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Code 12 - EGR System

  1. Turn ignition off. Remove appropriate fuse for 10 seconds to reset ECU. See CLEARING CODES  . Start engine, and warm to normal operating temperature. Road test vehicle for about 10 minutes. Try to keep engine speed in 1700-2500 RPM range. Verify if CHECK ENGINE light is flashing Code 12. If Code 12 is present, go to next step. If Code 12 is not present, problem is intermittent. Check connectors at EGR valve and related circuits.
  2. With engine at idle, disconnect vacuum hose No. 16 from EGR valve. Using a hand-held vacuum pump/gauge, test for vacuum. If vacuum is present, go to next step. If vacuum is not present, go to step 5).
  3. Turn ignition off, and disconnect 4-wire connector from vacuum control box. Start engine, and again check for vacuum. If vacuum is present, check vacuum hose routing for entire EGR system. If hose routing is okay, replace EGR solenoid control valve.
  4. If vacuum is not present, check for short to ground in Pink wire between EGR solenoid control valve and ECU terminal A11. If wire is okay, substitute a known good ECU, and recheck. If condition is corrected, replace original ECU.
  5. Move vacuum pump to EGR valve, and apply 8 in. Hg to EGR valve. If vacuum does not hold and engine does not stall, replace faulty EGR valve or clean blocked EGR passages.
  6. If vacuum holds and engine stalls in step 5), disconnect 4-wire connector from control box. Measure voltage between Black/Yellow (+) terminal on main wire harness and ground. Battery voltage should be present. If battery voltage is not present, repair open in Black/Yellow wire between solenoid valve and fuse No. 2. If battery voltage is present, go to next step.
  7. Reconnect vacuum pump/gauge to EGR vacuum hose No. 16. Start engine, and let idle. Supply battery voltage to Black/Yellow wire terminal of box, and ground to Pink wire terminal of box. Reading at EGR valve hose should be about 8 in. Hg after one second. If reading is okay, go to step 10). If reading is not okay, go to step 8).
  8. Turn ignition off. Inspect hoses No. 16 and 24 for leaks, restrictions and misrouting. If problem is found, repair as necessary. If hoses are okay, disconnect lower hose on EGR control solenoid valve, and connect a vacuum gauge.
  9. Start engine, and allow to idle. If 6-10 in. Hg is not present, replace Constant Vacuum Control (CVC) Valve. If 6-10 in. Hg is present, replace EGR control solenoid valve.
  10. If gauge indicates 8 in. Hg in step 7), turn ignition off, and reconnect 4-pin connector. Connect Test Harness (07LAJ-PT3020A ) to EGR valve lift sensor harness. Turn ignition on. Measure voltage between Red (+) and Green (-) wire terminals. If about 5 volts is not present, repair open in Yellow/White wire between ECU terminal D20 and EGR valve or Green/White wire between ECU terminal D22 and EGR valve.
  11. If 5 volts is present, measure voltage between White (+) and Green (-) wire terminals. If approximately 1.2 volts are not present, replace EGR valve. Repair short in White/Black or Yellow wire between ECU terminal D12 and EGR valve lift sensor. If wire is okay, substitute a known good ECU. If proper voltage is present, replace original ECU.
  12. If 1.2 volts are present, observe voltmeter and slowly apply a continuous 8 in. Hg to valve. Repeat several times, fully releasing vacuum between checks. If maximum voltage is not 4 volts, replace EGR valve. If maximum voltage is 4 volts, ensure voltage consistently increases and decreases as vacuum increases and decreases.
  13. If voltage does not increase and decrease with vacuum, replace EGR valve. If voltage increases and decreases with vacuum, reconnect hose No. 16 to EGR valve. Turn ignition off. Connect ECU Test Harness to ECU. See Figure . Start engine, and allow to idle. Measure voltage between ECU positive terminal D12 and negative terminal D22. See Figure . If approximately 1.2 volts are not present, repair open in White/Black or Yellow wire between ECU terminal D12 and EGR valve lift sensor.
  14. If 1.2 volts are present, connect jumper between terminals A11 and A26. If engine does not stall, repair open in Pink wire between ECU terminal A11 and EGR control solenoid valve. If engine stalls, substitute a known good ECU. If condition goes away, replace original ECU.
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