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Home › Acura › 1990 › Legend Base, 4D Sedan, Automatic › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › Code 31: A/T FI Signal "B"

Code 31: A/T FI Signal "B"

  1. Turn ignition off. Remove alternator sense fuse in under-hood relay box for 10 seconds to reset ECU. Test drive vehicle for several miles so that transmission upshifts and downshifts several times. After test drive, observe CHECK ENGINE and Red LED lights. If lights are not on, failure is intermittent.
  2. Check for poor or loose connections at connectors C315 and C404. If CHECK ENGINE light is on, and Red LED indicates Code 31, turn ignition off. Connect ECU test harness to ECU. Disconnect 22-pin connector from automatic transmission control unit. Check for continuity between D4 and ground.
  3. If continuity is present, repair short in Blue/Red wire between ECU terminal D4 an automatic transmission control unit. If continuity is not present, check for continuity on Blue/Red wire between D4 and 22-pin connector of automatic transmission automatic transmission control unit.
  4. If continuity does not exist, repair open in Blue/Red wire between D4 and automatic transmission control unit. If continuity exists, substitute a known good ECU. If system operates properly, replace original ECU.
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