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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 69 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0401 Or DTC P1408 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed and Continuous Memory DTC P1406 appears, go to DTC P1405 OR P1406  troubleshooting. If KOER DTC 1408 does not appear with P0401, go to step  12. Otherwise, go to next step.
    2. NOTE: Since EGR vacuum hose is disconnected, ignore DTCs during this KOER self-test.
  2. Run KOER Self-Test While Monitoring EGR Vacuum -  Disconnect vacuum hose at EGR valve and connect hose to vacuum gauge. Start engine. Run Self-Test while monitoring vacuum gauge. About 30 seconds into test, EGR flow will be requested for a few seconds. Vacuum at this time should increase more than 1.6 in. Hg (5.4 kPa) to open valve. If vacuum increases to 3.0 in. Hg (10 kPa) or more at any time during KOER self-test, vacuum indicated is sufficient to open EGR valve. Fault is unlikely to be in EGR vacuum control system. Go to next step. If vacuum does not increase to specification, vacuum indicated is insufficient to open EGR valve. Go to step  6.
  3. Inspect DPFEGR Sensor Pressure Hoses -  Visually inspect both pressure hoses for reversed connection at DPFEGR sensor or at orifice tube assembly. Check both hoses for improper routing. Hoses should not be pinched or have dips where water could settle and freeze. Inspect both hoses for leaks and blockage. Inspect DPFEGR sensor and orifice tube assembly for blockage or damage at pick up tubes. If no fault is detected, go to next step. If there is a fault detected, repair vacuum hoses as necessary. After repair, go to step  6.
  4. 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 the smaller diameter pickup tube). Turn ignition on, engine off. Access DPFEGR PID with a 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 key on and no vacuum applied. DPFEGR PID voltage reading must increase to more than 4 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 next step. If DPFEGR PID voltage reading did not indicate a fault, go to step  6.
  5. Check EGR Valve Function By Applying Vacuum With Hand Pump -  Disconnect vacuum hose at EGR valve and plug hose. Connect hand vacuum pump to EGR valve. Start engine and bring to idle. Access DPFEGR and RPM PIDs with scan tool. Slowly apply 8-10 in. Hg (27-34 kPa) of vacuum to EGR valve and hold it for 10 seconds. If engine wants to stall, increase RPM with throttle to maintain a minimum of 1000 RPM. Look for following:
    • EGR valve starts opening at about 1.6 in. Hg (5.4 kPa) vacuum indicated by increasing DPFEGR PID voltage reading.
    • DPFEGR PID voltage reading increasing until EGR valve is fully open. DPFEGR PID should read 2.5 volts minimum with full vacuum applied.
    • DPFEGR PID voltage reading is steady when vacuum is held. If voltage drops within a few seconds, EGR valve or vacuum source could be leaking.
    If DPFEGR PID voltage reading indicated that EGR valve is operating properly in this test, restore vehicle to original condition. Go to step  11. If DPFEGR PID voltage reading did not indicate EGR valve is operating properly, remove and inspect EGR valve for signs of contamination, unusual wear, carbon deposits, binding, leaking diaphragm and other damage. If EGR valve is okay, look for an obstructed EGR port in intake manifold or plugged orifice tube assembly. Repair as necessary. After repair, go to step  17.
  6. Check Vacuum Source & Vacuum Hoses To & From EGR Vacuum Regulator (EGRVR) Solenoid -  Inspect vacuum lines between vacuum source and EGRVR solenoid and between EGRVR solenoid and EGR valve for leaks, kinks, disconnects, blockage, routing or any damage. Disconnect vacuum hoses at EGRVR solenoid. Connect EGRVR solenoid vacuum source hose to a vacuum gauge. With engine warm and at idle, take a vacuum reading. If vacuum gauge reading was a minimum of 15 in. Hg (51 kPa) at idle and vacuum lines are okay, restore vehicle to original condition. Go to next step. If vacuum gauge reading was not as specified or vacuum lines were faulty, isolate fault and repair as necessary. After repair, go to step  17.
  7. Check VPWR To EGRVR Solenoid -  Disconnect EGRVR solenoid. Turn ignition on, engine off. Measure voltage of VPWR circuit (White/Red wire) between ground and EGRVR solenoid harness connector. See Fig 1. If EGRVR solenoid VPWR voltage reading was more than 10.5 volts, go to next step. If EGRVR solenoid VPWR voltage reading was not as specified, repair open in EGRVR solenoid VPWR circuit (White/Red wire) between PCM 104-pin harness connector terminal No. 71 and EGRVR solenoid harness connector. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  17.
    Fig 1: Identifying EGR Vacuum Regulator (EGRVR) Solenoid Harness Connector Terminals
    G00158998Courtesy of MAZDA MOTORS CORP.
  8. Measure Resistance Across EGR Vacuum Regulator (EGRVR) Solenoid -  Measure resistance across EGRVR solenoid. 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  17.
  9. Check EGRVR Circuit For Short To PWR -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure. Turn ignition on, engine off. Measure EGRVR circuit voltage between ground and breakout box terminal No. 79 (2.0L) or terminal No. 47 (3.0L). Turn ignition off. If voltage reading was more than one volt, repair EGRVR circuit (Violet wire) for short to PWR between PCM 104-pin harness connector terminal No. 79 (2.0L) or terminal No. 47 (3.0L) and EGRVR solenoid harness connector. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  17. If voltage reading was not as specified, go to next step.
  10. Check EGRVR Circuit For Open In Harness -  Measure resistance of EGRVR circuit between breakout box terminal No. 79 (2.0L) or terminal No. 47 (3.0L) and EGRVR solenoid harness connector. See Fig 1. If resistance reading is less than 5 ohms, go to next step. If resistance reading is not as specified, repair open in EGRVR circuit (Violet wire) between PCM 104-pin harness connector terminal No. 79 (2.0L) or terminal No. 47 (3.0L) and EGRVR solenoid harness connector. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  17.
  11. Check EGRVR Solenoid Vacuum Output Capacity By Grounding EGRVR Circuit -  Remove breakout box. Reconnect PCM 104-pin harness connector and EGRVR solenoid harness connectors. Disconnect vacuum hose at EGR valve and connect to a vacuum gauge. Start engine. With engine at idle, connect fused jumper wire between ground and PCM 104-pin harness connector terminal No. 79 (2.0L) or terminal No. 47 (3.0L) (EGRVR). If vacuum gauge reading is 4 in. Hg (13.5 kPa) or more, replace PCM. After repair, go to step  17. If vacuum gauge reading was not as specified, replace EGRVR solenoid. After repair, go to step  17.
  12. Inspect EGR System For An Intermittent Failure -  Visually inspect EGR system for signs of intermittent failure. If no fault is found, go to next step. If a fault is found, repair fault as necessary. After repair, go to step  17.
  13. Inspect DPFEGR Sensor Pressure Hoses -  Visually inspect both pressure hoses for reversed connection at DPFEGR sensor or at orifice tube assembly. Inspect both hoses for improper routing. Hoses should not be pinched or have dips where water could settle and freeze. Inspect both hoses for leaks and blockage. Inspect DPFEGR sensor and orifice tube assembly for blockage or damage at pickup tubes. If no fault is detected, go to next step. If a fault is detected, repair pressure hoses as necessary. After repair, go to step  17.
  14. Check DPFEGR Sensor Output By Applying Vacuum With Hand Pump -  Disconnect pressure hoses at DPFEGR sensor. Connect hand vacuum pump to downstream connection at DPFEGR 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 turned on and no vacuum applied. The DPFEGR PID voltage reading must increase to more than 4 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 does not indicate a fault in DPFEGR sensor, go to next step. If DPFEGR PID voltage reading indicates a fault in DPFEGR sensor, replace DPFEGR sensor. After repair, go to step  17.
  15. Check EGR Valve Function By Applying Vacuum With Hand Pump -  Disconnect vacuum hose at EGR valve and plug hose. Connect a hand vacuum pump to EGR valve. Start engine and bring to idle. Access DPFEGR and RPM PIDs with scan tool. Slowly apply 5-10 in. Hg (17-34 kPa) of vacuum to EGR valve and hold it for 10 seconds. If engine wants to stall, increase RPM with throttle to maintain a minimum of 800 RPM. Look for following:
    • EGR valve starts opening at about 91.6 in. Hg (5.4 kPa) vacuum indicated by increasing DPFEGR PID voltage.
    • DPFEGR PID voltage increasing until EGR valve is fully open. DPFEGR PID should read 2.5 volts minimum with full vacuum applied.
    • DPFEGR PID voltage steady when vacuum is held. If voltage drops within a few seconds, EGR valve or vacuum source could be leaking.
    Turn ignition off. If DPFEGR PID voltage reading indicated that EGR valve is operating as described in this test, go to next step. If DPFEGR PID voltage reading indicated EGR valve was faulty, remove and inspect EGR valve for signs of contamination, unusual wear, carbon deposits, binding, leaking diaphragm and other damage. If EGR valve is okay, look for an obstructed EGR port in intake manifold. Repair as necessary. After repair, go to step  17.
  16. Inspect EGR Vacuum Signal Supply For Intermittent Failure -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector and PCM. See Figure. Disconnect plugged hose at EGR valve and connect to a vacuum gauge. Start engine. Connect fused jumper between ground and breakout box terminal No. 79 (2.0L) or terminal No. 47 (3.0L) (EGRVR) to activate EGR vacuum regulator solenoid to full ON. At idle, vacuum gauge should read above 4.0 in. Hg (13.5 kPa). Observe vacuum gauge for an indication of a fault while lightly tapping EGRVR solenoid and wiggling EGRVR solenoid connector, vacuum lines and vehicle harness between EGRVR solenoid and PCM. A fault is indicated by a sudden drop in vacuum reading. If a fault was indicated, isolate fault and repair as necessary. After repair, go to next step. If no fault was indicated, unable to duplicate or identify fault at this time. In cold climates, EGR valve may temporarily freeze shut and thaw when engine warms up causing intermittent DTC. Refer to INTERMITTENT  testing under SYSTEM TESTS .
  17. 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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