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Test 4: Tachometer

NOTE: Before changing value on signal generator, turn ignition off.

Disconnect engine control module harness connectors. See Figure . Connect Signal Generator (DTR-8416) between ground and terminal No. 17 at data link connector, according to manufacturer's instructions. See Fig 1 . Set voltage amplitude on signal generator to 10 volts. Turn ignition switch to RUN position. Ensure tachometer reading at each setting of signal generator is as specified. See TACHOMETER TESTING  . If tachometer readings are as specified, check Engine Control Module (ECM) output and repair as necessary. If tachometer readings are not as specified, repair wiring. See WIRING DIAGRAMS  .

TACHOMETER TESTING

Signal Generator Setting (Hz) Tachometer Reading (RPM)
2.2L & 2.3L Engines
30 1000
130 4000
200 6200
2.8L Engines
50 1000
195 4000
315 6400
Fig 1: Identifying Data Link Connector Terminals No. 17 & 30
G97G11938Courtesy of MERCEDES-BENZ OF NORTH AMERICA.