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DTC P0401: EGR Flow Too Low: Testing

NOTE: Ensure freeze frame data has been recorded. Check for service bulletins and on-line information.
  1. Turn ignition off, then on. If no other DTCs are present, go to next step. If any other DTCs are present, repair other DTCs first.
  2. Check all vacuum hoses for clogging, damage or leaks. If no problems are found, go to next step. If any problems are present, repair as necessary. After repair, go to step  7 .
  3. Star engine. Warm engine to operating temperature. Using scan tool, select SEGRP PID. Operate EGR at 0 to 18 steps. If engine speed drops or engine stalls, go to next step. If RPM does not change, replace EGR valve. After repair, go to step  7 .
  4. Turn ignition off. Turn ignition on. Using scan tool, select BARO V PID. Disconnect EGR boost sensor vacuum hose. Using a vacuum pump, apply vacuum to EGR boost sensor. If BARO V PID decreases, go to next step. If BARO PID does not decrease, replace EGR boost sensor. After repair, go to step  7 .
  5. Start engine. Using scan tool, select EGRBV off simulation. If vacuum is not felt at vacuum hose during 3 second test, go to next step. If vacuum is felt at vacuum hose during 3 second test, replace EGR boost solenoid valve. After repair, go to step  7 .
  6. Turn ignition off. Remove EGR valve. If gasket is okay, go to next step. If gasket installation is faulty, repair as necessary. After repair, go to next step.
  7. Reconnect all components. Turn ignition on. Using scan tool, clear DTC. Start engine. Conduct Drive Mode No. 1 under DRIVE CYCLE PROCEDURE. See SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Check RFC FLAG PID. If FLAG is on, go to next step. If FLAG is not on, repeat Drive Mode No. 1.
  8. Conduct Drive Mode No. 2 under DRIVE CYCLE PROCEDURE. See SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Using scan tool on-board system readiness test function, check EGR system monitor completion status. If system has been monitored, go to next step. If system has not been monitored, repeat Drive Mode No. 2.
  9. Reconnect all components. Using scan tool diagnostic monitoring test results function, check TEST ID 10:41:00. If value is okay, go to next step. If value is not okay, replace PCM. PCM is mounted to passenger floor, behind glove box. Go to next step.
  10. Perform after repair procedure. See AFTER REPAIR PROCEDURE  . If no DTC is present, testing is complete. If any DTC is present, go to appropriate test for diagnosis and repair.
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