or it is switched off completely. In this emptying test, the stored ammonia mass is gradually broken down again by reducing nitrogen oxide. By determining the SCR efficiency during the emptying test, the usable ammonia storage capacity can be determined indirectly.

Disclosure of the invention

The diagnostic method for an SCR catalytic converter is based on the knowledge that a value of the SCR catalytic converter referred to as storage efficiency is a better feature for assessing whether the SCR catalytic converter is intact or defective than the parameters used in previous diagnostic processes. The storage efficiency of the SCR catalytic converter is a value that is determined from a quotient of two integrals. The first integral, which is in particular in the numerator of the quotient, is an integral of an amount of ammonia downstream of the SCR catalytic converter. The second integral, which is in particular in the denominator of the quotient, is an integral of an amount of ammonia dosed into an SCR catalytic converter or an amount of ammonia overdosed into an SCR catalytic converter. The overdosed amount of ammonia is understood to mean the difference between the amount of ammonia required according to a model for the nitrogen oxide reduction in the SCR catalytic converter and the amount of ammonia actually metered in. When determining the amount of ammonia dosed or overdosed Amount of ammonia, the hydrolysis capacity of a BPU (best part unacceptable) is preferably taken into account. This takes into account the fact that an aged SCR catalytic converter can only partially hydrolyze an HWL to ammonia. The amount of HWL dosed can then be converted into the amount of ammonia dosed or overdosed in the SCR catalytic converter using a temperature-dependent characteristic curve.

With a conventional measurement of the nitrogen oxide concentrations upstream and downstream of the SCR catalytic converter to be monitored with a nitrogen oxide sensor, the value previously used for SCR diagnosis corresponds in the conventional sense to the nitrogen oxide conversion rate of the SCR catalytic converter if there is no ammonia in the exhaust gas behind the SCR catalytic converter to be monitored is. If, however, ammonia is present in the exhaust gas, this proportion is incorrectly interpreted by the sensor as nitrogen oxide and therefore not the actual nitrogen oxide conversion rate, but a lower value is calculated. The correction of the nitrogen oxide sensor signal, e.g. on the basis of a model, is error-prone and leads to a greater spread of the monitoring results. By evaluating the dosing phases or overdosing phases, this effect is reduced because it is typically mainly ammonia that is detected here.

The diagnostic method using the storage efficiency is particularly well suited for monitoring an SCR catalytic converter close to the engine, for example an SCR catalytic converter which is arranged on a particle filter (SCRF) in an exhaust system with two SCR catalytic converters installed one behind the other, since this is the first SCR catalytic converter. Catalytic converter the ammonia content in the exhaust gas is higher than behind the second SCR catalytic converter or behind a single SCR catalytic converter and thus the uncertainty of the efficiency calculation tends to be higher. In addition, the ammonia content of the exhaust gas upstream of the first SCR catalytic converter in the exhaust gas is normally known, since it results directly from the metering into the exhaust system. In principle, however, the diagnostic method can also be used for the second SCR catalytic converter in a system with two SCR catalytic converters. This is particularly useful when a second metering valve is used between the two SCR catalytic converters.

• In einer ersten Ausführungsform als passives Diagnoseverfahren wird dieses durchgeführt, wenn eine Ammoniak-Überdosierphase des SCR-Katalysators erkannt wurde. Das zweite Integral ist hierbei ein Integral der in den SCR-Katalysator überdosierten Ammoniakmenge. Diese Ausführungsform des Verfahrens ist insbesondere dazu geeignet, einen gealterten SCR-Katalysator zu erkennen, der in einem SCR-Katalysatorsystem mit mehreren SCR-Katalysatoren als erster SCR-Katalysator verbaut ist.

The method can in particular be implemented in four different embodiments:

• In a first embodiment as a passive diagnostic method, this is carried out when an ammonia overdosage phase of the SCR catalytic converter has been detected. The second integral here is an integral of the amount of ammonia overdosed into the SCR catalytic converter. This embodiment of the method is particularly suitable for recognizing an aged SCR catalytic converter which is installed as the first SCR catalytic converter in an SCR catalytic converter system with a plurality of SCR catalytic converters.

In a further passive embodiment of the diagnostic method, this is carried out when an ammonia metering phase of the SCR catalytic converter has been recognized. The second integral, however, is an integral of the total amount of ammonia metered into the SCR catalytic converter. This embodiment of the method is particularly suitable for detecting a total failure of an SCR catalytic converter which is installed as a second SCR catalytic converter in a system with several SCR catalytic converters.

In these two passive embodiments of the diagnostic method, it is preferred that the ammonia overdosing phase or ammonia dosing phase is detected over a first period of time. The first integral and the second integral are then each formed over a second period of time which is longer than the first period in order to achieve an evaluation time that enables a robust diagnosis. The length of the first period can in particular be determined by an amount of ammonia metered into the SCR catalytic converter, an exhaust gas mass flow, a nitrogen oxide mass flow, or a nitrogen oxide concentration in the exhaust gas upstream of the SCR catalytic converter.

In a third embodiment of the diagnostic method, an active ammonia overdosage is carried out into the SCR catalytic converter. The second integral is an integral of the amount of ammonia overdosed into the SCR catalytic converter. This embodiment of the diagnostic method is particularly suitable for detecting an aged SCR catalytic converter that is installed as the first SCR catalytic converter in a system with several SCR catalytic converters.

In a fourth embodiment of the diagnostic method, ammonia is actively metered into the SCR catalytic converter. The second integral is an integral of the total amount of ammonia metered into the SCR catalytic converter. This embodiment of the diagnostic method is particularly suitable for detecting a total failure of an SCR catalytic converter which is installed in an SCR catalytic converter system with several SCR catalytic converters as a second SCR catalytic converter.

In the active embodiments of the diagnostic method, the ammonia overdosage or ammonia dosage is preferably carried out over a first period of time, the first integral and the second integral being formed over a second period of time which is longer than the first Period is. This achieves a sufficiently long evaluation time for a robust implementation of the diagnostic method.

If an ammonia sensor is arranged downstream of the SCR catalytic converter in the exhaust system or if a multi-gas sensor is arranged there, which among other things. can determine the amount of ammonia, then this value can be used directly in the first integral. If there is only one nitrogen oxide sensor downstream of the SCR catalytic converter that reacts cross-sensitively to ammonia, the amount of ammonia can be calculated as the difference between an amount of nitrogen oxide in the exhaust system and a sum of the amount of nitrogen oxide measured by the nitrogen oxide sensor and the amount of ammonia downstream of the SCR catalytic converter. When the diagnostic method is carried out in an overdosing phase, the amount of nitrogen oxide in the exhaust system that is used to calculate the first integral is a modeled amount of nitrogen oxide downstream of the SCR catalytic converter. In a preferred embodiment of the method, the model used for this is the nitrogen oxide model of a WPA (worst part acceptable). Another preferred embodiment of the method is the nitrogen oxide model of a BPU (best part unacceptable). If, on the other hand, the diagnostic method is carried out in a metering phase, then the amount of nitrogen oxide in the exhaust system that is used to calculate the first integral is a measured amount of nitrogen oxide upstream of the SCR catalytic converter.

The computer program is set up to carry out each step of the method, in particular when it runs on a computing device or on an electronic control device. It enables the implementation of different embodiments of the method on an electronic control unit without having to make structural changes to it. For this purpose, it is stored on the machine-readable storage medium. By uploading the computer program to a conventional electronic control device, the electronic control device is obtained, which is set up to diagnose an SCR catalytic converter by means of the diagnostic method.

Figure list

• 1 zeigt schematisch einen SCR-Katalysator, der mittels Ausführungsbeispielen des erfindungsgemäßen Verfahrens diagnostiziert werden kann.
• 2 zeigt ein Ablaufdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.
• 3 zeigt ein Ablaufdiagramm eines anderen Ausführungsbeispiels des erfindungsgemäßen Verfahrens.
• 4 zeigt ein Ablaufdiagramm noch eines anderen Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

Embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows schematically an SCR catalytic converter which can be diagnosed by means of exemplary embodiments of the method according to the invention.
• 2 shows a flow chart of an embodiment of the method according to the invention.
• 3 shows a flow chart of another exemplary embodiment of the method according to the invention.
• 4th shows a flow chart of yet another exemplary embodiment of the method according to the invention.

Embodiments of the invention

An internal combustion engine 10 of a motor vehicle that is in 1 is shown, has in its exhaust system 11 an SCR catalytic converter 12th on. In a reducing agent tank 13th is a reducing agent solution 14th stored in the form of a urea-water solution. A funding module 15th at the bottom of the reducing agent tank 13th is set up to the reducing agent solution 14th to a dosing module 16 to transport. This is upstream of the SCR catalytic converter 12th in the exhaust system 11 arranged. Upstream of the dosing module 16 is in the exhaust system 11 a first nitrogen oxide sensor 17th arranged. Downstream of the SCR catalyst 12th is in the exhaust system 11 a second nitrogen oxide sensor 18th arranged. Both nitrogen oxide sensors 17th , 18th are cross-sensitive to ammonia. The internal combustion engine 10 and the dosing module 16 are controlled by an electronic control unit 19th controlled.

This also receives the data from the nitrogen oxide sensors 17th , 18th . The following exemplary embodiments of the diagnostic method according to the invention are described using this simple SCR catalytic converter system. However, all of the following exemplary embodiments of the diagnostic method can also be used in a more complex SCR catalytic converter system, in the one downstream of the SCR catalytic converter 12th another SCR catalytic converter in the exhaust system 11 is arranged and in which a further metering module can optionally be arranged between the two SCR catalytic converters.

The sequence of a first exemplary embodiment of the diagnostic method is shown in FIG 2 shown. After a start 20th a calculation is made during the process 21 a value α for a metering phase of, for example, 100 mg ammonia. This results from Formula 1: $$\mathrm{\alpha }=\frac{{\displaystyle \int \left(\text{dmNH}{3}_{ist}\right)\text{German}}}{{\displaystyle \int \left(\text{dmNH}{3}_{\text{should}}\right)\text{German}}}$$

Here referred MNH3 _to the amount of ammonia in accordance with values of the first nitrogen oxide sensor 17th to reduce the from the internal combustion engine 10 emitted nitrogen oxides is required and MNH3 _is designated by means of the metering 12th actually in the SCR catalytic converter 12th dosed amount of ammonia.

An examination is then carried out 22nd whether the general release conditions for the diagnosis are met. These release conditions include a suitable operating mode of the internal combustion engine 10 , a release of the nitrogen oxide sensors 17th , 18th , a specified temperature range of the SCR catalytic converter 12th , a maximum filtered gradient of the temperature of the SCR catalyst 12th , predetermined ranges of the exhaust gas mass flow or nitrogen oxide mass flow and the nitrogen oxide concentration at the first nitrogen oxide sensor 17th , as well as a predetermined range of the ammonia level of the SCR catalytic converter 12th .

mNH3_OvrDos bezeichnet dabei die Überdosiermenge an Ammoniak. mNH3_Ds bezeichnet die Ammoniakmenge stromabwärts des SCR-Katalysators 12. Diese kann mittels Formel 3 berechnet werden: $$\text{mNH}{3}_{\text{Ds}}=\text{m}{\left(\text{NOx}+\text{NH}3\right)}_{\text{Mess}}-{\text{mNOx}}_{\text{Mod}}$$

A comparison is made if the release conditions are met 23 of the value α with a threshold value which in the present case is, for example, 1.2. If this threshold value has been exceeded, it is recognized that an overdosing phase of the SCR catalytic converter 12th has started and the procedure will be in an initial period 31 continued. In a first calculation step 24 the overdosing amount is calculated. A comparison is then made 25th the overdosing amount with an evaluation threshold, which in the present case is, for example, 300 mg ammonia. If this evaluation threshold is not reached or exceeded, the method is terminated. Otherwise, the procedure will be in an additional period of time 32 continued so the first period 31 and the additional period 32 together form a second period that is longer than the first period 31 is. The additional period 32 ends when an integrated exhaust gas mass has been in operation since the beginning of the second period 32 exceeds a threshold value of, for example, 0.5 kg in the present case. In the additional period 32 an additional evaluation phase takes place at the end of which the storage efficiency in NH3 _{Eff is} calculated according to formula 2: $$\text{NH}{3}_{\text{Eff}}=1-\frac{{\displaystyle \int \left(\text{dmNH}{3}_{\text{Ds}}\right)\text{German}}}{{\displaystyle \int \left(\text{dmNH}{3}_{\text{OvrDos}}\right)\text{German}}}$$

mNH3 _OvrDos refers to the overdosage of ammonia. _{mNH3 Ds} denotes the amount of ammonia downstream of the SCR catalytic converter 12th . This can be calculated using formula 3: $$\text{mNH}{3}_{\text{Ds}}=\text{m}{\left(\text{NOx}+\text{NH}3\right)}_{\text{Mess}}-{\text{mNOx}}_{\text{Mod}}$$

Here, m (NOx + NH3) _Mess denotes the means of the second nitrogen oxide sensor 18th measured sum of the amount of nitrogen oxide and the amount of ammonia downstream of the SCR catalytic converter 12th . _{mNOx Mod} describes the amount of nitrogen oxide on the second nitrogen oxide sensor 18th which can be determined using a model. The two integrals are thereby over the first period 31 and the additional period 32 educated. A comparison is then made 27 the storage efficiency NH3 _Eff with a threshold value that is used to distinguish between an intact and a defective SCR catalytic converter 12th serves. Depending on the result of this comparison, a diagnosis is made 28 of the SCR catalytic converter 12th as functional or a diagnosing 29 of the SCR catalytic converter 12th as damaged.

In the comparison 25th Alternatively, a threshold can also be set as a function of temperature and exhaust gas mass flow for the modeled ammonia level of the SCR catalytic converter for the transition to the additional period 32 can be specified. In a further alternative, the threshold for the overdosing amount is queried, but only in the additional period 32 changed after the current overdosing phase has ended.

In a second exemplary embodiment of the method, in step 22nd Checked release conditions additionally that a difference between the actual ammonia level of the SCR catalytic converter and the maximum ammonia level at which no ammonia slip is to be expected with an WPA has at least a value of, for example, 200 mg. The current actual level results from a model of the SCR catalytic converter 12th which is calculated for the current dosing strategy. Alternatively, the actual level can be determined in a model calculated separately for the diagnosis. The maximum ammonia level at which no ammonia slip is to be expected with the WPA is taken from a characteristic map as a function of the temperature of the SCR catalytic converter and the exhaust gas mass flow. Alternatively, the actual fill level is shown in the separately calculated model of the diagnosis when the control unit is initialized 19th set to the highest possible value for the ammonia load of 6 g, for example, whereby a maximum estimate of the fill level is realized. With increasing temperature of the SCR catalytic converter 12th the ammonia level drops due to the maximum storage capacity. When the temperature subsequently falls, memory locations become free and the diagnosis can be released. Also any nitrogen oxide conversion in the SCR catalytic converter 12th can reduce the level, which also frees up ammonia storage locations. For comparison 23 no threshold value is used, but the integration of the above-mentioned ammonia quantities is started as soon as the metered quantity at the metering valve 12th is greater than a first threshold of, for example, 5 mg / s in the present case and is maintained until the dosing amount is below a second again The threshold of, for example, 3 mg / s in the present case drops. As a result, there is no overdosing, just a normal dosing of ammonia into the SCR catalytic converter 12th recognized. The transition from the first period 31 for the additional period 32 takes place when a threshold of dosed ammonia is exceeded, which depends on the temperature of the SCR catalytic converter 12th and the exhaust gas mass flow averaged over the diagnostic period or the maximum temperature of the SCR catalytic converter is selected. The further method steps are carried out as in the first exemplary embodiment of the method, with in step 26th however, the storage efficiency NH3 _Eff is calculated according to formula 4: $$\text{NH}{3}_{\text{Eff}}=1-\frac{{\displaystyle \int \left(\text{dmNH}{3}_{\text{Ds}}\right)\text{German}}}{{\displaystyle \int \left(\text{dmNH}{3}_{\text{DOS}}\right)\text{German}}}$$

_{Here, mNH3 Dos} denotes the amount of ammonia to be metered. Instead of the modeled amount of nitrogen oxide mNOx _Mod in formula 3, when using formula 4 to calculate mNH3 _Ds according to formula 5, a using the first nitrogen oxide sensor 17th upstream of the SCR catalyst 12th measured amount of nitrogen oxide mNOx _Mess used: $$\text{mNH}{3}_{\text{Ds}}=\text{m}{\left(\text{NOx}+\text{NH}3\right)}_{\text{Mess}}-{\text{mNOx}}_{\text{Mess}}$$

A third embodiment of the method according to the invention is shown in FIG 3 shown. In the first period 31 will every time the terms of the steps 22nd and 23 are fulfilled, the calculation of the overdosing amount 24 then restarted the process. Only when one of the release conditions according to step 22nd is no longer fulfilled or if in step 23 the value α no longer exceeds the threshold value, the comparison takes place 25th the one on the last run through of the step 24 calculated overdosing quantity with the evaluation threshold. If the evaluation threshold is exceeded, the method is continued in the same way as in the first two exemplary embodiments and in formula 2 the integrals over the first period of time are determined 31 and the additional period 32 considered. Will be in the crotch 25th However, if the evaluation threshold is not exceeded, a reset takes place 40 of all integrators and the diagnostic procedure is restarted.

In a fourth exemplary embodiment of the diagnostic method, according to the flow chart according to 3 A diagnosis can also be made if there is no overdose, only normal dosing. The exam 22nd and the comparison 23 are carried out as in the second embodiment. The calculation of the storage efficiency in step 26th then takes place as in the second exemplary embodiment using formula 4.

The sequence of a fifth exemplary embodiment of the method according to the invention is shown in FIG 4th shown. In doing so, in step 22nd not only is the release conditions of the second exemplary embodiment checked, but a check also takes place as to whether conditions for an overdosing phase are met. If this is the case, it takes place in the first period 31 first an active overdose 50 of ammonia with a value of, for example, α = 1.5 in the present case. The overdosage is in step 24 integrated and in the crotch 25th compared with the evaluation threshold. If this is reached or exceeded, the method is as in the first exemplary embodiment with the steps 26th to 29 continued with the calculation in step 26th takes place according to formula 2. Otherwise the process is restarted.

In the fifth exemplary embodiment, the overdosing can alternatively also take place by increasing the amount of ammonia mNH3 which _{is intended} to reduce the amount of the internal combustion engine 10 emitted nitrogen oxides is required, an offset of, for example, 20 mg / s is added.

In a sixth exemplary embodiment of the diagnostic method, there is no active overdosing for diagnosis, but only active dosing. In the flow chart according to 4th is then in step 22nd In addition to the general release conditions, it is checked whether the conditions for a dosage are met. In step 50 instead of overdosing, only normal dosing takes place. The dosing amount is in step 24 integrated and in step 25th compared with the evaluation threshold. The procedural steps 26th to 29 are carried out as in the second exemplary embodiment of the diagnostic method, where in step 26th Formula 4 is used to calculate the _{NH3 Eff storage efficiency.}

QUOTES INCLUDED IN THE DESCRIPTION

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Patent literature cited

• DE 102007040439 A1 [0005]

Claims (10)

Diagnostic method for an SCR catalytic converter (12) in which a storage efficiency of the SCR catalytic converter (12) is determined from a quotient of two integrals (26), wherein - The first integral is an integral of an amount of ammonia downstream of the SCR catalytic converter (12), and - The second integral is an integral of an amount of ammonia dosed into the SCR catalytic converter (12) or an amount of ammonia overdosed into the SCR catalytic converter (12). Diagnostic procedure according to Claim 1 , characterized in that it is carried out when an ammonia overdosage phase of the SCR catalytic converter (12) has been detected, the second integral being an integral of the amount of ammonia overdosed into the SCR catalytic converter (12). Diagnostic procedure according to Claim 1 , characterized in that it is carried out when an ammonia metering phase of the SCR catalytic converter (12) has been detected, the second integral being an integral of the amount of ammonia metered into the SCR catalytic converter (12). Diagnostic procedure according to Claim 2 or 3 , characterized in that it is carried out when an ammonia overdosing phase or ammonia dosing phase has been detected over a first period of time (31), the first integral and the second integral each being formed over a second period of time which is longer than the first period of time is. Diagnostic procedure according to Claim 1 , characterized in that an active ammonia overdosage into the SCR catalytic converter (12) takes place during its implementation, the second integral being an integral of the amount of ammonia overdosed into the SCR catalytic converter (12). Diagnostic procedure according to Claim 1 , characterized in that an active ammonia metering into the SCR catalytic converter (12) takes place during its implementation, the second integral being an integral of the amount of ammonia metered into the SCR catalytic converter (12). Diagnostic procedure according to Claim 5 or 6th , characterized in that it is carried out when an active ammonia overdosing or ammonia dosing has been carried out over a first period of time (31), the first integral and the second integral each being formed over a second period of time which is longer than the first Period is. Computer program which is set up, each step of the method according to one of the Claims 1 to 7th perform. Machine-readable storage medium on which a computer program is based Claim 8 is stored. Electronic control unit (19) which is set up to use a diagnostic method according to one of the Claims 1 to 7th diagnose an SCR catalytic converter (12).

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