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Home >> Toyota >> 2000 >> MR2 >> Repair and Diagnosis >> 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. 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 on driver's side of firewall behind driver's seat, luggage compartment lids and partition board. See Figure. Turn ignition on. Using DVOM, backprobe ECM harness connector and measure voltage between ground and terminal No. 6 (Green wire) at ECM harness connector E3. See Figure. 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 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. If problem exists, repair wiring as necessary. If problem does not exist, replace ECM.
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