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Self-Diagnostic Light No. 1 On

NOTE: Before proceeding with trouble shooting, check spark plugs for mis-firing. Spark plug mis-fire can set self-diagnostic light No. 1.
  1. Start engine and warm-up to normal operating temperature. Raise engine speed to 4000 RPM and quickly release throttle. Stop engine. Connect system checker harness between ECU and connector.
  2. Connect positive voltmeter probe to terminal C16 (White wire) and negative probe to terminal A18 (Black/Red wire). Turn ignition on. Move throttle to wide open position and then close throttle while watching voltmeter. Voltage should raise to over .6 volt at wide open throttle (WOT) and then fall below .4 volt when throttle is closed.
  3. If voltage is within specifications, replace ECU and retest. If voltage is not within specifications, test O2 sensor. Replace O2 sensor if defective. If O2 sensor tests okay, repair open circuit in White wire between O2 sensor and ECU.
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