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Home >> Toyota >> 2001 >> Sienna CE >> Repair and Diagnosis >> External Pages >> Different car >> Section 269 (Air Bag Restraint Systems) >> Diagnostic Tests >> DTC B1790: Air Bag Sensor Assembly Communication Circuit Malfunction >> Diagnostic Procedure

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. Clear DTCs in air bag sensor assembly. See CLEARING DIAGNOSTIC TROUBLE CODES (DTCS)  under DIAGNOSTICS. 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. Turn ignition switch to LOCK position. Turn ignition switch to ON position. Retrieve DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES (DTCS)  under DIAGNOSTICS. If DTC B1790 is retrieved, go to next step. If DTC B1790 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. Access air bag sensor assembly. See AIR BAG SENSOR ASSEMBLY  under REMOVAL & INSTALLATION. Check for proper connection of air bag sensor assembly 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. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Disconnect occupant classification ECU connector O4. Disconnect air bag sensor assembly connector A31. Connect negative battery cable. Turn ignition switch to ON position. Measure voltage between ground and harness side of air bag sensor assembly connector A32, terminal No. 16 (Green wire, circuit No. FSP+). Measure voltage between ground and harness side of air bag sensor assembly connector A32, terminal No. 24 (Green/Black wire, circuit No. FSP-). If voltage is less than one volt, go to next step. If voltage is more than one volt, go to step  10.
  4. Turn ignition switch to LOCK position. Disconnect negative battery cable. Wait at least 90 seconds. Connect jumper wire between harness side of occupant classification ECU connector O4, terminal No. 4 (Yellow wire) and No. 8 (Blue wire). See Figure. Measure resistance between harness side of air bag sensor assembly connector A31, terminals No. 16 and 24. If resistance is less than on ohm, go to next step. If resistance is more than one ohm, go to step  11.
  5. Remove jumper wire. Measure resistance between harness side of air bag sensor assembly connector A31, terminals No. 16 and 24. If resistance is more than one megohm, go to next step. If resistance is less than one megohm, go to step  12.
  6. Measure resistance between ground and harness side of air bag sensor assembly connector A31, terminal No. 16. Measure resistance between ground and harness side of air bag sensor assembly connector A31, terminal No. 24. If resistance is more than one megohm, go to next step. If resistance is less than one megohm, go to step  13.
  7. Connect air bag sensor assembly and occupant classification ECU connectors. 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 B1790 is retrieved, go to next step. If DTC B1790 is not retrieved, check for intermittent fault. See AIR BAG WARNING LIGHT INTERMITTENT .
  8. Turn ignition switch to LOCK position. Disconnect negative battery cable. Wait at least 90 seconds. Replace occupant classification ECU. See OCCUPANT CLASSIFICATION ELECTRONIC CONTROL UNIT (ECU)  under REMOVAL & INSTALLATION. Perform occupant classification ECU initialization. See OCCUPANT CLASSIFICATION ELECTRONIC CONTROL UNIT (ECU) INITIALIZATION PROCEDURE  under DIAGNOSTICS. Go to next step.
  9. Connect occupant classification ECU connectors, if necessary. 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 B1790 is retrieved, replace air bag sensor assembly. If DTC B1790 is not retrieved, test is complete.
  10. Turn ignition switch to LOCK position. Disconnect negative battery cable. Wait at least 90 seconds. Disconnect occupant classification system connector BE1, located under right front seat. Connect negative battery cable. Turn ignition switch to ON position. Measure voltage between ground and harness side of occupant classification system connector BE1, terminal No. 1 (Blue wire). See Figure. Measure voltage between ground and harness side of occupant classification system connector BE1, terminal No. 4 (Yellow wire). If voltage is less than one volt, repair or replace wiring harness between occupant classification system connector BE1 and air bag sensor assembly. If voltage is more than one volt, repair or replace wiring harness between occupant classification system connector BE1 and occupant classification ECU.
  11. Disconnect occupant classification system connector BE1, located under right front seat. Measure resistance between harness side of occupant classification system connector BE1, terminal No. 1 (Blue wire) and No. 4 (Yellow wire). See Figure. If resistance is less than one ohm, repair or replace wiring harness between occupant classification system connector BE1 and air bag sensor assembly. If resistance is more than one ohm, repair or replace wiring harness between occupant classification system connector BE1 and occupant classification ECU.
  12. Disconnect occupant classification system connector BE1, located under right front seat. Measure resistance between harness side of occupant classification system connector BE1, terminal No. 1 (Blue wire) and No. 4 (Yellow wire). See Figure. If resistance is more than one megohm, repair or replace wiring harness between occupant classification system connector BE1 and air bag sensor assembly. If resistance is less than one megohm, repair or replace wiring harness between occupant classification system connector BE1 and occupant classification ECU.
  13. Disconnect occupant classification system connector BE1, located under right front seat. Measure resistance between ground and harness side of occupant classification system connector BE1, terminal No. 1 (Blue wire). See Figure. Measure resistance between ground and harness side of occupant classification system connector BE1, terminal No. 4 (Yellow wire). If resistance is more than one megohm, repair or replace wiring harness between occupant classification system connector BE1 and air bag sensor assembly. If resistance is less than one megohm, repair or replace wiring harness between occupant classification system connector BE1 and occupant classification ECU.
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