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Home >> Lexus >> 1991 >> ES 250 Standard >> Repair and Diagnosis >> Accessories & Equipment >> Cruise Control Systems >> Circuit Testing >> Procedure F, Speed Sensor Circuit (Instrument Cluster)

Procedure F, Speed Sensor Circuit (Instrument Cluster)

  1. Speedometer Cable:  If speedometer needle fluctuates when driving at a steady speed, replace faulty speedometer cable. If speedometer needle does not fluctuate, ensure ignition switch is off and go to next step.
  2. Speed Sensor:  Disconnect instrument cluster connector. Check continuity between wiring harness side of speed sensor terminal B3 and ground. See Figure. If continuity exists, go to next step. If no continuity exists, repair open circuit in wire harness between terminal No. B3 and ground.
  3. Check speed sensor operation. See SPEED SENSOR TEST  under TESTING. If speed sensor is faulty, replace sensor and recheck cruise control system. If speed sensor is okay, go to next step.
  4. Turn ignition on. Check for 5-volt reference voltage between ECU terminal No. 8 and ground. If voltage is correct, go to next step. If voltage is incorrect, power source or ECU is faulty. Recheck power source circuit. See PROCEDURE A, POWER SOURCE CIRCUIT  under TROUBLE SHOOTING.
  5. Check for 5-volt reference voltage between wiring harness side of speed sensor terminal B10 and ground. If voltage is correct, turn ignition off and go to next step. If voltage is incorrect, repair short circuit in wire harness between speed sensor terminal B10 and ECU terminal No. 8.
  6. Cruise Control ECU:  Disconnect ECU. Check continuity between wiring harness side of speed sensor terminal B10 and wiring harness side of ECU terminal No. 8. If continuity exists, replace faulty ECU and recheck cruise control system. If no continuity exists, repair open circuit in wire harness between speed sensor terminal B10 and ECU terminal No. 8.
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