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Home >> Mercedes Benz >> 1996 >> SL320 >> Repair and Diagnosis >> Body & Frame >> Seats >> Seats - Power >> System Tests >> Forward/Rearward Function Inoperative

Forward/Rearward Function Inoperative

  1. Disconnect power seat control module harness connector No. 1. See Figure . Measure resistance between terminals No. 3 and 4 at power seat control module harness connector No. 1. When seat switch is operated to forward position, approximately 42 ohms should exist. When seat switch is operated to rearward position, approximately 16 ohms should exist. When switch is in neutral position, approximately 2200 ohms should exist. If resistance is as specified, go to next step. If resistance is not as specified, check wiring. See WIRING DIAGRAMS  . If wiring is okay, replace power seat switch.
  2. Connect power seat control module harness connector No. 1. Disconnect power seat control module harness connector No. 7. Measure voltage between pins No. 1 and 2 at power seat control module connector No. 7. When seat switch is operated to forward position, battery voltage should exist. When seat switch is operated to rearward position, battery voltage should exist with opposite polarity. When switch is in neutral position, less than one volt should exist. If voltage is as specified, go to next step. If voltage is not as specified, replace power seat control module.
  3. Measure voltage between pins No. 3 and 5 at power seat control module connector No. 7. If approximately 5 volts exists, go to next step. If approximately 5 volts does not exist, replace power seat control module.
  4. Measure voltage between pins No. 4 and 5 at power seat control module connector No. 7. If approximately 5 volts exists, go to next step. If approximately 5 volts does not exist, replace power seat control module.
  5. Measure resistance between terminals No. 4 and 5 at power seat control module connector harness connector No. 7. If approximately 2000 ohms exists, go to next step. If approximately 2000 ohms does not exist, replace forward/rearward motor.
  6. Measure resistance between terminals No. 3 and 5 at power seat control module connector harness connector No. 7 and note value. Measure resistance between terminals No. 3 and 4 at power seat control module connector harness connector No. 7 and note value. If total of both values obtained is 2000-2400 ohms, go to next step. If total of both values obtained is not 2000-2400 ohms, replace forward/rearward motor.
  7. Measure resistance between terminals No. 1 and 2 at power seat control module connector harness connector No. 7. If .5-1.5 ohms exists, system is okay at this time. If .5-1.5 ohms does not exist, replace forward/rearward motor.
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