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Diagnostic Procedure

WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition switch to ON position. Using Lexus hand-held tester, clear DTCs in occupant classification ECU. See CLEARING PASSENGER OCCUPANT CLASSIFICATION SYSTEM DTCS USING LEXUS HAND-HELD TESTER  under DIAGNOSTICS. Clear DTCs in air bag sensor assembly. See CLEARING DIAGNOSTIC TROUBLE CODES (DTCS)  under DIAGNOSTICS. Turn ignition switch to LOCK position. Turn ignition switch to ON position. Retrieve DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES (DTCS)  under DIAGNOSTICS. If DTC B1781 is retrieved, go to next step. If DTC B1781 is not retrieved, check for intermittent fault. See AIR BAG WARNING LIGHT INTERMITTENT .
  2. Turn ignition switch to LOCK position. Disconnect negative battery cable and wait at least 90 seconds. Access occupant classification ECU. See OCCUPANT CLASSIFICATION ELECTRONIC CONTROL UNIT (ECU)  under REMOVAL & INSTALLATION. Check for proper connection of occupant classification right front sensor and occupant classification ECU connectors. If connectors are properly connected, go to next step. If connectors are not properly connected, connect connectors and go to step  1.
  3. Disconnect occupant classification ECU harness connector O4. Disconnect occupant classification right front sensor connector O6. Connect negative battery cable. Turn ignition switch to ON position. Measure voltage between ground and harness side of occupant classification ECU connector O4, terminal No. 2 (Orange wire, circuit SGD2). See Figure. Measure voltage between ground and harness side of occupant classification ECU connector O4, terminal No. 8 (Blue wire, circuit SIG2). Measure voltage between ground and harness side of occupant classification ECU connector O4, terminal No. 12 (White wire, circuit SVC2). If voltage is more than one volt, repair or replace wire harness between occupant classification ECU and occupant classification right front sensor. If voltage is less than one volt, go to next step.
  4. Turn ignition switch to LOCK position. Wait at least 90 seconds. Connect jumper wire between harness side of occupant classification right front sensor connector O6, terminals No. 1 and 3. See Figure. Connect jumper wire between harness side of occupant classification right front sensor connector O6, terminals No. 2 and 3. Measure resistance between harness side of occupant classification ECU connector O4, terminal No. 2 and 8. Measure resistance between harness side of occupant classification ECU connector O4, terminal No. 2 and 12. If resistance is more than one ohm, repair or replace wire harness between occupant classification ECU and occupant classification right front sensor. If resistance is less than one ohm, go to next step.
  5. Remove jumper wire. Measure resistance between harness side of occupant classification ECU connector O4, terminal No. 2 and 8. Measure resistance between harness side of occupant classification ECU connector O4, terminal No. 2 and 12. Measure resistance between harness side of occupant classification ECU connector O4, terminal No. 8 and 12. If resistance is less than one megohm, repair or replace wire harness between occupant classification ECU and occupant classification right front sensor. If resistance is more than one megohm, go to next step.
  6. Measure resistance between ground and harness side of occupant classification ECU connector O4, terminal No. 2. Measure resistance between ground and harness side of occupant classification ECU connector O4, terminal No. 8. Measure resistance between ground and harness side of occupant classification ECU connector O4, terminal No. 12. If resistance is less than one megohm, repair or replace wire harness between occupant classification ECU and occupant classification right front sensor. If resistance is more than one megohm, go to next step.
  7. Connect occupant classification ECU connector O4 and occupant classification right front sensor connector O6. Connect negative battery cable. Turn ignition switch to ON position. Using Lexus hand-held tester, clear DTCs in occupant classification ECU. Clear DTCs in air bag sensor assembly. Turn ignition switch to LOCK position. Turn ignition switch to ON position. Retrieve DTCs. If DTC B1781 is displayed, go to next step. If DTC B1781 is not displayed, check for intermittent fault.
  8. Turn ignition switch to LOCK position. Wait at least 90 seconds. Replace occupant classification ECU. Perform occupant classification ECU initialization. See OCCUPANT CLASSIFICATION ELECTRONIC CONTROL UNIT (ECU) INITIALIZATION PROCEDURE . If occupant classification ECU initialization is normal, go to next step. If occupant classification ECU initialization is not normal, go to step  10.
  9. Connect negative battery cable. Turn ignition switch to ON position. Using Lexus hand-held tester, clear DTCs in occupant classification ECU. Clear DTCs in air bag sensor assembly. Turn ignition switch to LOCK position. Turn ignition switch to ON position. Retrieve DTCs. If DTC B1781 is displayed, go to next step. If DTC B1781 is not displayed, test is complete.
  10. Turn ignition switch to LOCK position. Wait at least 90 seconds. Replace left front seat adjuster. See FRONT SEAT ADJUSTER FRAME  under REMOVAL & INSTALLATION. Perform occupant classification ECU initialization.
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