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Diagnostic Procedures

  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed:
    • For DTC P1400, go to step  2 .
    • For DTC P1401, go to step  6 .
  2. DTC P1400: Verify Differential Pressure Feedback EGR (DPFEGR) Voltage -  With KOEO, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe DPFEGR PID. Turn ignition off. If DPFEGR PID voltage reading was less than 0.2 volt, DPFEGR sensor voltage is less than acceptable minimum. Go to next step. If DPFEGR PID voltage reading was 0.2 volt or more, fault is intermittent. Go to step  14 .
  3. Induce Opposite DPFEGR Sensor Voltage -  Disconnect DPFEGR sensor 3-pin harness connector. With KOEO, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe DPFEGR PID. Turn ignition off. If DPFEGR PID voltage reading is 4-6 volts, replace faulty DPFEGR sensor. After repair, go to step  15 . If DPFEGR PID voltage reading is not 4-6 volts, go to next step.
  4. Measure VREF Voltage At DPFEGR Sensor Vehicle Harness Connector -  With KOEO, measure voltage between VREF circuit (Brown/White wire) and SIG RTN circuit (Gray/Red wire) at DPFEGR sensor 3-pin harness connector. See Fig 1 . Turn ignition off. If VREF voltage reading is 4-6 volts, go to next step. If VREF voltage reading is not 4-6 volts, VREF voltage is out of range. See VEHICLE REFERENCE VOLTAGE  testing under SYSTEM TESTS.
    Fig 1: Identifying DPFEGR Sensor Harness Connector Circuits
    G00155552Courtesy of MAZDA MOTORS CORP.
  5. Check DPFEGR Circuit For Shorts To Ground & SIG RTN -  Disconnect scan tool from DLC. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance between breakout box terminals No. 65 (DPFEGR SIG circuit) and No. 91 (SIG RTN circuit). Record reading. Measure resistance between breakout box terminals No. 65 (DPFEGR SIG circuit) and No. 51 or 103 (SIG RTN circuit). Record reading. If each resistance reading is more than 10,000 ohms, replace faulty PCM. After repair, go to step  15 . If either 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 .
  6. DTC P1401: Verify DPFEGR PID Voltage -  With KOEO, using scan tool, access and observe DPFEGR PID. Turn ignition off. If DPFEGR PID voltage reading is more than 4 volts, DPFEGR sensor voltage is more than acceptable maximum. Go to next step. If DPFEGR PID voltage reading is 4 volts or less, fault is intermittent. Go to step  14 .
  7. Check DPFEGR SIG Circuit For Short To PWR -  Disconnect DPFEGR sensor 3-pin harness connector. With KOEO, measure voltage between DPFEGR SIG circuit (Brown/Light Green wire) between DPFEGR sensor 3-pin harness connector and negative battery terminal. Turn ignition off. If voltage reading is more than 10.5 volts, DPFEGR sensor voltage input is indicating a short to power. Go to next step. If voltage reading is 10.5 volts or less, go to step  9 .
  8. Check DPFEGR SIG Circuit For Short To PWR In Harness -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . With KOEO, measure voltage between breakout box terminals No. 65 (DPFEGR SIG circuit) and No. 103 (PWR GND circuit). Turn ignition off. If voltage reading is more than 10.5 volts, repair short circuit in Brown/Light Green wire between PCM 104-pin harness connector terminal No. 65 and DPFEGR valve 3-pin harness connector. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  15 . If voltage reading is 10.5 volts or less, replace faulty PCM. After repair, go to step  15 .
    9. NOTE: During next test step, if a scan tool communication concern is present, immediately remove fused jumper wire. Go to step  14 .
  9. Induce Opposite DPFEGR Sensor Voltage -  Connect a fused jumper wire between DPFEGR SIG circuit (Brown/Light Green wire) and SIG RTN circuit (Gray/Red wire) at DPFEGR sensor 3-pin harness connector. See Fig 1 . Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe DPFEGR PID. Turn ignition off. If DPFEGR PID voltage reading is less than 0.05 volt, remove fused jumper wire. Go to next step. If DPFEGR PID voltage reading is 0.05 volt or more, unable to induce opposite signal. Go to step  12 .
  10. Verify VREF Is In Range -  With KOEO, measure voltage between DPFEGR sensor 3-pin harness connector VREF circuit (Brown/White wire) and SIG RTN circuit (Gray/Red wire). Turn ignition off. If VREF voltage reading is 4-6 volts, go to next step. If VREF voltage reading is not 4-6 volts, go to VEHICLE REFERENCE VOLTAGE  testing under SYSTEM TESTS.
  11. Check DPFEGR SIG For Short To VREF In Harness -  Turn ignition off. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance between breakout box terminals No. 65 (DPFEGR SIG circuit) and No. 90 (VREF circuit). If resistance reading is more than 10,000 ohms, replace faulty DPFEGR sensor. After repair, go to step  15 . 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 .
  12. Check DPFEGR SIG Circuit For Open In Harness -  Turn ignition off. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance of DPFEGR SIG circuit (Brown/Light Green wire) between breakout box terminal No. 65 and DPFEGR sensor 3-pin harness connector. See Fig 1 . If resistance reading is less than 5 ohms, go to next step. If resistance reading is 5 ohms or more, repair open circuit in Brown/Light Green wire between PCM 104-pin harness connector terminal No. 65 and DPFEGR sensor 3-pin harness connector. After repair, go to step  15 .
  13. Check SIG RTN For Open In Harness -  Measure resistance of DPFEGR SIG RTN circuit (Brown/Light Green wire) between breakout box terminal No. 91 and DPFEGR sensor 3-pin harness connector. If resistance reading is less than 5 ohms, replace faulty PCM. After repair, go to step  15 . If resistance reading is 5 ohms or more, repair open circuit in Brown/Light Green wire between PCM 104-pin harness connector terminal No. 91 and DPFEGR sensor 3-pin harness connector. After repair, go to step  15 .
  14. Wiggle Test DPFEGR Sensor & Harness -  With KOEO, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe DPFEGR PID. Lightly tap on DPFEGR sensor, wiggle DPFEGR sensor 3-pin harness connector and vehicle harness between DPFEGR sensor and PCM. A fault is indicated by a sudden change in DPFEGR PID voltage reading. If a fault is indicated, isolate fault and repair as necessary. After repair, go to next step. If a fault is not indicated, unable to duplicate or identify fault at this time. See INTERMITTENT  testing under SYSTEM TESTS.
  15. Verify Trouble Shooting Of DTCs Completed -  Reconnect all electrical connectors. Clear DTC from PCM memory. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty 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 DTC is present, trouble shooting is complete.
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