1991 Acura Legend Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Alternator Fr Signal

  1. Connect PGM-FI test harness between ECU and ECU connectors. Disconnect connector "D" from main wire harness only; DO NOT  disconnect from ECU. Turn ignition on. Check voltage between terminals D9 (positive) and A26 (negative). If voltage is NOT about 5 volts, substitute a good known ECU, and recheck.
  2. If voltage is about 5 volts, turn ignition off. Reconnect connector "D" to main harness. Start engine, and warm it to operating temperature. Check voltage between ECU terminals D9 (positive) and A26 (negative). If voltage does not decrease, go to step 4).
  3. If voltage decreases when headlights or rear defogger are turned on, alternator FR signal is okay. Turn ignition off. Remove alternator sensor fuse for 10 seconds to reset ECU.
  4. Disconnect connector "D" from ECU only. Disconnect negative battery cable from battery. Check for continuity between PGM-FI test harness terminal D9 and ground. If continuity is present, disconnect Green connector from alternator.
  5. Check again for continuity between PGM-FI test harness terminal D9 and ground. If continuity is not present, check alternator for possible failure. If continuity is present, repair Red/White wire between alternator and terminal D9 on ECU.
    NOTE: The following tests can only be performed with PGM-FI Test Harness (07LAJ-PT3010A ). Terminals on PGM-FI test harness connectors match terminals on ECU and ECU connectors. This allows the technician to test continuity of specified wires and resistance of devices when the ECU is disconnected. When ECU is connected to PGM-FI test harness, sensor input values can be monitored (at the test connector terminals) while engine is in operation. To identify ECU terminals, See Figure . ECU connectors are identified as "A", "B", "C" and "D" on harness.
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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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