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Home >> Toyota >> 2001 >> 4Runner Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P1520: Stoplight Switch Signal Circuit >> Diagnosis & Repair
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Diagnosis & Repair

  1. If using Toyota hand-held tester, go to next step. If Toyota hand-held tester is not available, go to step  6.
  2. 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.
  3. Connect hand-held tester to Data Link Connector (DLC) No. 3. See Figure. Turn ignition on and then turn hand-held tester on.
  4. Monitor STP signal on hand-held tester while depressing and releasing brake pedal. STP signal should indicate ON with brake pedal depressed and OFF with brake pedal released. If STP signal is not as specified, go to next step. If STP signal is as specified, problem is intermittent. Check for defective connections or intermittent problem in wiring harness between stoplight switch and ECM, and for intermittent problem with stoplight switch. ECM is located behind glove box. See Figure. See WIRING DIAGRAMS article. Stoplight switch is located near top of brake pedal.
  5. Check wiring harness and electrical connectors between stoplight switch and ECM. See WIRING DIAGRAMS article. Stoplight switch is located near top of brake pedal. ECM is located behind glove box. See Figure. If wiring harness and electrical connectors are okay, replace ECM. If wiring harness or electrical connectors are defective, repair as necessary.
  6. 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.
  7. Remove glove box for access to ECM with electrical connectors still installed on ECM. See Figure. Turn ignition on.
  8. Using voltmeter, check voltage between body ground and terminal No. 20 (Green/White wire) at ECM electrical connector E14 while depressing and releasing brake pedal. See Figure. This is the STP terminal on ECM.
  9. With brake pedal depressed, voltage should be 7.5-14.0 volts. With brake pedal released, voltage should be less than 1.5 volts. If voltage is not within specification, go to next step. If voltage is within specification, problem is intermittent. Check for defective connections or intermittent problem in wiring harness and electrical connectors between stoplight switch and ECM, and for intermittent problem with stoplight switch. See WIRING DIAGRAMS article. Stoplight switch is located near top of brake pedal.
  10. Check wiring harness and electrical connectors between stoplight switch and ECM. See WIRING DIAGRAMS article. Stoplight switch is located near top of brake pedal. If wiring harness and electrical connectors are okay, replace ECM. If wiring harness or electrical connectors are defective, repair as necessary.
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