Diagnostic Procedure

Verify Related Repair Information Availability - Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step 8.
Inspect For Other DTCs - Turn ignition off, then start engine. Using scan tool, check for other DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present, go to next step. If any other DTCs are present, go to appropriate trouble shooting procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
Inspect Vacuum Hose Condition - Check for vacuum hoses for clogging, damage, freezing or leaks. If no problems are present, go to next step. If any problems are present, diagnose and repair as necessary. After repair, go to step 8.
Inspect EGR Valve Malfunction - Check EGR valve operation. See EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If EGR valve is operating properly, go to next step. If EGR valve is not operating properly, replace EGR valve. After repair, go to step 8.
Inspect EGR Boost Sensor Malfunction - Check EGR boost sensor operation. See EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If EGR boost sensor is okay, go to next step. If EGR boost sensor is faulty, replace EGR boost sensor. After repair, go to step 8.
Inspect EGR Boost Sensor Solenoid Valve - Start engine. Using scan tool, check operation of EGR boost sensor solenoid valve. See EGR BOOST SENSOR SOLENOID VALVE under RELAYS & SOLENOIDS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If EGR boost sensor solenoid valve is okay, go to next step. If EGR boost sensor solenoid valve is faulty, replace EGR boost sensor solenoid valve. After repair, go to step 8.
Inspect EGR Valve Passage - Turn ignition off. Remove EGR valve. Check EGR passage and gasket installation. If passage is clear and gasket is installed properly, go to next step. If passage is blocked or gasket is not installed correctly, clean out passage or replace gasket and reinstall EGR valve. After repair, go to next step.
Monitor EGR System By Drive Mode - Reconnect all connectors. Turn ignition on, engine off. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. Start engine. Perform MODE 1 - PCM ADAPTIVE MEMORY PROCEDURE DRIVE MODE and MODE 2 - EGR SYSTEM REPAIR VERIFICATION DRIVE MODE under SELF-DIAGNOSTIC SYSTEM. Access ON BOARD SYSTEM READINESS TEST menu of GENERIC OBD II FUNCTION and check EGR System Monitor completion status. If EGR System Monitor is complete, go to next step. If EGR System Monitor is not complete, repeat this step.
Verify Trouble Shooting Of DTC P0401 Completed - Using scan tool, access DIAGNOSTIC MONITORING TEST RESULTS. If TEST ID 10:41:00 value is within specification, go to next step. If TEST ID 10:41:00 value is not within specification, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to next step.
Verify After Repair Procedure - Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, follow appropriate DTC diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .