hereafter , a plurality of embodiments of a solenoid valve fault detecting device concerning the present invention will be explained by way of the accompanying drawings . first , a first embodiment of the present invention will be explained by way of fig2 . the same components are denoted by the same numerals in fig1 and 2 . thus , an explanation of the components already mentioned in relation to fig1 will be omitted . in fig2 the numeral 20 denotes a test electric power supply ; 21 is a current limiting resistor having a high resistance whose one end is connected to the test electric power supply 20 ; 22 is a diode whose anode terminal and cathode terminal are connected , respectively , to the other end of the current limiting resistor 21 and the electric power supply line 10 of the solenoid valve coil 3 having first and second coil ends ; p6 is an analog input port of the microcomputer 7 . more specifically , an output from the test electric power supply 20 is supplied to the electric power supply line 10 of the solenoid valve coil 3 via a series circuit consisting of the current limiting resistor 21 and the diode 22 . the test electric power supply 20 , the current limiting resistor 21 and the diode 22 comprise a test electric power supply system . since the output voltage from the test electric power supply 20 is set to be smaller than the output voltage from the battery 1 and diode 22 is connected under the condition of the aforementioned polarity , the output from the battery 1 is supplied to the electric power supply line 10 when the relay 2 is closed . on the other hand , when the relay 2 is open , the diode 22 is conducting electricity and thus , the output from the test electric power supply 20 is supplied to three electric power supply line 10 . in this case , a micro test current not sufficient to drive the solenoid valve is supplied to the solenoid valve coil 3 because the current limiting resistor 21 is designed to have a high resistance . when the battery power supply line 9 , relay 2 , electric power supply line 10 and grounding line 11 of the solenoid valve coil connecting line and switching fet 4 are operating normally , the following signal is inputted into the analog input port p6 of the microcomputer 7 . specifically , when the relay 2 is turned off ( opened ) by the signal supplied to the relay drive circuit 5 from the digital output port p1 of the microcomputer 7 and the switching fet 4 is turned off by the signal supplied to the fet drive circuit 6 from the digital output port p2 of the microcomputer 7 , the test current is supplied to the solenoid valve coil 3 from the test electric power supply 20 via the diode 22 and the current limiting resistor 21 . in this case , a signal of a voltage obtained by dividing an output voltage from the test electric power supply 20 by the current limiting resistor 21 , and a series resistance value of the resistor 8a and the resistor 8b , is inputted into the analog input port p6 of the microcomputer 7 . since the current limiting resistor 21 , the resistor 8a or the resistor 8b has a high resistance in this state , a current sufficient to drive the solenoid valve does not flow in the solenoid valve coil 3 and therefore , the solenoid valve is not actuated . when the relay 2 is turned on ( in the conducting state ) by the output signal from the digital output port p1 of the microcomputer 7 , the diode 22 is cut off and the output voltage from the battery 1 is supplied to the electric power supply line 10 . thus , into the analog input port p6 of the microcomputer 7 is inputted a signal of a voltage obtained by dividing the output voltage from the battery 1 by the resistance - type potential divider 8 . since the resistors 8a and 8b have a high resistance , the solenoid valve is not actuated . also , the current flow from the battery 1 to the test electric power supply 20 is deterred by the diode 22 . if the switching fet 4 is turned on by the output signal from the digital output port p2 of the microcomputer 7 after the relay 2 is turned on as mentioned above , an electric current sufficient to drive the solenoid valve flows from the battery 1 into the solenoid valve coil 3 while a signal of almost zero potential is supplied to the analog input port p6 of the microcomputer 7 . further , when the output signal from the digital output port p1 turns off the relay 2 while the output signal from the digital output port p2 turns on the fet 4 , a signal of zero potential is supplied to the analog input port p6 of the microcomputer 7 . next , when a fault such as 2 short circuit , grounding , etc ., occurs in the battery power supply line 9 , relay 2 , electric power supply line 10 and grounding line 11 of the solenoid valve coil connecting line or switching fet 4 , a signal of the following voltage is supplied to the analog input port p6 of the microcomputer 7 . for example , if a fault such as grounding or disconnection of the electric power supply line 10 or the grounding line 11 occurs , a signal of zero potential is supplied to the analog input port p6 of the microcomputer 7 , irrespective of the output signals from the digital output ports p1 and p2 of the microcomputer 7 . still further , when a fault which prevents the switching fet 4 from being turned on occurs due to a failure of the fet drive circuit 6 or the switching fet 4 , a signal of non - zero potential , that is a signal of a voltage obtained by dividing the output voltage from the test electric power supply 20 by the current limiting resistor 21 and the resistance - type potential divider 8 is inputted into the analog input port p6 of the microcomputer 7 despite the fact that the output signal from the digital output port p1 turned off the relay 2 and the output signal from the digital output port p2 turned on the switching fet 4 . specifically , the microcomputer 7 is able to detect , on the basis of the output voltage from the test electric power supply 20 , a fault causing grounding or disconnection of the electric power supply line 10 or the grounding line 11 before the relay 2 is turned on by the output signal from the digital output port p1 . on the other hand , when a fault which prevents the relay 2 from being turned on occurs due to disconnection of the battery power supply line 9 or a failure in the relay drive circuit 5 or the relay 2 , a signal of a voltage obtained by dividing the output voltage from the test electric power supply 20 by the current limiting resistor 21 and the resistors 8a and 8b constituting the resistance - type potential divider 8 , is inputted into the analog input port p6 of the microcomputer 7 despite the fact that the output signal from the digital output port p1 of the microcomputer 7 turned on the relay 2 and the output signal from the digital output port p2 of the microcomputer 7 turned off the switching fet 4 . thus , the microcomputer 7 is able to detect a fault in the battery power supply line 9 or the relay 2 . in this case , the fault is detected by supplying the output from the battery 1 to the electric power supply line 10 with the relay 2 being turned on by the output signal from the digital output port p1 of the microcomputer 7 . however , by prohibiting the relay 2 from being turned on based on the aforementioned detecting operation , it is possible to avoid damage to components caused by a heavy current when the relay 2 is turned on . a plurality of solenoid valves are installed in an electronic control device for a vehicle so as to control each part of the vehicle . the plurality of solenoid valves are also able to accurately detect a fault in feeding systems for solenoid valve coils by the same means as described above with respect to the single solenoid valve . next , a second embodiment of the present invention will be explained by way of fig3 . according to the second embodiment , the test electric power supply system consisting of the test electric power supply 20 , the current limiting resistor 21 and the diode 22 is connected to the grounding line 11 of the solenoid valve coil 3 , and the signal of the electric power supply line 10 of the solenoid valve coil 3 is inputted into the analog input port p6 of the microcomputer 7 via the resistance - type potential divider 8 , apart from which the configuration of the second embodiment is the same as that of the first embodiment . in other words , the cathode terminal of the diode 22 is connected to the grounding line 11 to supply the test current , whereas the signal of the electric power supply line 10 is divided by the resistors 8a and 8b to be inputted into the analog input port p6 . the second embodiment having the above - described configuration is also able to detect a fault in the battery power supply line 9 , the relay 2 , the electric power supply line 10 , the grounding line 11 or the switching fet 4 on the basis of the electric current supplied by the test electric power supply system in the same manner as mentioned with respect to the first embodiment . further , as for other solenoid valves not indicated in the drawing , a fault in the valves can also be detected in the same manner as mentioned with respect to the first embodiment . next , a third embodiment of the present invention will be explained by way of fig4 . according to the third embodiment , as is indicated in the drawing , a voltage is supplied from a digital output port p4 of the microcomputer 7 instead of from the test electric power supply 20 , and a zener diode 23 is connected between a digital input port p5 of the microcomputer 7 and a grounding point ( gnd ) under a polarity being such that a cathode of the diode 23 is connected to the digital input port p5 whereas an anode of the diode 23 is connected to the grounding point ( gnd ). a clamp voltage of the zener diode 23 is set in such a way as to be recognized to be of a &# 34 ; h &# 34 ; ( high ) level by the microcomputer 7 . since the electric current to be supplied from a test power supply system to feeding system for the solenoid valve coil 3 may be a micro current not sufficient to drive the solenoid valve , it is possible to supply the test current from the digital output port p4 . by inserting the zener diode 23 as mentioned above , an abnormally high voltage is prevented from being applied to the digital input port p5 . when the battery power supply line 9 , relay 2 , electric power supply line 10 and grounding line 11 of the solenoid valve coil connecting line , and switching fet 4 are operating normally , the following signal is inputted into the digital input port p5 of the microcomputer 7 . specifically , before the electric current flows into the solenoid valve coil 3 , the relay 2 is turned off by an output signal from a digital output port p1 of the microcomputer 7 while the switching fet 4 is turned off by an output signal from a digital output port p2 of the microcomputer 7 , and an output signal from the digital output port p4 of the microcomputer 7 is supplied to the electric power supply line 10 via the current limiting resistor 21 and the diode 22 . for example , if a &# 34 ; h &# 34 ; ( high ) level signal is outputted from the digital output port p4 , a voltage which is recognized to be of a &# 34 ; h &# 34 ; ( high ) level by the microcomputer 7 is inputted to the digital input port p5 by the resistance - type potential divider 8 which sets a dividing ratio to be high . if a &# 34 ; l &# 34 ; ( low ) level signal is outputted from the digital output port p4 in the same state as described above , a &# 34 ; l &# 34 ; ( low ) level signal is inputted to the digital input port p5 . when the relay . 2 is turned on by the output signal from the digital output port p1 of the microcomputer 7 in order to prepare an electric current to flow into the solenoid valve coil 3 , a potential of the electric power supply line 10 becomes an output voltage from the battery 1 and thus , the diode 22 is cut off , whereby the supply of an electric current to the solenoid valve coil 3 is cut off , regardless of a level of the signal outputted from the digital output port p4 of the microcomputer 7 . at this time , a voltage clamped by the zener diode 23 is applied to the digital input port p5 of the microcomputer 7 . specifically , a voltage which is recognized to be of a &# 34 ; h &# 34 ; ( high ) level by the microcomputer 7 is inputted to the digital input port p5 . by turning on the switching fet 4 by the output signal from the digital output port p2 after the relay 2 is turned on by an output signal from the digital output port p1 of the microcomputer 7 , an electric current flows into the solenoid valve coil 3 , whereby the grounding line is grounded and thus , a &# 34 ; l &# 34 ; ( low ) level signal is inputted to the digital input port p5 of the microcomputer 7 . further , if the relay 2 is turned off by an output signal from the digital output port p1 of the microcomputer 7 and the switching fet 4 is turned on by an output signal from the digital output port p2 of the microcomputer 7 , a &# 34 ; l &# 34 ; ( low ) level signal is inputted to the digital input port p5 of the microcomputer 7 , regardless of a level of an output signal from the digital output port p4 of the microcomputer 7 . on the other hand , when a fault is occurring in the battery power supply line 9 , the relay , 2 , the electric power supply line 10 and the grounding line 11 of the solenoid valve coil connecting line or the switching fet 4 , a signal of the following level is inputted to the digital input port p5 . specifically , when such a fault as a short - circuiting of the electric power supply line 10 or the grounding line 11 occurs , a &# 34 ; h &# 34 ; ( high ) level signal is inputted to the digital input port p5 of the microcomputer 7 in the same way as it is during normal operation . however , when the output signal from the digital output port p4 is a &# 34 ; l &# 34 ; ( low ) level signal , a &# 34 ; h &# 34 ; ( high ) level signal is inputted unlike in a normal operation case . when such a fault as grounding or disconnecting of the electric power supply line 10 or the grounding line 11 occurs , a &# 34 ; l &# 34 ; ( low ) level signal is inputted to the digital input port p5 unlike the normal operation case if an output signal from the digital output port p4 of the microcomputer 7 is a &# 34 ; h &# 34 ; ( high ) level signal . further , when a fault which prevents the switching fet 4 from being turned on due to a failure in the fet drive circuit 6 or the switching fet 4 occurs , a &# 34 ; h &# 34 ; ( high ) level signal is inputted to the digital input port p5 unlike the normal operation case despite the fact that the digital output port p1 and the digital output port p2 of the microcomputer 7 are outputting a signal for turning off the relay 2 and a signal for turning on the switching fet 4 , respectively , and the digital output port p4 is outputting a &# 34 ; h &# 34 ; ( high ) level signal . as is explained above , the microcomputer 7 is able to detect , on the basis of the level of the signal inputted into the digital input port 5 , a fault occurring in the electric power supply line 10 or the grounding line 11 of the solenoid valve coil connecting line or the switching fet 4 before the relay 2 is turned on by the output signal from the digital output port p1 . when a fault which prevents the relay 2 from being turned on due to disconnection of the battery electric power supply line 9 or failure in the relay drive circuit 5 or relay 2 occurs , a &# 34 ; l &# 34 ; ( low ) level signal is inputted to the digital input port p5 of the microcomputer 7 unlike the normal operation case despite the fact that the digital output port p1 is outputting a signal for turning on the really 2 and the digital output port p2 of the microcomputer 7 is outputting a signal for turning off the switching fet 4 and further , the digital output port p4 of the microcomputer 7 is outputting a &# 34 ; l &# 34 ; ( low ) level signal . thereby , the microcomputer 7 is able to detect a fault occurring in the battery power supply line 9 or the relay 2 . the relay 2 must be turned on to detect such a fault as mentioned above . however , by prohibiting the relay 2 from being turned on based on the aforementioned detecting operation , it is possible to avoid incurring damage to each component as a result of a heavy current when the relay 2 is turned on . as for the other solenoid valves not indicated in the drawing , a fault in the valves can be detected by the same means as described above . next , a fourth embodiment of the present invention will be explained in reference to the circuit indicated in fig5 . according to the fourth embodiment , as is indicated in fig5 the test electric power supply system is connected to the grounding line 11 of the solenoid valve coil 3 and the electric power supply line 10 of the solenoid valve coil 3 is connected to the digital input port p5 of the microcomputer 7 via the resistance - type potential divider 8 and the zener diode 23 , apart from which the configuration of the fourth embodiment is the same as that of the third embodiment . specifically , according to the fourth embodiment , the cathode terminal of the diode 22 is connected to the grounding line 11 to thereby supply to the grounding line 11 the test current supplied from the digital output port p4 of the microcomputer 7 via the current limiting resistor 21 , while the signal of the electric power supply line 10 is inputted to the digital input port p5 via the resistor 8a and 8b and the zener diode 23 . given the above - described configuration , the fourth embodiment is also able to detect , on the basis of the test current supplied from the digital output port p4 of the microcomputer 7 via the lest power supply system , a fault in the battery power supply line 9 , the relay 2 , the electric power supply line 10 , the grounding line 11 or the switching fet 4 . as for solenoid valves not indicated in the drawing , a fault in the valves can be also detected through the same procedure as mentioned in relation to the fourth embodiment . next , a fifth embodiment of the present invention will be explained in reference to the circuit described in fig6 . the aforementioned first through fourth embodiments are not intended to detect a short circuit of both ends of the solenoid valve coil 3 . however , the fifth embodiment is intended for detection of a change in a micro potential difference between the ends of the solenoid valve coil 3 when they are short - circuited . as is indicated in fig6 the fifth embodiment of the present invention has a configuration wherein a differential amplifier circuit 24 for amplifying a potential difference between the ends of the solenoid valve coil 3 is added to the circuit of the first embodiment . therefore , the same components are denoted by the same numerals in fig2 and 6 , and an explanation of the components appealing in both fig2 and fig6 will be omitted here . as is indicated in fig6 the differential amplifier circuit 24 consists ofan operational amplifier 24a , a resistor 24b having a high resistance which is disposed between a positive - phase input terminal (+) of the operational amplifier 24a and the electric power supply line 10 , a resistor 24c having a high resistance which is disposed between the said positive - phase input terminal (+) and a grounding point , a resistor 24d having a high resistance which is disposed between the negative - phase input terminal (-) and the grounding line 11 , a resistor 24e having a high resistance which is disposed between the negative - phase input terminal (-) and an output terminal of the operational amplifier 24a ( that is the analog input port p6 of the microcomputer 7 ) and a zener diode 24f which is disposed between the positive - phase input terminal (+) and the negative - phase input terminal (-) with a polarity such that a cathode terminal of the diode 24f is connected to the positive - phase input terminal (+). the zener diode 24f is interposed between the positive - phase input terminal (+) and the negative - phase terminal (-) in order to protect the operational amplifier 24a . in passing a current into the solenoid valve coil 3 according to the device for detecting a fault in the solenoid valve , the relay 2 is first turned on by an output signal from the digital output port p1 of the microcomputer 7 and then , the switching fet 4 is turned on , whereby a drive current is supplied from the battery 1 to the solenoid valve coil 3 . on the other hand , when not actuating the solenoid valve , the relay 2 is turned off by the output signal from the digital output port p1 and the switching fet 4 is also turned off by the output signal from the digital output port p2 , whereby the drive current from the battery 1 to the solenoid valve coil 3 is cut off and a test current is supplied from the test electric power supply 20 to the solenoid valve coil 3 . since the switching fet 4 is off in this case , the test current does not run and as a result , the voltage at each end of the solenoid valve coil 3 becomes equal and an output voltage from the differential amplifier circuit 24 which becomes about &# 34 ; ov &# 34 ; ( volt ). then , when the operating slate of the switching fet 4 changes from off to on due to the output signal from the digital output port p2 , the test current runs to the grounding point via the solenoid valve coil 3 through the current limiting resistor 21 and diode 22 . when the solenoid valve coil 3 and a current - carrying path of the test current are normal , a potential difference arises between the ends of the solenoid valve coil 3 and therefore , the output voltage from the differential amplifier circuit 24 corresponds to an amplification factor set in accordance with each resistance value of the resistors 24b ˜ 24e . while the voltage signal is being inputted to the analog input port p6 , the microcomputer 7 determines that the solenoid valve coil 3 and its path ( consisting of the electric power supply line 10 , the grounding line 1 land the switching fet 4 ) are normal . however , if the solenoid valve coil 3 is short - circuited in this state , the voltage at each end of the solenoid valve coil 3 becomes equal and thus , the output voltage from the differential amplifier circuit 24 becomes almost ov even though the switching fet 4 is turned on . the microcomputer 7 determines that the solenoid valve coil 3 is short - circuited when the output voltage from the differential amplifier circuit 24 turns out to be &# 34 ; ov &# 34 ; in this state , that is when the level of the signal inputted to the analog input port p6 is &# 34 ; ov &# 34 ;. thus , the microcomputer7 is able to detect a short circuit fault in the solenoid valve coil 3 . by prohibiting the relay 2 and switching fet 4 from being turned on based on the aforementioned detection operation , it is possible to avoid incurring damage to each component as a result of a heavy current when the relay 2 and the switching fet 4 are turned on simultaneously . as for a plurality of solenoid valves not indicated in the drawing , a fault in the valves can be detected by the same means as described above . in the present fifth embodiment , the digital output port p4 of the microcomputer 7 may be used as the supply source of the test current instead of the test current supply 20 as in the third and fourth embodiments . although the invention has been described with respect to particular embodiments , it is to be understood that these embodiments are merely illustrative of the principles of the invention . numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention .