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Home >> Toyota >> 2001 >> Sienna CE >> Repair and Diagnosis >> External Pages >> Different car >> Section 68 (Diagnosis - U150E) >> Diagnostic Tests >> DTC P1520: Stop Light Switch Circuit Malfunction >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. Warm the engine to normal operating temperature. Turn the ignition to the OFF position. Connect the scan tool to the DLC3 and turn the ignition switch to the ON position and turn ON the scan tool. Select the item STOP LIGHT SW in the DATALIST and monitor its value displayed on the scan tool. Depress the brake pedal. The reading should be ON. Release the pedal. The reading should now read OFF. If readings are as specified, replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE. If readings are not as specified, go to next step.
  2. Inspect stop light switch. See STOP LIGHT SWITCH  under COMPONENT TESTS. If stop light switch failed test, replace stoplight switch. If not, go to next step.
  3. Check circuit between stop light switch and ECM. If circuit is okay, replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE. If circuit is not okay, replace wiring harness and connector.
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