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How To Read Diagnostic Information

NOTE: Cruise control testing is not available.
NOTE: When connecting test equipment, disconnect Engine Control Module (ECM) connector "D" first. When reconnecting connectors, connect connector "D" last. See ECM CONNECTOR IDENTIFICATION .

Diagnostic information is located in 6 different categories: FUEL INJECTION SYSTEM TESTS , IGNITION SYSTEM TESTS , ELECTRONIC ACCELERATOR TESTS , CRUISE CONTROL TESTS , FUEL INJECTOR TESTS  and FUEL PUMP TESTS . Additionally DTC DESCRIPTION  is included to further understand DTC diagnosis and/or diagnose intermittent failures. The far left column in testing format in all categories is a numerical step. For reading and understanding fault code diagnosis, as an example, using FUEL INJECTION SYSTEM TESTS, start at step 1.2. Under TEST SCOPE column, component or circuit being tested is voltage supply (circuit 30). Under TEST CONNECTION column, using DVOM, measure voltage between socket box terminal No. 1 and socket box terminal No. 12. Measurement is being made between Data Link Connector (DLC) (X11/4) terminal No. 1 and Engine Control Module (ECM) connector terminal No. 4 on connector "B" as identified by (4B). Manufacturer recommends using Socket Box (129 589 00 21 00) for making measurements to prevent damage to electrical connectors and terminals. See Fig 1. Under TEST CONDITION column, make measurement with ignition on. Voltage is 11-14 volts under NOMINAL VALUE column. If voltage is not within specification, follow instructions under POSSIBLE CAUSE/REMEDY column. Repair or replace wiring as necessary at passenger-side fuse/relay module (K40/4), fuse box (F1) or Base Module (BM) (N16/1). Manufacturer identifies all system components with an alphanumeric identification in testing procedures (i.e., N3/10 is for ECM). See COMPONENT/CIRCUIT IDENTIFICATION .

Fig 1: Connecting Socket Box
G99F08541Courtesy of MERCEDES-BENZ OF NORTH AMERICA.