Diagnostic Trouble Code Memory (Section 11)

CAUTION: The DTC readout must be performed on both ignition control modules (N1/4 and N1/5). Possible indicated faults of the left or right control module must be checked with the socket box tester. If the engine does not run, both ignition systems must be checked, one after another, with the socket box tester.

The ignition control modules (N1/4) and N1/5) are equipped with diagnostics, including DTC memory. Malfunctions which occur with the engine running are counted by the receptive malfunction counter. A DTC is recorded into the respective control unit's memory only if the same fault has occurred after 8 sequential engine starts.

This prevents a DTC from being recorded if, for example, it occurred only once. If a fault occurred only 7 times, then the DTC memory will be cleared again after a certain number of engine starts. The DTC memory can be read with the impulse counter scan tool. The memory remains active even if the vehicle's battery is disconnected. A DTC readout 17 (Crankshaft Position Sensor defective) is stored immediately.

Malfunctions can be recalled from memory using the impulse counter scan tool with engine off and ignition ON. DTC's ranging from 1 to 39 may appear on the display of the impulse counter scan tool. See Fig 1 .

Fig 1: Identifying Special Tools (Section 11)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The DTC 1 indicates: No fault recognition in system. All further DTC's refer to a particular malfunction source. If there are multiple system malfunctions, the malfunction assigned with the lowest DTC will be displayed first.

If the DTC indicated first reappears after more than 2 DTC readouts, then no further malfunctions are present in the system. After eliminating all faults, they must be cleared individually.

In case of engine complaints, the DTC memory must be read and the fault must be eliminated before proceeding with any additional repairs.