Diagnosable DME Control Unit

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A self-diagnosis feature with fault memory is incorporated into the DME control unit to permit certain faults to be detected and stored.

The DME control unit has a permanent positive connection to prevent deletion of detected and stored faults when the Iginition is switched off. Detected faults remain stored in the fault memory for at least 50 engine starts.


If the DME control unit plug or the battery is disconnected, the fault memory will be cleared. Tester Connections:

The diagnostics socket is located on the right-hand side of the passenger footwell. Note:

The fault path and fault code displayed on the System Tester 9288 will be complemented by the relevant test point in the troubleshooting plan.

The Eprom module Version 4.0 may be used to select the following menus that may in turn be used to select additional submenus. These are displayed by the System Tester in text form.

Selectable menus:

• Input signals

• Knock registration

• Actual values

• Drive link active

This DME diagnosis/troubleshooting plan is based on the contents of the fault memory. Paths not covered by self-diagnosis are diagnosed by conventional means (test points 28 - 33, refer to fault list opposite).

Troubleshooting requires that the person performing the tests

• is familiar with the location of components, function and technical relationships of the systems being tested

• is able to read and evaluate Porsche wiring diagrams

• knows the functions of circuits and relays

• is capable of using testers such as oscilloscope, voltmeter, ohmmeter and ammeter, as well as of evaluating the test results.

The fault text displayed indicates the fault path, i.e. the fault may be present anywhere, from the control unit, across all connectors up to the component itself.

Before reading the fault memory, do not try to locate faults by disconnecting plugs etc., since this may be detected and stored as a fault in the fault memory.

Note for System Tester 9288

If the tester display shows ... not present, this could mean

• Fault did not exist at time of testing

• In case of a loose contact, an additional + symbol is displayed. Example: ... not present +

Remedy: Visual inspection of path

• Conditions under which the fault is tested do not correspond to the conditions under which the fault occurred.

Remedy: Conform with conditions displayed on the tester. If the Signal unplausible message is displayed on the tester, this could mean

• The signal of the monitored component is not within the tolerance range.

Explanations for the counter shown on the tester display

When the fault is detected for the first time, the counter is always set to 50. If a lower number is displayed, determine the difference between 50 and the value shown. This value represents the number determined from the combination of starting process, meeting the test conditions and non-presence of the fault. When the number 0 is reached, the fault path is deleted in the control unit.

Should the fault status change from not present to present at a number below 50, the counter is reset to 50. If a number above 50 is displayed, the difference indicates the number of loose contacts that have occurred. Even at a value above 50, the counter counts down to zero when the above combination of conditions is met.

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