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Home >> Lexus >> 1995 >> SC 400 >> Repair and Diagnosis >> Brakes >> Traction Control >> Traction Control System >> Circuit Tests >> DTC 45 Or 46 - Main Throttle Position Sensor Circuit >> Diagnosis & Repair

Diagnosis & Repair

  1. Determine if any engine DTCs are present. See appropriate TESTS W/CODES article in ENGINE PERFORMANCE section. Repair as needed. If no engine DTCs exist, go to next step.
  2. Access TRAC ECU. DO NOT  disconnect connectors. Remove air intake duct at throttle body. Turn ignition on. Backprobing TRAC ECU connector T13, measure voltage between ground and terminal No. 8. Monitor voltage while opening main throttle valve to wide open throttle. Voltage should be 1.5 volts or less with throttle fully closed, and 3-4.5 volts with throttle fully open. If voltage is within specification, go to step 7). If voltage is not within specification, go to next step.
  3. Turn ignition off. Check continuity of VTH circuit between TRAC ECU and ECM. Repair as needed. If circuit is okay, go to next step.
  4. Install ECM test harness. See Figure. Disconnect TRAC ECU harness connectors. Turn ignition on. Measure voltage between ground and terminal No. 40 on test connector "A". Monitor voltage while opening main throttle valve to wide open throttle. Voltage should be one volt or less with throttle fully closed, and 10-14 volts with throttle fully open. If voltage is within specification, replace TRAC ECU. If voltage is not within specification, go to next step.
  5. Measure voltage between terminals No. 43 and 65 on test connector "B". Monitor voltage while opening main throttle valve to wide open throttle. Voltage should be .3-.8 volts with throttle fully closed, and 3.2-4.9 volts with throttle fully open. If voltage is within specification, replace ECM. If voltage is not within specification, go to next step.
  6. Turn ignition off. Check continuity of VTA1 circuit between main TP sensor and ECM. Repair as needed. Ensure circuit is not shorted to ground. If circuit is okay, adjust or replace main TP sensor. See appropriate SYSTEM/COMPONENT TESTS article in ENGINE PERFORMANCE section.
  7. Turn ignition on. Backprobing TRAC ECU harness connector T13, measure voltage between ground and terminal No. 10. Monitor voltage while opening main throttle valve to wide open throttle. Voltage should be one volt or less with throttle fully closed, and 10-14 volts with throttle fully open. If voltage is within specification, replace TRAC ECU. If voltage is not within specification, go to next step.
  8. Turn ignition off. Disconnect TRAC ECU harness connector T13. Turn ignition on. Measure voltage between ground and terminal No. 10. Monitor voltage while opening main throttle valve to wide open throttle. Voltage should be one volt or less with throttle fully closed, and 10-14 volts with throttle fully open. If voltage is within specification, replace TRAC ECU. If voltage is not within specification, go to next step.
  9. Turn ignition off. Check continuity of IDL1 circuit between TRAC ECU and ECM. Repair as needed. Ensure circuit is not shorted to ground. If circuit is okay, go to next step.
  10. Inspect main TP sensor operation. See appropriate SYSTEM/COMPONENT TESTS article in ENGINE PERFORMANCE section. Adjust or replace as needed. If main TP sensor is okay, replace ECM.
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