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Home >> Toyota >> 2001 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P1520: Stoplight Switch Signal Circuit (A/T Only) >> Diagnosis & Repair
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Diagnosis & Repair

  1. Check stoplight operation. If stoplights operate properly, go to next step. If stoplights do not operate properly, repair as necessary and retest system. See EXTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT.
  2. Access ECM behind passenger-side kick panel. See Figure. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between ground and terminal No. 15 (Red/Blue wire) at ECM harness connector E8. See Figure. Voltage should be 7.5-14.0 volts with brake pedal depressed, and less than 1.5 volts with brake pedal released. If voltage is not as specified, go to next step. If voltage is as specified, problem is intermittent. Check component and ECM connections.
  3. Check for short in wiring between ECM and stoplight switch. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace ECM.
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