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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> 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.
    NOTE: If DTC P1405 is in continuous memory, diagnose that first.

  2. Check For EGR Flow At Idle With EGR Vacuum Hose Disconnected

    Disconnect vacuum hose at EGR valve and plug hose. See Figure. Perform Key ON, Engine Running (KOER) Self-Test. If able to run KOER self-test, go to next step. If KOER DTC P0402 output or unable to run KOER self-test due to engine stall or no start, possible EGR flow at idle. Check pressure hoses first for pinching and icing. If okay, remove and inspect EGR valve and EGR tube for signs of contamination, unusual wear, carbon deposits, binding or damage. Repair as necessary. After repair, go to next step.

  3. Check For EGR Flow At Idle With EGR Vacuum Hose Connected

    Reconnect EGR vacuum hose. Perform KOER self-test. Turn ignition off. If able to run KOER self-test, fault is intermittent. Inspect pressure hoses for pinching or icing. Repair as necessary. After repair, go to step  11. If KOER DTC P0402 output or unable to run KOER self-test due to engine stall or no start, possible EGR flow at idle. Go to next step.
    NOTE: A pinched or plugged EGR vacuum hose can 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

    Trace each vacuum hose from EGR vacuum regulator solenoid and verify that each hose is connected properly. Refer to VACUUM DIAGRAMS article. Ensure EGR valve vacuum hose is not pinched or plugged and is routed properly. If vacuum hoses are okay, reconnect vacuum hoses and go to next step. If vacuum hoses are not okay, repair 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 or smaller diameter pickup tube). Turn ignition on, engine off. Access DPFEGR PID with scan tool and record PID value. Apply 8-9 in. Hg (27-30 kPa) vacuum to the DPFE sensor and hold for a few seconds. Quickly release vacuum. DPFEGR PID voltage reading must be 0.2-1.3 volts with ignition on and no vacuum applied. DPFEGR PID voltage reading must increase to more than 4.0 volts with vacuum applied. DPFEGR PID voltage reading must drop to less than 1.5 volts in less than 3 seconds when vacuum is released. If DPFEGR PID voltage reading did not indicate a fault in DPFEGR sensor, go to next step. If DPFEGR PID voltage reading indicated a fault in DPFEGR sensor, replace DPFEGR sensor. After repair, go to step  15.

  6. Check For EGR Flow At Idle With EGRVR Solenoid Connector Off

    Disconnect vacuum hose at EGR valve and connect hose to vacuum gauge. Start engine and bring to an idle. While monitoring vacuum gauge, disconnect EGRVR solenoid harness connector. EGR valve requires vacuum more than 1.6 in. Hg (5.4 kPa) to begin to open. If vacuum reading remains more than 1.6 in. Hg (5.4 kPa) after EGRVR solenoid harness connector is disconnected, this would indicate a mechanical fault in EGRVR solenoid. Turn ignition off. If EGR vacuum remained more than 1.6 in. Hg (5.4 kPa) at idle even after EGRVR solenoid harness connector was disconnected, go to next step. If EGR vacuum did not remain more than 1.6 in. Hg (5.4 kPa) at idle even after EGRVR solenoid harness connector was disconnected, go to step  8.
    NOTE: A plugged EGR vacuum regulator solenoid vent will not allow EGR vacuum to vent to atmosphere.

  7. Inspect EGRVR 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, apply 10-15 in. Hg (34-51 kPa) of vacuum directly to EGRVR solenoid vacuum source port with a hand vacuum pump. 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 not plugged or restricted, replace EGRVR solenoid. After repair, go to step  15. If EGRVR solenoid vent or vent filter is plugged or restricted, repair EGRVR solenoid as necessary. If unable to repair, replace EGRVR solenoid. After repair, go to step  15.

  8. Measure Resistance Across EGRVR Solenoid

    Disconnect EGRVR solenoid. Measure resistance across EGRVR solenoid terminals. If EGRVR solenoid resistance reading is 26-40 ohms, go to next step. If EGRVR solenoid resistance reading is not as specified, replace 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. 79 (2.0L) or terminal No. 47 (3.0L) (EGRVR) and breakout box terminals No. 51 and 103 (PWR GND). If resistance reading is more than 10,000 ohms, go to next step. If resistance reading is less than 10,000 ohms, repair short circuit. See WIRING DIAGRAMS article. After repair, go to step  15.

  10. Check EGRVR Circuit For Short To VREF

    Measure resistance between breakout box terminal No. 79 (2.0L) or terminal No. 47 (3.0L) (EGRVR) and terminal No. 90 (VREF). If resistance reading is more than 10,000 ohms, replace PCM. After repair, go to step  15. If resistance reading is less than 10,000 ohms, repair short circuit. See WIRING DIAGRAMS article. After repair, go to step  15.

  11. 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 or smaller diameter pickup tube). Turn ignition on, engine off. Access DPFEGR PID with scan tool and record PID value. Apply 8-9 in. Hg (27-30 kPa) vacuum to DPFEGR sensor and hold for a few seconds. Quickly release vacuum. DPFEGR PID voltage reading must be 0.2-1.3 volts with ignition on and no vacuum applied. DPFEGR PID voltage reading must increase to more than 4.0 volts with vacuum applied. DPFEGR PID voltage reading must drop to less than 1.5 volts in less than 3 seconds when vacuum is released. Turn ignition off. If DPFEGR PID voltage reading indicated a fault in the DPFEGR sensor, replace DPFEGR sensor. After repair, go to step  15. If DPFEGR PID voltage reading did not indicate a fault in the DPFEGR sensor, reconnect sensor and go to next step.

  12. Check DPFEGR Sensor Voltage While Exercising EGR Valve

    Turn ignition on, engine off. View DPFEGR PID with scan tool and record PID voltage 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 bring to idle. Observe DPFEGR PID voltage reading at idle and compare to KOEO voltage reading. A higher voltage at idle could be due to a non-seating EGR valve. Apply just enough vacuum to EGR valve to open it 2-3 in. Hg (7-10 kPa) without stalling engine and release vacuum. Repeat several times while observing DPFEGR PID on scan tool. DPFEGR PID voltage reading should increase as valve begins to open and return to initial voltage reading as vacuum is released. A slow to return voltage reading could be an indication of a binding or slow-closing EGR valve. Turn ignition off. If DPFEGR PID voltage reading did not indicate an open, binding or slow-closing EGR valve, go to next step. If DPFEGR PID voltage reading indicated an open, binding or slow-closing EGR valve, inspect EGR valve for signs of contamination, unusual wear, carbon deposits, binding or damage. Repair as necessary. After repair, go to step  15.
    NOTE: An intermittent short to GND in the EGR vacuum regulator circuit will cause the vacuum applied to the EGR valve to be higher than normal while short is present.

  13. Monitor EGR Valve Vacuum While Wiggling EGRVR Circuit

    Vacuum available at EGR valve at idle is normally below one in. Hg (3.4 kPa) and it takes about 1.6 in. Hg (5.4 kPa) for valve to begin to open. Disconnect vacuum hose at EGR valve from hand vacuum pump and connect hose to a vacuum gauge. Start engine. Observe vacuum gauge for an indication of a fault while performing the following:
    • Lightly tap on EGRVR solenoid.
    • Wiggle EGRVR solenoid connector and vehicle harness between solenoid and PCM.

    A fault is indicated by a sudden jump in vacuum reading. Turn ignition off. If a fault was indicated, isolate fault and repair as necessary. See WIRING DIAGRAMS article. After repair, go to step  15. If no fault was indicated, reconnect vacuum hose and go to next step.

  14. Inspect EGRVR Solenoid & Vacuum Hoses For Potential Plugging

    Remove EGRVR solenoid vent filter and inspect for contamination and excessive water absorption. In cold climate, excessive water in filter could freeze and plug EGRVR solenoid vent. Inspect EGR vacuum hose for possible blockage and pinching. If EGRVR solenoid vent or filter was contaminated or vacuum hose plugged, repair EGRVR solenoid or vacuum hose as necessary. After repair, go to next step. If EGRVR solenoid vent or filter were not contaminated or vacuum hose plugged, unable to duplicate or identify fault at this time. Refer to INTERMITTENT  testing under SYSTEM TESTS .

  15. Verify Trouble Shooting Of DTCs Completed

    Reconnect all disconnected connectors. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is not 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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