Diagnostic method for motor vehicles for checking electronically controlled systems

A diagnostic method for motor vehicles with a diagnostic device for checking electronically controlled systems, in which a fault memory provided in an electronic control device is interrogated and in which test steps to be performed in accordance with the information in the fault memory are prescribed. The test steps performed in response to the prescribed test steps are recorded in the electronic control device.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a diagnostic method for motor vehicles 
with a diagnostic device for checking electronically controlled systems, 
in which a fault memory provided in an electronic control device is 
interrogated and in which test steps to be performed are prescribed. 
A diagnostic method for motor vehicles with a diagnostic device for 
checking an electronically controlled system, in which a fault memory 
provided in an electronic control device is interrogated, is known for 
example from German Patent Document DE 34 37 980 A1. In this known method, 
a device is provided with which, for diagnosis, the microcomputer of an 
electronic control device is replaced by a diagnostic microcomputer 
pluggable into a plug-in connection, this diagnostic microcomputer 
comprising, in addition to diagnostic functions, the functions of the 
microcomputer installed as standard equipment. Recognized faults or 
malfunctions are stored in a fault memory in the control device and can be 
transferred, preferably in the maintenance facility, through a connection 
on the diagnostic microcomputer to an external evaluating device. 
External evaluating devices in practice are designed for example so that 
not only the information to be obtained from the fault memory but also 
test steps to be performed in accordance with this information are 
displayed for accurate troubleshooting. As indicated for example in German 
Patent Document DE 41 18 692 A1, the fault memory for example displays a 
fault number, the type of fault, and operating parameters that exist when 
the fault occurs. The type of fault can be for example a short circuit to 
ground, a short circuit to the positive pole, or a break. The fault number 
indicates for example which component or electrical path is defective. 
Such a fault number however is only a functional item of fault information 
that delimits the location of the fault but cannot pinpoint it. 
One possible item of fault information is the lack of a certain sensor 
signal. This fault can be attributed to several possible causes, however: 
for example a break at any point in the cable harness or an incompletely 
inserted plug or a defective input circuit in the control device 
associated with this sensor signal. 
The test steps prescribed on the basis of fault information therefore serve 
to locate the exact cause of the fault. Since in practice the components 
associated with a specific fault, especially electronic control devices, 
are exchanged arbitrarily without performing the test steps, unnecessarily 
high repair costs result. In addition, components are sent for repair 
which are actually intact. 
An object of the present invention is to monitor function and fault checks 
during diagnostic procedures, especially in the maintenance facility, and 
to ensure a correct function and fault check. 
This and other objects are achieved by the present invention which provides 
a diagnostic method for motor vehicles with a diagnostic device for 
checking electronically controlled systems having an electronic control 
device with a fault memory and prescribed test steps. This method includes 
the steps of interrogating the fault memory provided in the electronic 
control device, and at least partially recording test steps actually 
performed in response to the prescribed test steps. 
The test steps which a garage mechanic for example performs after receiving 
the test steps to be performed, are at least partially handled by the 
diagnostic device or control device. In certain embodiments, these test 
steps, once performed, are stored in the diagnostic device and/or in the 
control device. 
This procedure according to the invention provides a documentation of the 
test steps performed. This documentation can be used in different ways. 
The mere fact that a garage mechanic knows that the test steps he 
performed can be checked motivates him to perform correct functional and 
fault checking. This results in an elimination of the real and not just 
suspected faults, so that the availability of the electronically 
controlled system is increased. 
In certain embodiments of the method of the present invention, the test 
steps recorded are not merely stored in any form, but in the chronological 
sequence in which they were performed. This additional documentation on 
the chronological sequence of the test steps performed serves to check 
whether the fault check was properly performed. For example a component 
should not be replaced before a search for the fault has been performed. 
It is also logical not to erase the fault memory until the fault has been 
eliminated. 
In certain embodiments, the test steps included are compared in the control 
device or in the diagnostic device with at least a selection of the test 
steps to be performed. One possible selection, for example, is directed at 
determining whether the most important test steps for determining the 
cause of a fault have been performed. 
In this way, a determination is made automatically by the control device or 
diagnostic device as to whether a correct fault check has taken place. On 
the basis of this automatic comparison, automatic reactions on the part of 
the control device or the diagnostic device are also possible on the basis 
of the results of the comparison. 
Certain embodiments account for the possible result of automatic comparison 
that indicates a test step to be performed is not included in the test 
steps presented. Then a message corresponding to this information is 
displayed and/or stored. Preferably this message is displayed on the 
diagnostic device and stored in the control device. 
As a result of this automatic display or storage of only one item of 
information, monitoring the function check is simplified. 
Another possible result of automatic comparison is the information that the 
test steps presented differ in their sequence from the sequence of the 
test steps to be performed. In this case a message likewise corresponding 
to this information to displayed and/or stored, according to certain 
embodiments of the invention. Storage takes place in the control device 
and display takes place on the diagnostic device in preferred embodiments. 
A message according to the above described embodiment may include an 
instruction to repeat the test steps, a warning that the test steps to be 
performed do not agree with the prescribed test steps, or an indication of 
which test steps have not been performed, among others. 
In certain embodiments of the invention, the test steps that have been 
performed and included and/or any messages are stored in a nonvolatile 
form in the control device to be monitored. EEPROMs are preferably used 
for nonvolatile storage. 
This design according to the invention serves in particular to make sure 
that even a control device that has been unplugged from the power supply 
and sent for repair can be monitored to determine whether an arbitrary 
replacement of the control device was performed or whether faults in the 
other components were ruled out as the cause of the stored fault. 
If the anticipated effect occurs as a result of diagnostic method according 
to the invention, considerable repair costs are saved. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
The drawing contains a control device SG and a diagnostic device DG. A 
bidirectional line is provided between control device SG and diagnostic 
device DG for example to exchange data. Both the control device SG and the 
diagnostic device DG are microprocessor-controlled and contain computers 
not shown here. In addition, the control device SG contains a fault memory 
FS, in which for example the type of fault, fault location, and fault 
frequency are stored when faults occur in the system associated with this 
control device SG corresponding to a known fault recognition program. For 
example, in the garage, using diagnostic control device DG, this fault 
memory FS is read out and displayed via a display, not shown here, of 
diagnostic device DG. 
Diagnostic device DG contains an allocation memory ZS in which a separate 
test plan (Plan 1, Plan 2, Plan 3, . . . ) is assigned to every fault that 
appears (Fault 1, Fault 2, Fault 3, . . . ). In addition, test plan 
memories PPS1, PPS2 are provided in the diagnostic device in which the 
test steps prescribed for each test plan (Test Step 1, Test Step 2, . . . 
) are stored corresponding to a predetermined sequence. For example, Plan 
1 provides eight test steps which a garage mechanic must perform in 
sequence. The prescribed test plan is either already known by control 
device SG or is transmitted to control device SG and stored in a 
prescribed test plan memory VPS. In addition, a real-time test plan memory 
(APS) is provided in control device SG in which the actual test steps 
performed by the garage mechanic are recorded and stored. The prescribed 
test plan memory VPS and the real-time test plan memory APS are preferably 
nonvolatile memories. As a result, their contents can be interrogated and 
compared by diagnostic device DG even when control device SG is unplugged. 
However, it is also possible for control device SG itself to compare the 
two memory contents for example and to store the information in its own 
memory (not shown here) as to whether the memory contents are identical or 
not. In this case it is possible to use the diagnostic device DG to call 
up only this message when exact documentation of the actual test steps 
performed is not required. If diagnostic device DG determines that the 
contents of the prescribed test plan memory VPS and the real-time test 
plan memory APS do not match, a display on the diagnostic device calling 
for repetition of the prescribed test step is possible. 
The following is an example of the use of the diagnostic method according 
to the invention depending on the contents of the fault memory of a motor 
control device: 
A garage mechanic uses the diagnostic device (DG) to read the fault memory 
(FS) the fault message "injection valve 1 short circuit to ground" has 
been stored. The diagnostic device (DG), on the basic of this fault 
message, prescribes the following test plan for the garage mechanic by 
allocation memory (ZS): 
1. shut off engine 
2. operate injection valve 1 
3. check leads to injection valve and replace if defective 
4. replace injection valve if leads are in order 
5. delete fault memory 
These five test steps must performed in the sequence given. If the garage 
mechanic in fact only does the following: 
1. replaces injection valves 
2. deletes the fault memory only test steps 4 and 5 will be stored in the 
real-time test plan memory (APS), and it can then be determined that test 
steps 1 to 3 were not performed. If this improper procedure on the part of 
the garage mechanic is discovered, the garage mechanic can be instructed 
for example to perform the prescribed test plan again, for example using 
the diagnostic device (DG). If an improper procedure is discovered, any 
number of measures are possible in order to motivate the garage mechanic 
to follow the prescribed test plan when repeating the test steps. 
By using nonvolatile memories, an improper procedure in performing the test 
steps can be discovered even when the control device (SG) is unplugged, so 
that arbitrary replacement of components without performance of the test 
steps is prevented. 
In addition, the availability of electronically-controlled systems is 
increased by eliminating only actual and not suspected defects. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.