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Home >> Acura >> 1991 >> Legend Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Code 12: EGR System
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Code 12: EGR System

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. Warm engine to normal operating temperature (cooling fan on). Drive vehicle for 10 minutes. Start engine, and connect jumper wire to diagnostic connector. Observe CHECK ENGINE light.
  2. If light does not flash, problem is intermittent. Check for poor connection of terminals of engine harness connector C355 at right shock tower, EGR valve, 4-pin connector at control box and ECU. Test drive, and check again.
  3. If CHECK ENGINE light flashes Code 12, disconnect vacuum hose No. 11 from EGR valve. Using a vacuum gauge, check for vacuum at vacuum hose. If no vacuum is found, go to step 6).
  4. If vacuum is found, disconnect 4-pin connector from control box. See Fig 1 . If vacuum is now present on vacuum hose No. 11, check hose routing. If hose routing is okay, replace EGR control solenoid.
    Fig 1: Identifying EGR Control Solenoid Connector
    G91B16288Courtesy of AMERICAN HONDA MOTOR CO., INC.
  5. If still no vacuum is present, check for continuity of White wire in 4-pin connector to ground. If continuity is present, repair short in White wire between EGR control solenoid and ECU terminal A11. If no continuity is present, try a known good ECU. If condition goes away, replace ECU.
  6. If no vacuum is present from step 3), connect vacuum pump to EGR valve, and apply 8 in. Hg. If EGR valve does not hold vacuum and/or engine does not stall, replace EGR valve. If EGR causes engine to stall, turn ignition off.
  7. Disconnect 4-pin connector at control box. Turn ignition on. Measure voltage between Black/Yellow (positive) wire terminal and ground. If battery voltage is not present, repair open in Black/Yellow wire between EGR control solenoid valve and fuse No. 22.
  8. If battery voltage is present, reconnect vacuum gauge to hose No. 11. Start engine, and allow it to idle. Connect wire terminal "A" to battery positive and "B" wire terminal to ground. See Fig 1 . If gauge does not read 8 in. Hg within one second, go to next step. If vacuum does change as described, go to step 10).
  9. Turn ignition off, and ensure vacuum hoses No. 5 and 11 are clear and routed correctly. Disconnect lower EGR control solenoid hose, and connect a vacuum gauge to hose. Start engine, and check for about 6-10 in. Hg. If vacuum is as described, replace EGR control solenoid. If vacuum is not 6-10 in. Hg, replace Constant Vacuum Control (CVC) valve.
  10. If gauge reads 8 in. Hg within one second, turn ignition off. Reconnect 4-pin connector at control box. Connect Test Harness (07LAJ-PT3020A ) to EGR lift sensor. See Fig 2 . Turn ignition on. Measure voltage between test harness Red (positive) and Green (negative) wires. If about 5 volts are present, go to step 12).
    Fig 2: Installing Test Harness to EGR Lift Sensor
    G91C16289Courtesy of AMERICAN HONDA MOTOR CO., INC.
  11. If about 5 volts are not present, repair open in Yellow/White wire between ECU terminal D20 and EGR lift sensor. If 5 volts are still not present, repair open in Green/White wire between ECU terminal D22 and EGR lift sensor. If wire is okay, substitute a known good ECU. If 5 volts are present, replace ECU.
  12. If about 5 volts are present from test in step 10), measure voltage between test harness White (positive) and Green (negative) wires. If about 1.2 volts are not present, replace EGR valve or repair short in Black/White wire between ECU terminal D12 and EGR lift sensor. If EGR valve and wire are okay, substitute a known good ECU. If proper voltage is available, replace ECU.
  13. If about 1.2 volts are present, apply and release vacuum to EGR valve. If voltage does not change from about 1.2 to 4.0 volts, replace EGR valve. If voltage changes as specified, reconnect No. 11 hose to EGR valve. Turn ignition off.
  14. Connect ECU test harness to ECU. See Figure . Start engine, and allow it to idle. Measure voltage between terminals D12 and D22. If about 1.2 volts are not present, repair open in Black/White wire between D12 and EGR lift sensor.
  15. If 1.2 volts are present, connect a jumper wire between ECU terminals A11 and A26. If engine does not stall, repair open in White wire between terminal A11 and EGR control solenoid. If engine stalls, substitute a known good ECU. If condition goes away, replace ECU.
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