There is a new addition to the BMW Service Tester, the $28,000 gadget built by Sun that attaches to the diagnostic plug under the hood. This addition is a $10,500 device called a Diagnostic Module, which is really a computer with micro-floppy disk drives (the type used with the Apple Macintosh com­ puter). For output display, it uses the CRT screen already in the Service Tes­ ter. There will be one micro-floppy for each model and year of car. The first car to make use of the Diagnostic Module is the new 735i.

The way the Service Tester interacts with the car is quite interesting. On the car there is (can you believe it?) a local area network, consisting of a twisted pair of wires between all computers and control units and terminating in the diagnostic plug. The Service Tes­ter, with its computer, joins this net­ work when it is plugged in.

What can the Service Tester compu­ter do on the network is the question. It can first of all make a call over the network to each of the car’s computers to see which ones are there and work­ ing. One particular car will not have all possible computers on it. For example, our American 735i models will have a climate control computer (i.e. air­ conditioner), but not a heater compu­ ter since the heating and air-conditioner are one unit. Second, it can ask each computer what faults it has found. Most of the computers record the occurrence and the number of each type of fault since the last service was done. Some even record under what conditions the fault occurred, such as engine RPM, temperature, etc. In this way, intermittent faults on the car can be diagnosed and (hopefully) corrected even if the fault can not be reproduced while the car is in for service. Third, when the service technician has fixed a fault (it isn’t clear you can call him mechanic anymore) he can erase the fault memory of the computer detect­ ing the faults in preparation for the next service interval.

Some computers do not record occurrence of faults, such as the instrument cluster computer. However, they and others can do some pretty smart things to help diagnose the cause of a problem. For example, suppose a power window doesn’t work. The first thing the Service Tester computer can do to help is to display the status of the power window switch. It gets this information off of the computer net­ work, independent of the computer that controls the window, which in this case is the ZK E computer. Ifthe switch input to ZKE looks good, one can look at the output. We can see if ZK E has understood the input signals and is outputting a signal to raise or lower the window. We can simulate ZK E’s out­ put signal from the Service Tester to see if the window motors work even if ZK E is down. Let me tell you, its really weird to see the car’s wind ows go up and d own after punching buttons on the Service Tester. And worse yet, you better watch where you are standing before asking the Service Tester to turn on the windshield washers.

The system seems to be very well thought out. Modern computer elec­ tronics are services in similar fashion. But as with modern computers, repairs are not really made in the field, instead whole modules are replaced. Thus, if a problem is caused by a module like ZKE, you’re probably going to pay for a new ZK E, unless it is still covered by the 3 year / 36,000 mile warranty. Another trend in computer repair is remote diagnosis via a modem (com­ puter network interface to telephone lines). I can see that the next step is that someone from Montvale, NJ tells you what is wrong with your disabled BMW sitting next to a phone booth in Bar­ stow. Don’t Jaugh, the new 7 is already pre-wired for cellular phone, so it might not even be necessary to find a phone booth.

-Paul Kunz
Golden Gate Chapter

This article was originally published in the November 1988 edition of Zundfolge