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Home >> Lexus >> 1992 >> SC 400 >> Repair and Diagnosis >> Accessories & Equipment >> Cruise Control Systems >> Testing >> Code 21 Or 23 Speed Sensor Circuit >> Speedometer/Vehicle Speed (4-Pulse) Signal Check
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Speedometer/Vehicle Speed (4-Pulse) Signal Check

  1. Drive vehicle and check odometer operation. If odometer does not operate, trouble shoot odometer. If odometer operates properly, remove instrument cluster with wiring harness still attached. Go to next step.
  2. Turn ignition on. Connect voltmeter between appropriate instrument cluster connector terminal and ground. See SPEED SIGNAL CHECK TERMINAL IDENTIFICATION  table. See Figure, Figure or Figure . Raise and support vehicle and rotate drive shaft.
    SPEED SIGNAL CHECK TERMINAL IDENTIFICATION

    Application Terminal
    ES300 No. 14 (Connector "B")
    LS400 No. 10 (Connector "A")
    SC300 & SC400 No. 14 (Connector "A")
  3. Voltage should fluctuate between zero volts to 5 volts (or more) per revolution of drive shaft. If voltage does not exist or does not fluctuate as indicated, go to step 5). If voltage fluctuates, go to next step.
  4. Check wiring harness between instrument cluster and cruise control ECU. If speedometer/vehicle speed (4-pulse) signal and wiring harness are okay, check and replace cruise control ECU. If speedometer/vehicle speed (4-pulse) signal and wiring harness are not okay, trouble shoot instrument cluster or repair wiring harness.
  5. On LS400, check instrument cluster power source. On SC300 and SC400, replace circuit plate. On ES300, temporarily install a replacement character plate and retest circuit. If circuit operation is correct, replace character plate. If circuit operation is still incorrect, replace instrument cluster computer.
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