1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Code 1, Code 2: O2 Sensor

NOTE: For wiring diagrams, see WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. For vacuum diagrams, see VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section.
  1. Turn ignition off. Remove ACG fuse in underdash fuse box for 10 seconds to reset ECU. Start and warm engine until cooling fan comes on.
  2. Place manual transmission in fourth gear (A/T in 2nd). Starting at 1200 RPM, accelerate at wide open throttle for at least 5 seconds, and then decelerate with throttle fully closed for at least 5 seconds. Accelerate and decelerate about 5 times.
  3. Connect jumper wire to diagnostic connector. Check if CHECK ENGINE light flashes Code 1 or 2. If light is not on, problem is intermittent. Check for poor connections at O2 sensor, ECU and connector C353 at right shock tower. If light flashes Code 1 and/or 2, perform test for Code 43 and/or 44.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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