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Home › Mazda › 2003 › B4000 Base, Automatic › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P0402: EGR System Malfunction › Diagnostic Procedures

Diagnostic Procedures

  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed, go to next step.
    2. NOTE: If DTC P1405 is in Continuous Memory, repair that DTC first.
  2. Check For EGR Flow At Idle With EGR Vacuum Hose Disconnected -  Disconnect EGR vacuum hose. Plug EGR vacuum hose. Perform KOER Self-Test. If able to complete KOER Self-Test and DTC P0402 is set or unable to run KOER Self-Test due to engine stall or no start, turn ignition off. There is possible EGR flow at idle. Inspect pressure hoses for pinching and icing. If hoses are okay, remove and inspect EGR valve and EGR tube for contamination or other damage. Repair as necessary. After repair, go to step  15 . If able to complete KOER Self-Test and DTC P0402 is not set, reconnect vacuum hose to EGR valve. Go to next step.
  3. Check For EGR Flow At Idle With EGR Vacuum Hose Connected -  Connect EGR vacuum hose. Perform KOER Self-Test. Turn ignition off. If able to complete KOER Self-Test and DTC P0402 is set or unable to run KOER Self-Test due to engine stall or no start, there is possible EGR flow at idle. Go to next step. If able to complete KOER Self-Test and DTC P0402 is not set, fault is intermittent. Inspect pressure hoses for pinching or icing. Repair as necessary. After repair, go to step  11 .
    4. NOTE: A pinched or plugged EGR vacuum hose may trap vacuum between EGR vacuum regulator solenoid and EGR valve not allowing EGR valve to close.
  4. Check EGR System Vacuum Hoses For Integrity & Connection -  Verify each EGR vacuum regulator hose is properly connected. Verify EGR valve vacuum hose is not pinched or plugged. Verify hoses are properly routed. If hoses are okay, reconnect vacuum hoses. Go to next step. If hoses are not okay, repair vacuum hoses as necessary. After repair, go to step  14 .
  5. Check DPFEGR Sensor Output By Applying Vacuum With Hand Pump -  Disconnect pressure hoses at DPFEGR sensor. Connect a hand vacuum pump to downstream connection at sensor (intake manifold side of sensor, smaller diameter pickup tube). With KOEO, access and record DPFEGR PID. Voltage reading should be 0.2-1.3 volts. Apply 8-9 in. Hg (27-30 kPa) vacuum to DPFEGR sensor. Hold vacuum for a few seconds. Observe DPFEGR PID. Voltage reading should be more than 4 volts. While observing DPFEGR PID, quickly release vacuum. Voltage reading should be less than 1.5 volts in less than 3 seconds. If voltage readings are within specification, reconnect DPFEGR sensor. Go to next step. If voltage readings are not within specification, replace faulty DPFEGR sensor. After repair, go to step  15 .
  6. Check For EGR Flow At Idle With EGR Vacuum Regulator (EGRVR) Solenoid Connector Off -  Disconnect vacuum hose at EGR valve and connect hose to vacuum gauge. Start engine and idle. While monitoring vacuum gauge, disconnect EGR vacuum regulator solenoid 2-pin harness connector. The EGR valve requires a vacuum of 1.6 in. Hg (5.4 kPa) to begin opening. If vacuum remains more then 1.6 in. Hg after EGR vacuum regulator solenoid is electrically disconnected, this indicates a mechanical fault in EGR vacuum regulator solenoid. Turn ignition off. If vacuum remained more then 1.6 in. Hg (5.4 kPa) at idle even after EGRVR solenoid is electrically disconnected, a fault is present in EGRVR solenoid. Go to next step. If vacuum did not remain more then 1.6 in. Hg (5.4 kPa) at idle even after EGRVR solenoid is electrically disconnected, go to step  8 .
    7. NOTE: A plugged EGR vacuum regulator solenoid vent will not allow EGR vacuum to vent to atmosphere.
  7. Inspect EGR Vacuum Regulator Solenoid Vent For Plugging -  Disconnect EGRVR solenoid vacuum hoses. Remove EGRVR solenoid vent cap (if removable). Remove filter and inspect for blockage or icing in some cases. With EGR vacuum supply port plugged, using a hand vacuum pump, apply 10-15 in. Hg (34-51 kPa) of vacuum directly to EGRVR solenoid vacuum source port. If vacuum holds or is slow to release to atmosphere, EGRVR solenoid vent could be plugged or restricted. If EGRVR solenoid vent or vent filter is plugged, repair EGRVR solenoid as necessary. If unable to repair, replace solenoid. After repair, go to step  15 . If EGRVR solenoid vent or vent filter is not plugged, replace faulty EGRVR solenoid. After repair, go to step  15 .
  8. Measure Resistance Across EGR Vacuum Regulator (EGRVR) Solenoid -  Disconnect EGRVR solenoid harness connector. Measure resistance of EGRVR solenoid. If resistance reading is 26-40 ohms, go to next step. If resistance reading is not 26-40 ohms, replace faulty EGRVR solenoid. After repair, go to step  15 .
  9. Check EGRVR Circuit For Short To Ground In Harness -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance between breakout box terminal No. 47 and terminals No. 51 and 103. If resistance reading is more than 10,000 ohms, go to next step. If resistance reading is 10,000 ohms or less, repair short circuit. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  15 .
  10. Check EGRVR Circuit For Short To VREF -  Measure resistance between breakout box terminals No. 47 and 90. If resistance reading is more than 10,000 ohms, replace faulty PCM. After repair, go to step  15 . If resistance reading is 10,000 ohms or less, repair short circuit. After repair, go to step  15 .
  11. Check DPFEGR Sensor Output By Applying Vacuum With Hand Pump -  Disconnect DPFEGR sensor pressure hoses. Connect a hand vacuum pump to downstream connection at sensor (intake manifold side of sensor, smaller diameter pickup tube). With KOEO, access and record DPFEGR PID. Voltage reading should be 0.2-1.3 volts. Apply 8-9 in. Hg (27-30 kPa) vacuum to DPFEGR sensor. Hold vacuum for a few seconds. Observe DPFEGR PID. Voltage reading should be more than 4 volts. While observing DPFEGR PID, quickly release vacuum. Voltage reading should be less than 1.5 volts in less than 3 seconds. Turn ignition off. If voltage readings are within specification, reconnect DPFEGR sensor. Go to next step. If voltage readings are not within specification, replace faulty DPFEGR sensor. After repair, go to step  15 .
  12. Check DPFEGR Sensor Voltage While Exercising EGR Valve -  With KOEO, observe DPFEGR PID. Record reading. Typical DPFEGR sensor voltage with no EGR flow is 0.2-1.3 volts. Disconnect and plug vacuum hose at EGR valve. Connect a hand vacuum pump to EGR valve. Start engine and idle. Observe DPFEGR PID at idle and compare to KOEO voltage. A higher voltage at idle may be caused by a non-seating EGR valve. Apply just enough vacuum to EGR valve to open EGR valve without stalling engine 2-3 in. Hg (7-10 kPa). Release vacuum. Repeat applying and releasing vacuum several times while observing DPFEGR PID. DPFEGR PID should increase as valve begins to open and return to initial voltage as vacuum is released. A slow return to voltage could be an indication of a binding or slow-closing EGR valve. Turn ignition off. If DPFEGR PID indicates an open, binding or slow-closing EGR valve, inspect EGR valve for signs of contamination, unusual wear, carbon deposit, or binding. Repair or replace as necessary. After repair, go to step  15 . If DPFEGR PID does not indicate an open, binding or slow-closing EGR valve, go to next step.
    13. NOTE: An intermittent short to GND in EGR vacuum regulator circuit will cause the vacuum applied to EGR valve to be higher than normal while short is present. The vacuum available at EGR valve at idle is normally less than one in. Hg (3.4 kPa) and takes approximately 1.6 in. Hg (5.4 kPa) for valve to begin opening.
  13. Monitor EGR Valve Vacuum While Wiggling EGRVR Circuit -  Disconnect vacuum hose at EGR valve from hand vacuum pump and connect hose to a vacuum gauge. With KOER, observe vacuum gauge for an indication of a fault while lightly tapping on EGRVR solenoid, wiggling EGRVR solenoid connector and vehicle wiring harness between EGRVR solenoid and PCM. A fault is indicated by a sudden jump in vacuum reading. Turn ignition off. If no fault is indicated, reconnect vacuum hose. Go to next step. If a fault is indicated, isolate fault and repair as necessary. After repair, go to step  15 .
  14. Inspect EGRVR Solenoid & Vacuum Hoses For Potential Plugging -  Remove EGRVR solenoid vent filter and inspect for contamination and excessive water absorption. In cold climates excessive water in filter could freeze and plug EGRVR solenoid vent. Inspect EGR vacuum hose for possible blockage and pinching. Turn ignition off. If plugging or contamination was found, repair EGRVR solenoid or EGR vacuum hose as necessary. After repair, go to next step. If plugging or contamination was not found, fault is not present at this time. For further diagnostics, see INTERMITTENT  testing under SYSTEM TESTS.
  15. Verify Trouble Shooting Of DTCs Completed -  Reconnect all electrical connectors. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any DTC is present, replace PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTCs are set, trouble shooting is complete.
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