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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:
    • For DTC P1400, go to next step.
    • For DTC P1401, go to step  6.
  2. DTC P1400: Verify Differential Pressure Feedback EGR (DPFEGR) Voltage -  Turn ignition on, engine off. Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access DPFEGR PID. Turn ignition off. If DPFEGR PID voltage reading was less than 0.2 volt, sensor voltage is less than acceptable minimum. Go to next step. If DPFEGR PID voltage reading was 0.2 volt or more, problem is intermittent. Go to step  14.
  3. Induce Opposite DPFEGR Sensor Voltage -  Disconnect DPFEGR sensor 3-pin harness connector. See Fig 1. Turn ignition on, engine off. Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access DPFEGR PID. Turn ignition off. If DPFEGR PID value reading is not 4-6 volts, go to next step. If DPFEGR PID value reading is 4-6 volts, replace DPFEGR sensor. After repair, go to step  15.
    Fig 1: Identifying DPFEGR Sensor Circuits & 3-Pin Harness Connector Terminals
    G00158990Courtesy of MAZDA MOTORS CORP.
  4. Measure VREF Voltage At DPFEGR Sensor Vehicle Harness Connector -  Turn ignition on, engine off. Measure voltage between VREF and SIG RTN at DPFEGR sensor 3-pin harness connector. Turn ignition off. If VREF voltage reading is between 4-6 volts, go to next step. If VREF voltage reading is not 4-6 volts, VREF voltage is out of range. Refer to VEHICLE REFERENCE VOLTAGE  testing under SYSTEM TESTS.
  5. Check DPFE 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 terminal No. 65 (DPFEGR SIG) and terminal No. 91 (SIG RTN). Measure resistance between breakout box terminal No. 65 (DPFEGR SIG) and terminal No. 103 (PWR GND). If each resistance reading is more than 10,000 ohms, replace PCM. After repair, go to step  15. If each resistance reading is not more than 10,000 ohms, 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 -  Turn ignition on, engine off. Access DPFEGR PID with scan tool. Turn ignition off. If DPFEGR PID voltage reading was more than 4 volts, sensor voltage is more than acceptable maximum. Go to next step. If sensor voltage reading was 4 volts or less, problem is intermittent. Go to step  14.
  7. Check DPFEGR SIG For Short To PWR -  Disconnect DPFEGR sensor 3-pin harness connector. See Fig 1. Turn ignition on, engine off. Measure voltage between ground and DPFEGR SIG circuit at DPFEGR sensor 3-pin harness connector. Turn ignition off. If voltage reading was more than 10.5 volts, go to next step. If voltage reading was not as specified, go to step  9.
  8. Check DPFEGR SIG 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. Turn ignition on, engine off. Measure voltage between breakout box terminal No. 65 (DPFEGR SIG) and terminal No. 103 (PWR GND). Turn ignition off. If voltage reading is more than 10.5 volts, repair short circuit to power in Brown/Light Green wire between DPFEGR 3-pin harness connector and PCM 104-pin harness connector terminal No. 65. 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 PCM. After repair, go to step  15.
    9. NOTE: If scan tool communication concern exists during next step, remove fused jumper wire immediately and go to step  14.
  9. Induce Opposite DPFEGR Sensor Voltage -  Connect fused jumper wire between sensor DPFEGR SIG (Brown/Light Green wire) and SIG RTN (Orange wire) circuits 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 DPFEGR PID. Turn ignition OFF. If DPFEGR PID voltage reading was less than .05 volt, remove fused jumper wire and go to next step. If DPFEGR PID voltage reading was not as specified, go to step  12.
  10. Verify That VREF Is In Range -  Turn ignition on, engine off. Measure voltage between sensor VREF (Brown/White wire) and SIG RTN (Orange wire) circuits at DPFEGR sensor 3-pin harness connector. Turn ignition off. If VREF voltage reading was 4-6 volts, go to next step. If voltage reading was not as specified, VREF voltage reading is out-of-range. Refer to VEHICLE REFERENCE VOLTAGE  testing under SYSTEM TESTS.
  11. Check DPFEGR SIG For Short To VREF In Harness -  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 terminal No. 65 (DPFEGR SIG) and terminal No. 90 (VREF). If resistance reading is more than 10,000 ohms, replace DPFEGR sensor. After repair, go to step  15. If resistance reading is not as specified, repair short. 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 -  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. 65 (DPFEGR SIG) and DPFEGR sensor 3-pin harness connector (Brown/Light Green wire). If resistance reading is less than 5 ohms, go to next step. If resistance reading is not as specified, 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 between breakout box terminal No. 91 and DPFEGR sensor 3-pin harness connector (Orange wire). If resistance reading is less than 5 ohms, replace PCM. After repair, go to step  15. If resistance reading is not as specified, repair open circuit in Orange wire between DPFEGR sensor 3-pin harness connector and PCM 104-pin harness connector terminal No. 91. After repair, go to step  15.
  14. Wiggle Test DPFEGR Sensor & Harness -  Turn ignition on, engine off. Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access DPFEGR PID. Observe DPFEGR PID for an indication of fault while performing following:
    • 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. If a fault is indicated, isolate fault and repair as necessary. After repair, go to next step. If a fault is not indicated, problem is intermittent. 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 present, trouble shooting is complete.
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