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Home >> Mazda >> 1986 >> 626 Base >> Repair and Diagnosis >> Engine Performance >> System >> EFI Control System >> Testing >> Diagnostic Procedure >> Code 5 (Feedback System)
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Code 5 (Feedback System)

  1. Start and run engine at 2500 RPM for one minute. See if tester still displays Code 5. If so, check whether or not Green light (on tester) comes on at idle.
  2. If Green light does not come on, check for air leaks in intake air system and for insufficient fuel injection. If Green light comes on, clean or replace spark plugs. After service, measure oxygen sensor voltage.
  3. If voltage is incorrect, replace oxygen sensor. If voltage is correct, measure voltage at terminal "2D" of ECU. If reading is correct, replace faulty ECU. If reading is incorrect, check for open or short circuit in wiring harness from oxygen sensor to terminal "2D" of ECU connector.
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