KR102443425B1 - Method for the diagnosis of a scr system - Google Patents

Abstract

The present invention relates to a method for diagnosing an SCR system comprising a transfer pump and a metering valve. The method comprises the following steps. At the start time, judgment of a pressure fault in the SCR system is performed, and accordingly setting of the pressure control mode of the SCR system is executed. Subsequent to this, the detection of the mass deviation (Δm) of the reducing agent solution is carried out. Finally, a fault is output to the transfer pump if the mass deviation Δm exceeds the first threshold S ₁ , and the mass deviation Δm is below or equal to the first threshold S ₁ . A fault is output for the face metering valve.

Description

SCR SYSTEM DIAGNOSIS METHODS

The present invention relates to a method for diagnosing an SCR system when a pressure fault within the SCR system is determined. The present invention also relates to a computer program for executing each step of the method when running on a computer, and a machine-readable storage medium storing the computer program. Finally, the invention relates to an electronic control device configured to carry out the method according to the invention.

For the reduction of nitrogen oxides (NOx) in the exhaust gases of internal combustion engines in automobiles today, in particular SCR catalytic converters (SCR: selective catalytic reduction) are used. In this case, nitrogen oxide molecules on the surface of the SCR catalytic converter are reduced to elemental nitrogen in the presence of ammonia (NH3) as a reducing agent. The reducing agent is commercially provided in the form of a urea-water solution, also known as AdBlue®, from which ammonia is separated. A transfer pump transfers the reducing agent solution from the reducing agent tank to the metering module, which then injects the reducing agent solution into the exhaust gas line upstream of the SCR catalytic converter. Control of the metered supply is performed in an electronic control unit in which strategies for operation and monitoring of the SCR system are stored.

In the so-called "volumetric mode", usually, the generally high precision of the transfer pump; and the property that the mass of the reducing agent solution conveyed through the conveying pump while being very accurately known in the stationary state is discharged back from the system as a metered-in mass; Combined with the relatively small tolerance of the mass of the reducing agent solution conveyed via the conveying pump, a high mass precision is established on average. In this case, however, there is generally no closed-loop control circuit with respect to pressure.

"Pressure-controlled mode" is based on the principle that, in general, the transfer pump supplies the requested system pressure while adjusting to the narrowest possible pressure range centered on a determined set pressure. do. Then, the metering module meters and supplies the requested mass of the reducing agent solution through the setting of an appropriate valve opening time based on the system pressure.

In volumetric mode, if the mass balance is disturbed, for example by means of a fault in the transfer pump or in the metering module, the metered-in mass can no longer be checked directly. In this case, it is known to monitor the pressure using, for example, a pressure sensor. For this purpose, an overpressure threshold and a negative pressure threshold are determined which form an allowable pressure range centered on the set pressure. If the pressure deviates from the above permissible pressure range during metering supply, a (pressure) fault is output and a defect-containing operation is established in the SCR system. As a result, compliance with emission regulations can no longer be guaranteed.

In the case of automobiles, in a defect-containing mode, an engine check light is usually activated, which signals the driver to visit a mechanic. Optionally, in addition, an emergency mode can be set in which the SCR system is operated with different operating parameters and furthermore, for example, the output of the internal combustion engine is suppressed. In the workshop, the transfer pump and/or the metering module are repaired or exchanged "in an auspicious manner" therefor, based on the estimates or knowledge and experience of competent personnel.

DE 10 2008 005 988 A1 describes a method and apparatus for diagnosis of an exhaust gas aftertreatment device for metering and supplying reagents to the exhaust gas region. The reagent is pressurized to a metering pressure by means of a pump and then metered in. Diagnosis is carried out according to the evaluation of the pressure drop of the reagents after shutting down the pump. In this case, leakage losses of the pump are taken into account.

A so-called adaptation factor is known from DE 10 2010 002 620 A1. According to the model, the required mass of reducing agent solution metered upstream of the SCR catalytic converter and the modeled nitrogen oxide values downstream of the SCR catalytic converter are calculated. In addition, a nitrogen oxide sensor disposed downstream of the SCR catalytic converter measures the measured nitrogen oxide value. The modeled nitrogen oxide value and the measured nitrogen oxide value are compared with each other, and when there is a deviation, an overdosage or underdosage of the reducing agent solution is determined. Then, adaptation is carried out accordingly and the metering supply is increased or decreased through setting of the adaptation factor.

A method for diagnosing an SCR system comprising a transfer pump and a metering valve is therefore proposed according to the invention, in particular for an SCR catalytic converter for exhaust gas aftertreatment of an internal combustion engine in a motor vehicle. A pressure fault in the SCR system is determined if, at the start-up, for example, the system pressure between the transfer pump and the metering valve deviates from the allowable pressure range established via the overpressure threshold and the underpressure threshold during metering supply. If a pressure defect has been determined, the requested or required mass of the reducing agent solution and the actual metered mass of the reducing agent solution may differ, so that compliance with the emission regulations can no longer be guaranteed.

In a further step, the pressure control mode of the SCR system is established. In order to achieve as high a mass precision as possible of the metered reducing agent solution, the SCR system is normally operated in volumetric mode before the determination of a pressure defect, and the SCR system is switched to the pressure control mode after the determination of the defect. In pressure control mode, the transfer pump regulates the system pressure to the narrowest possible pressure range centered on the determined set pressure while supplying the requested system pressure. Accordingly, a mass deviation of the reducing agent solution may occur in the system. In a further step, said mass deviation of the reducing agent solution is detected. If the detected mass deviation exceeds the first threshold, a fault in the transfer pump can be inferred and a fault to the transfer pump is output. The principle for this lies in that the mass deviation is increased by conveying too much or too little of the mass of the reducing agent in relation to the metered mass, based on pressure control, through a fault in the transfer pump. In other cases, if the mass deviation is below or equal to the first threshold, a fault is output for the metering valve. The principle for this lies in that mass deviations through faults in the metering module are compensated for on the basis of the pressure control in the metering supply. The first threshold may preferably take on a value of up to 40%, and the first threshold may also take on a negative value, hence a value of up to -40%. The method makes it possible to diagnose already during operation the component (transfer module or metering valve) from which a pressure fault is inferred. As a result, repair or replacement of defective components is simplified, for example, in a workshop, since it is already known in advance which component is defective.

Preferably, after a pressure fault in the SCR system is determined, the setting of the fault intrinsic mode of the SCR system is performed, in which fault-specific measures are executed. As one of the measures in the fault-tolerant mode, preferably, for example, an engine check light can be activated to signal the driver of the motor vehicle to the fault-tolerant mode of the SCR system and, accordingly, the driver to drive to the repair shop. have. Accordingly, statutory provisions requiring such an effect are met. Furthermore, in the fault-tolerant mode, the SCR system is operated with other operating parameters such as, for example, metering duration and/or metered quantity and furthermore, in which the output of the internal combustion engine can be suppressed, executing at least an emergency mode for the SCR system. Other measures may also be provided. A complete shutdown of the SCR system may also be provided to prevent leakage of free ammonia, toxic to humans and the environment, from the exhaust after-treatment system through over-metering. In this process, the reducing agent solution is usually recovered from the SCR system. If this is the case, it may be provided in the above method to charge the SCR system back with the reducing agent solution before the setting of the pressure control mode.

According to a preferred aspect, the setting of the pressure control mode is realized by changing the opening period of the metering valve. If the pressure continues to increase above the set pressure, the opening period of the metering valve is increased, whereby more reducing agent solution is metered in. On the other hand, if the pressure continues to decrease below the set pressure, the opening period of the metering valve is reduced, whereby less reducing agent is metered in.

According to another aspect, the setting of the pressure control mode is realized through changing the control of the pump. In this case, depending on the pressure, the rotational speed of the pump or, in some cases, the mass conveyed simultaneously with it can be changed, so that the mass conveyed as a whole also varies.

In order to detect a mass deviation of the reducing agent solution, it can be provided that the following steps are carried out. First, the SCR catalytic converter is completely drained. If a plurality of SCR catalytic converters are provided in the SCR system, this means that all SCR catalytic converters are completely drained. Accordingly, at least one set mass flow rate of the reducing agent solution is metered upstream of the SCR catalytic converter in a substoichiometric ratio. Preferably, a plurality of said set mass flow rates are metered in at different substoichiometric ratios, in order to meet the detection range as large as possible. Following this, the nitrogen oxide concentration is detected downstream of the SCR catalytic converter. For this purpose, a nitrogen oxide sensor disposed downstream of the SCR catalytic converter may be used. In addition, nitrogen oxide concentrations are also detected upstream of the SCR catalytic converter. For this purpose, similarly a nitrogen oxide sensor arranged upstream of the SCR catalytic converter can be used. If the nitrogen oxide sensor is not provided upstream of the SCR catalytic converter, the nitrogen oxide concentration measured by the downstream nitrogen oxide sensor before the metering supply of the set mass flow rate of the reducing agent solution in a state in which the SCR catalytic converter is completely discharged is also the SCR catalyst It can be used as the NOx concentration upstream of the converter, since in this case NOx was not reduced via the SCR catalytic converter. From the difference between the nitrogen oxide concentration downstream of the SCR catalytic converter and the nitrogen oxide concentration upstream of the SCR catalytic converter, the actual mass flow rate of the reducing agent solution flowing through the SCR catalytic converter is calculated, taking into account the substoichiometric ratio and the total exhaust gas mass flow rate. do. At the actual mass flow rate, the mass of the reducing agent solution actually metered can be calculated while the set mass flow rate is related to the requested mass of the reducing agent solution. Finally, in order to calculate the mass deviation, a comparison of the set mass flow rate and the actual mass flow rate is performed.

Alternatively, the following steps may be carried out to detect a mass deviation of the reducing agent solution. Before the pressure control mode is set, an adaptation factor, for example according to DE 10 2010 002 620 A1, can be detected in a known manner and subsequently stored as a nominal adaptation factor. After the pressure control mode is set, the adaptation factor is reset and a new adaptation is started. During the pressure control mode, in the same way, a new adaptation factor is learned over the learning time according to the new adaptation. Finally, a comparison of the nominal adaptation factor and the new adaptation factor is performed to calculate the mass deviation.

The computer program herein is configured to execute each step of the method herein, particularly when executed on a computer or control device. The computer program of the present invention enables implementation of the method of the present invention in a conventional electronic control device without the need to implement structural changes to the conventional electronic control device. To this end, the computer program of the present application is stored in a machine-readable storage medium.

By installing the computer program of the present invention in a conventional electronic control device, an electronic control device configured to perform diagnosis of the SCR system is secured.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention are shown in the drawings and are described in more detail in the following description.

1 is a schematic diagram showing an SCR system for an SCR catalytic converter in an exhaust gas line of an internal combustion engine, to which the method according to the invention can be applied.
FIG. 2 is a graph showing the pressure of the SCR system of FIG. 1 over time in the volume mode.
3 is a flow chart showing a first embodiment of a method according to the invention;
4 is a flow chart showing a second embodiment of the method according to the invention;
5 is a graph showing the pressure of the SCR system of FIG. 1 and the mass deviation of the reducing agent solution over time, respectively, in the pressure control mode according to an embodiment of the method according to the present invention.

1 shows a schematic diagram of an SCR system 1 for an SCR catalytic converter 2 in an exhaust gas line 3 of an internal combustion engine 4 . The SCR system 1 comprises a transfer module 10 with a transfer pump 11 , which transfers the reducing agent solution from the reducing agent tank 12 to the metering module 14 via a pressure line 13 . do. Then, via the metering valve 15 in the metering module 14 , the reducing agent solution is metered into the exhaust gas line 3 upstream of the SCR catalytic converter 2 . The reducing agent solution that has not been metered flows back into the reducing agent tank 12 via a return 16 connected to the pressure line 13 . In the return 16 , a return throttle 17 is arranged which limits the mass of the reducing agent solution flowing through the return 16 . A pressure sensor 18 is also arranged in the pressure line 13 and measures the pressure p of the reducing agent solution therein. In the exhaust gas line 3, a first nitrogen oxide sensor 31 is disposed downstream of the SCR catalytic converter 2 to measure the nitrogen oxide concentration (NOxN) downstream of the SCR catalytic converter 2 at that location, , the second nitrogen oxide sensor 32 is disposed upstream of the SCR catalytic converter 2 and measures the nitrogen oxide concentration (NOxV) upstream of the SCR catalytic converter 2 at the corresponding position. Also provided is an electronic control device 5 which is connected to at least the transfer module 10 or the transfer pump 11 and the metering module 14 or the metering valve 15 to control them. Further, the pressure sensor 18 and the two nitrogen oxide sensors 31 , 32 are connected to an electronic control device 5 and transmit their measured values to this electronic control device.

In general, the SCR systems are operated in volumetric mode, in which the mass of the reducing agent solution conveyed via a transfer pump 11 is metered in through a metering valve 15 as a metered mass. In this case, on average, a high mass precision is set, but in the case of pressure p there is no closed-loop control circuit. In FIG. 2 , two pressure profiles, p ₁ and p ₂ , are plotted as a graph of pressure p over time t for the volumetric mode, both pressure profiles causing pressure defects. In the first region 100 , in which the metering valve 15 is closed, the transfer pump 11 delivers the reducing agent, whereby the pressure p for the two pressure profiles p ₁ and p ₂ is equal to the ambient pressure p from _a ) until the set pressure (p _s ) is reached. From the “Begin of Injection Point” (BIP), the metering valve 15 is opened, and the reducing agent solution is metered into the exhaust gas line 3 . The two pressure profiles p ₁ and p ₂ differ from each other in the second region 101 in which the metered supply takes place. The first pressure profile p ₁ represents a defect in the transfer pump 11 causing more reducing agent solution to be delivered than intended or the metering valve 15 causing less reducing agent solution to be metered in than intended. . Correspondingly, the first pressure profile p ₁ continues to rise and eventually exceeds the overpressure threshold p _o . The second pressure profile p ₂ is, on the contrary, of the transfer pump 11 allowing less reducing agent solution to be delivered than intended or the metering valve 15 allowing more reducing agent solution to be metered in than intended. indicates a defect. Correspondingly, the second pressure profile p ₂ decreases and eventually falls below the negative pressure threshold p _u . If the pressure p, after the “injection start point” (BIP), deviates from the allowable pressure range between the overpressure threshold p _o and the negative pressure threshold p _u , a pressure fault is determined 200 .

3 shows a flowchart of a first embodiment of the method according to the invention. As previously described, if a pressure defect in the SCR system 1 is determined 200, the setting 201 of the defect intrinsic mode FM is performed. In this case, on the one hand, the check engine light is activated (202). In the case of the embodiment in which the SCR system 1 is used in a motor vehicle, an engine check light is arranged on the instrument cluster (both not shown), whereby the engine check light signals to the driver of the vehicle a fault-tolerant mode (FM). will be guided to In addition, in the fault-tolerant mode (FM), an emergency mode 203 is also established, in which the SCR system 1 is operated with different operating parameters. In addition, in many embodiments, during the emergency mode 203 , the output of the internal combustion engine 5 may be suppressed. In the case of the embodiment available here, in addition the SCR system 1 is completely evacuated in emergency mode 203, ie to prevent free ammonia from leaking out of the exhaust gas line 3 through overmetering, The reducing agent solution is transferred back into the reducing agent tank 12 . Accordingly, in the case of this embodiment, the reducing agent solution refilling 204 of the SCR system 1 is performed.

According to the invention, the pressure control mode DM for the SCR system 1 is established. This is realized, in the case of the embodiments described herein, via a change 205 of the opening period of the metering valve 15 . In still other embodiments, the setting of the pressure control mode DM may be realized by changing the control of the transfer pump 11 .

)이 SCR 촉매 컨버터(2)의 상류에서 계량 공급된다(211).In the first embodiment shown in Fig. 3, the detection of the mass deviation [Delta]m is performed as follows. A complete discharge 210 of the SCR catalytic converter 2 is effected, for example, with a less reducing agent solution metered into the exhaust gas line 3 than may be necessary for a complete SCR of nitrogen oxides, whereby possible ammonia is no longer contained in the SCR catalytic converter 2 . This is followed by a determined set mass flow rate of the reducing agent solution having a substoichiometric ratio of, for example, α = 0.5 (

) is metered upstream of the SCR catalytic converter 2 (211).

)의 계산(214)이 실행된다. 계산(214) 동안, 아화학량론적 비율(α) 및 총 배기가스 질량 유량(

)이 고려된다. SCR 촉매 컨버터(2)에서 환원된 질소 산화물은, 실제로 계량 공급되어 SCR 촉매 컨버터(2)에 존재하는 암모니아 환원제의 질량에 직접적으로 좌우된다. 설정 질량 유량(

)과 실제 질량 유량(

)의 비교(215)에 의해 질량 편차(Δm)가 산출된다.Accordingly, the nitrogen oxide concentration (NOxN) downstream of the SCR catalytic converter 2 is detected through the first nitrogen oxide sensor 31 (212), and the nitrogen oxide concentration (NOxV) upstream of the SCR catalytic converter 2 is the second 2 is detected by the nitrogen oxide sensor 32 (213). In still other embodiments, the nitrogen oxide concentration NOxV upstream of the SCR catalytic converter 2 may be modeled, especially if the second nitrogen oxide sensor 32 is not provided upstream of the SCR catalytic converter 2 . The actual mass flow rate (

) is calculated 214 . During calculation 214, the substoichiometric ratio (α) and the total exhaust gas mass flow rate (

) is considered. The nitrogen oxides reduced in the SCR catalytic converter 2 depend directly on the mass of the ammonia reducing agent actually metered in and present in the SCR catalytic converter 2 . Set mass flow (

) and the actual mass flow (

) by comparison 215 of the mass deviation Δm is calculated.

Finally, the mass deviation (Δm) of the reducing agent is compared with a first threshold value (S ₁ ) which in this example can be 25% ( 220 ). If the mass deviation Δm exceeds the first threshold value S ₁ , a defect of the transfer pump 11 is output ( 221 ). This means that, in the pressure control mode DM, a change 205 of the opening period of the metering valve 15 in order to compensate for the pressure defect of the defective transfer pump 11 , the mass deviation Δm of the reducing agent solution metered in is due to the enlargement of Conversely, if the mass deviation Δm is below or equal to the first threshold value S ₁ , a fault of the metering valve 15 is output 222 . Here, the defect of the metering valve 15 due to the change 205 of the opening period of the metering valve 15 is compensated, whereby the mass deviation Δm is reduced.

4 shows a second embodiment of the method according to the invention. The same reference numerals as in FIG. 3 mean that the steps correspond to them, and accordingly, reference is made to the description of FIG. 3 for the description of the reference numerals. In the case of the second embodiment, adaptation of the metering supply by the adaptation factor a is carried out in a known manner. Briefly and clearly, the modeled nitrogen oxide value and the nitrogen oxide value measured by the first nitrogen oxide sensor 31 disposed downstream of the SCR catalytic converter 2 are compared with each other, and an adaptation is made according to this comparison. this is executed After the pressure fault is determined ( 200 ), an adaptation factor (a) is detected (230) and stored (231) as a nominal adaptation factor (a _A ). Since the fault exists in the transfer pump 11 or metering valve 15, the nominal adaptation factor a _A takes an increased or decreased value, eg 1.5 based on the stoichiometric ratio when the mass deviation is 50%. takes the value of In still other embodiments, a point may be provided for determining 200 pressure defects using a comparison of a threshold with an adaptation factor (a) or a nominal adaptation factor (a _A ). This is followed by setting 201 of the fault-tolerant mode FM and changing 205 of the opening period of the metering valve 15 in the same manner as already described in connection with FIG. 3 . As a result, after the pressure control mode DM is set, the adaptation factor a is reset to 1 and a new adaptation is started (233). During the new adaptation, learning 234 of the new adaptation factor a _N over a learning time t _L is performed. Based on the pressure control being implemented, the new adaptation factor a _N takes on a new value different from the nominal adaptation factor. Through comparison 235 of the nominal adaptation factor a _A and the new adaptation factor a _N , an adaptation matching Δa proportional to the mass deviation Δm is calculated.

According to an embodiment, the mass deviation Δm may first be calculated and then compared with a first threshold S ₁ as already described in FIG. 3 (steps 220 to 222) (220). . In the case of the embodiment shown in FIG. 4 , the adaptive matching amount Δa proportional to the mass deviation Δm is compared with the second threshold value S ₂ (240). As a specific example, the second threshold value S ₂ may be 30%. Therefore, if the adaptive matching amount Δa exceeds the second threshold value S ₂ , thereby exceeding 25%, consequently the mass deviation Δm is greater than the first threshold value S ₁ , 241 ) , similarly to FIG. 3 , a defect of the transfer pump 11 is output ( 242 ). If this is not the case, the resulting mass deviation Δm is less than or equal to the first threshold S ₁ (243), and a fault of the metering valve 15 is output similarly to FIG. 3 ( 244).

In Fig. 5 there is shown a graph of the mass deviation Δm and pressure p of the reducing agent solution over time t for a metered feed in which the SCR system 1 is already operated in pressure control mode DM. In the first region 110 , in which the metering valve 15 is closed, the transfer pump 11 delivers the reducing agent solution, whereby the third pressure profile p ₃ is changed from the ambient pressure p _a to the set pressure p p _s ) is reached. Since the metering valve 15 is closed, the reducing agent is not metered into the exhaust gas line 3 , whereby the mass deviation Δm becomes zero. From the "injection starting point" (BIP) the metering valve 15 is opened, and the reducing agent solution is metered into the exhaust gas line 3 . In the second region 111 in which the metering supply is made, the pressure p is continuously adjusted to the set pressure p _s , whereby the third pressure profile p ₃ moves up and down around the set pressure p _s . will go up and down This, as already described earlier, acts on the mass deviation Δm. The first threshold S ₁ is 25% in this region. In the case of this embodiment, the mass deviation Δm rises to exceed the first threshold value S ₁ . Correspondingly, according to the method herein, a fault in the transfer pump 11 is output 221 , 242 . Furthermore, here the learning time t _L is shown as an example. The learning time t _L starts the pressure control at the “injection starting point” (BIP), and can be run of any length in the second region 111 . Also, the learning time may, in other embodiments, continue over several metering feeds.

Claims (10)

A method for diagnosing an SCR system (1) comprising a transfer pump (11) and a metering valve (15), the method comprising:
- determining (200) a pressure defect in the SCR system (1);
- setting the pressure control mode (DM) of the SCR system (1);
- detecting the mass deviation (Δm) of the reducing agent solution;
- outputting (221; 242) a fault to the transfer pump 11 if the mass deviation Δm exceeds the first threshold value S ₁ ;
- outputting (222; 244) a fault to the metering valve (15) if the mass deviation (Δm) is below or equal to a first threshold value (S ₁ ); . Method according to claim 1, characterized in that after a pressure fault is determined (200) in the SCR system, the setting (201) of the fault intrinsic mode (FM) of the SCR system (1) is performed. 3. The method according to claim 2, characterized in that upon setting (201) of the fault-tolerant mode (FM), an engine check light which signals the fault-tolerant mode (FM) of the SCR system (1) is activated (202), Diagnostic method of SCR system. Method according to any one of the preceding claims, characterized in that the setting of the pressure control mode (DM) is realized through a change (205) of the opening period of the metering valve (15). . The diagnostic method of the SCR system according to any one of claims 1 to 3, characterized in that the setting of the pressure control mode is realized through changing the control of the transfer pump. 4. The method according to any one of claims 1 to 3, for detecting the mass deviation (Δm) of the reducing agent solution,
- completely draining (210) the SCR catalytic converter (2) of the SCR system (1);
- at least one set mass flow rate of the reducing agent solution in a substoichiometric ratio α upstream of the SCR catalytic converter 2

) metering supply step (211);
- detecting (212, 213) the nitrogen oxide concentration (NOxN) downstream of the SCR catalytic converter (2) and the nitrogen oxide concentration (NOxV) upstream of the SCR catalytic converter (2);
- substoichiometric ratio (α) and total exhaust gas mass flow rate (

) is considered, the actual mass flow rate of the reducing agent solution (

) calculating 214 ; and
- set mass flow ( ) to calculate the mass deviation (Δm)

) and the actual mass flow (

) comparing (215); 4. The method according to any one of claims 1 to 3, for detecting the mass deviation (Δm) of the reducing agent solution,
- detecting (230) an adaptation factor (a) before the pressure control mode (DM) is set;
- storing 231 the adaptation factor a as a nominal adaptation factor a _A ;
- resetting (232) the adaptation factor (a) after the pressure control mode (DM) is set;
- learning 234 a new adaptation factor a _N during the pressure control mode DM over a learning time t _L ; and
- Comparing (235) the nominal adaptation factor (a _A ) and the new adaptation factor (a _N ) in order to calculate the amount deviation (Δm); A computer program stored on a machine-readable storage medium and configured to execute each step of the method according to any one of claims 1 to 3. A machine-readable storage medium storing the computer program according to claim 8 . An electronic control device (5) configured to carry out a diagnosis of the SCR system (1) using a method according to any one of the preceding claims.

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