1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Code 3: Map 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 engine, and connect jumper wire to diagnostic connector. Observe CHECK ENGINE light. If no codes are stored, problem is intermittent. Check for poor or loose connection at MAP sensor connector. Test drive, and check again.
  2. If CHECK ENGINE light flashes Code 3, turn ignition off. Disconnect 3-pin connector at MAP sensor. Turn ignition on. Measure voltage between Yellow/White (positive) and Green/White (negative) wires. If reading is about 5 volts, go to step 5). If reading is not about 5 volts, measure between Yellow/White wire and ground.
  3. If reading is about 5 volts, repair open in Green/White wire between ECU terminal D21 and MAP sensor. If reading is not about 5 volts, turn ignition off. Connect ECU test harness to ECU "D" connector. See Figure . Turn ignition on. Measure voltage between terminals D19 and D21.
  4. If voltage is about 5 volts, repair open in Yellow/White wire between D19 and MAP sensor. If voltage is not about 5 volts, substitute a known good ECU, and recheck. If voltage is now correct, replace original ECU.
  5. If voltage is about 5 volts from step 2), measure voltage between Red (positive) and Green/White (negative) wires.
  6. If reading is not about 5 volts, replace MAP sensor or repair short in Red wire between ECU terminal D19 and MAP sensor. If voltage is about 5 volts, turn ignition off. Reconnect MAP sensor. Connect ECU test harness between ECU and ECU connectors.
  7. Turn ignition on. Measure voltage between terminal D17 (positive) and D21 (negative). If voltage is not about 3 volts, replace MAP sensor. If there are about 3 volts present, substitute a known good ECU. If condition goes away, replace original ECU.
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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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