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HOMESERVICE MANUALSMAZDA1999626 ES, 2.5 D, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 59 (ENGINE CONTROLS [SELF-DIAGNOSTICS 2.3L])DIAGNOSTIC TESTSDTC P0401: EGR FLOW INSUFFICIENT DETECTEDDIAGNOSTIC PROCEDURE
1999 Mazda 626 ES, 2.5 D, Standard

Diagnostic Procedure

1999 Mazda 626 ES, 2.5 D, StandardSECTION Diagnostic Procedure
WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
  1. If FREEZE FRAME DATA has been recorded, go to next step. If FREEZE FRAME DATA has not been recorded, record FREEZE FRAME DATA. Go to next step.
  2. Verify Related Repair Information Availability -  Check for related Service Bulletins and/or on-line repair information availability. If any related repair information is available, perform repair or diagnosis according to available repair information. If vehicle is not repaired, go to next step. If related repair information is not available, go to next step.
  3. Inspect For Other DTCs -  Turn ignition off, then on (engine off). If other DTCs have not been stored, go to next step. If other DTCs have been stored, repair circuit malfunction for applicable DTCs. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  4. Inspect Vacuum Hose Condition -  Inspect vacuum hoses for clogs, any damages, frozen, or vacuum leakage. If any malfunction is present, repair as necessary. After repair, go to step  8.
  5. Inspect EGR Valve Malfunction -  Perform EGR valve inspection. Refer to EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If EGR valve is okay, go to next step. If EGR valve is faulty, replace EGR valve. After repair, go to step  8.
  6. Inspect MAP Sensor Malfunction -  Perform MAP sensor inspection. Refer to MANIFOLD ABSOLUTE PRESSURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If MAP sensor is okay, go to next step. If MAP sensor is faulty, replace MAP sensor. After repair, go to step  8.
  7. Inspect EGR Valve Passage -  Turn ignition off. Remove EGR valve. If gasket installation is correct, go to next step. If gasket installation is incorrect, install gasket correctly. After repair, go to next step.
  8. Monitor EGR System By Drive Mode 1 -  Clear DTC from PCM memory using WDS or equivalent. Perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  under DRIVE CYCLES. Stop vehicle and access ON BOARD READINESS TEST to inspect DRIVE MODE completion status. Verify FUEL_EVAL PID status. If FUEL_EVAL PID changed to YES, go to next step. If FUEL_EVAL PID did not change to YES, retry this step.
  9. Monitor EGR System By Drive Mode 2 -  Perform MODE 2 - EGR SYSTEM REPAIR VERIFICATION DRIVE MODE  under DRIVE CYCLES. Stop vehicle and access ON BOARD READINESS TEST to inspect DRIVE MODE completion status. Verify FUEL_EVAL PID status. If FUEL_EVAL PID changed to YES, go to next step. If FUEL_EVAL PID did not change to YES, retry this step.
  10. Verify Trouble Shooting Of DTC P0401 Completed -  Make sure to reconnect all disconnected connectors. Access DIAGNOSTIC MONITORING TEST RESULTS. Verify TEST #10:31:83 (EGR pressure variation) value. Is value within specification, go to next step. If value is not within specification, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. After repair, go to next step.
  11. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If any DTCs are present, go to appropriate DTC inspection. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
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When to See a Mechanic

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.