LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mazda >> 2000 >> B2500 SX, Standard >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Engine Controls Trouble Shooting (3 Of 5) >> Differential Pressure Feedback EGR (DPFEGR) Sensor Malfunction
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Differential Pressure Feedback EGR (DPFEGR) Sensor Malfunction

DTC P1400, P1401 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P1400, P1401 DPFEGR SENSOR MALFUNCTION
DETECTION CONDITION 
NOTE:
  • P1400 indicates the average voltage of the DPFEGR SIG circuit input is below the minimum (0.2 V).
  • P1401 indicates the average voltage of the DPFEGR SIG circuit input is above the maximum (4.5 V).
POSSIBLE CAUSE 
  • DPFEGR SIG shorted to GND (P1400).
  • DPFEGR SIG open (P1401).
  • DPFEGR SIG shorted to PWR (P1401).
  • VREF shorted to PWR (P1401).
  • VREF shorted to GND (P1400).
  • SIG RTN open (P1401).
  • Damaged DPFEGR sensor (P1400, P1401).
  • Damaged PCM (P1400, P1401).
HINT  DPFEGR Sensor Description 
  • Measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 to 5 V) to the PCM.
G03988154Courtesy of MAZDA MOTORS CORP.
G03988155Courtesy of MAZDA MOTORS CORP.
DTC P1400, P1401 INSPECTION

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed?
 Yes For DTC P1400: Go to next step. For DTC P1401: Go to step 6.
No Perform PCM Quick Test.
2 DTC P1400: VERIFY DIFFERENTIAL PRESSURE FEEDBACK EGR (DPFEGR) VOLTAGE
  • Key ON, Engine OFF (KOEO).
  • Access DPFEGR PID with NGS Tester.
  • Key OFF.
  • Was DPFEGR PID voltage less than 0.2 V? 
 Yes The DPFEGR sensor voltage is less than the acceptable minimum. Go to next step.
No Fault is intermittent. Go to step 14.
3 INDUCE OPPOSITE DPFEGR SENSOR VOLTAGE
  • Disconnect DPFEGR sensor connector.
  • Key ON, Engine OFF (KOEO).
  • Access DPFEGR PID with a NGS Tester.
  • Key OFF.
  • Is DPFEGR PID value between 4.0 and 6.0 V? 
 Yes Replace DPFEGR sensor. See ELECTRICAL COMPONENT LOCATOR .
Go to step 15.
No Go to next step.
4 MEASURE VREF VOLTAGE AT DPFEGR SENSOR VEHICLE HARNESS CONNECTOR
  • Key ON, Engine OFF (KOEO).
  • Measure voltage between VREF and SIG RTN at the DPFEGR sensor harness connector.
  • Key OFF.
  • Was VREF voltage between 4.0 and 6.0 V? 
 Yes Go to next step.
No VREF voltage is out of range.
See TEST 1: VEHICLE REFERENCE VOLTAGE (VREF) .
5 CHECK DPFEGR SIG CIRCUIT FOR SHORTS TO GROUND AND SIG RTN
  • Disconnect NGS Tester from DLC.
  • Disconnect PCM
  • Install Breakout Box, leave PCM disconnected.
  • Measure resistance between PCM test pin 65 (DPFEGR SIG) and PCM test pin 91 (SIG RTN)
  • Measure resistance between PCM test pin 65 (DPFEGR SIG) and PCM test pins 51 or 103 (PWR GND).
  • Is each resistance greater than 10K ohms? 
 Yes Replace PCM.
See COMPUTERIZED ENGINE CONTROLS .
Go to step 15.
No Repair short circuit. Go to step 15.
6 DTC P1401: VERIFY DPFEGR PID VOLTAGE
  • Key ON, Engine OFF (KOEO).
  • Access DPFEGR PID with NGS Tester.
  • Key OFF.
  • Was DPFEGR PID voltage greater than 4.0 V? 
 Yes The DPFEGR sensor voltage is greater than the acceptable maximum. Go to next step.
No The fault is intermittent. Go to step 14.
7 CHECK DPFEGR SIG FOR SHORT TO PWR
  • Disconnect DPFEGR sensor harness connector.
  • Key ON, Engine OFF (KOEO).
  • Measure voltage between DPFEGR SIG circuit at the DPFEGR sensor harness connector and battery ground.
  • Key OFF.
  • Was voltage greater than 10.5 V? 
 Yes The DPFEGR sensor voltage input is indicating a short to PWR. Go to next step.
No Go to step 9.
8 CHECK DPFEGR SIG FOR SHORT TO PWR IN HARNESS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Key ON, Engine OFF (KOEO).
  • Measure voltage between PCM test pin 65 (DPFEGR SIG) and PCM test pin 103 (PWR GND).
  • Key OFF.
  • Was voltage greater than 10.5 V? 
 Yes Repair short circuit. Go to step 15.
No Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 15.
9 INDUCE OPPOSITE DPFEGR SENSOR VOLTAGE
  • Connect a jumper wire between the sensor DPFEGR SIG and SIG RTN circuits at the DPFEGR sensor harness connection.
    NOTE: If a NGS Tester communication concern exists, remove jumper immediately and go to step 14.
  • Access DPFEGR PID with NGS Tester.
  • Key OFF.
  • Was DPFEGR PID voltage less than 0.05 V? 
 Yes Remove jumper. Go to next step.
No Unable to induce opposite signal. Go to step 12.
10 VERIFY THAT VREF IS IN RANGE
  • Key ON, Engine OFF (KOEO).
  • Measure voltage between the sensor VREF and SIG RTN at DPFEGR sensor harness connector.
  • Key OFF.
  • Was VREF voltage between 4.0 and 6.0 V? 
 Yes Go to next step.
No VREF is out of range
See TEST 1: VEHICLE REFERENCE VOLTAGE (VREF) .
11 CHECK DPFEGR SIG FOR SHORT TO VREF IN HARNESS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Measure the resistance between PCM test pin 65 (DPFEGR SIG) and PCM test pin 90 (VREF).
  • Is resistance greater than 10K ohms? 
 Yes Replace DPFEGR sensor. See ELECTRICAL COMPONENT LOCATOR .
Go to step 15.
No Repair short circuit. Go to step 15.
12 CHECK DPFEGR SIG CIRCUIT FOR OPEN IN HARNESS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Measure resistance of DPFEGR SIG circuit between PCM test pin 65 and DPFEGR sensor harness connector.
  • Is resistance less than 5.0 ohms? 
 Yes Go to next step.
No Repair open circuit. Go to step 15.
13 CHECK SIG RTN FOR OPEN IN HARNESS
  • Measure resistance of DPFEGR SIG RTN circuit between PCM test pin 91 and DPFEGR sensor harness connector.
  • Is resistance less than 5.0 ohms? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 15.
No Repair open circuit. Go to step 15.
14 WIGGLE TEST DPFEGR SENSOR AND HARNESS
  • Key ON, Engine OFF (KOEO).
  • Access DPFEGR PID with NGS Tester.
  • Observe DPFEGR PID for an indication of fault while performing the following:
    • Lightly tap on DPFEGR sensor; wiggle the DPFEGR sensor connector and vehicle harness between sensor and PCM. A fault is indicated by a sudden change in DPFEGR PID voltage.
  • Is a fault indicated? 
 Yes Isolate fault and repair as necessary. Go to step 15.
No Unable to duplicate or identify fault at this time.
See TEST 4: INTERMITTENT with DPFEGR PID data and list of possible causes.
15 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using NGS tester generic OBD-II function.
  • Perform PCM Quick Test.
  • Is same DTC present? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Repeat PCM QUICK TEST .
No If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.


DTC P1405, P1406 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P1405, P1406 DPFEGR SENSOR MALFUNCTION
DETECTION CONDITION 
  • P1405 indicates the exhaust manifold side (upstream) DPFEGR sensor pressure hose is off or plugged.
  • P1406 indicates the intake manifold side (downstream) DPFEGR sensor pressure hose is off or plugged.
POSSIBLE CAUSE 
  • Upstream or downstream pressure hose disconnected or improperly connected.
  • Upstream or downstream pressure hose plugged (by ice).
  • Plugged or damaged pressure pickup tubes.
  • Damaged DPFEGR sensor.
HINT  DPFEGR Sensor Description 
  • Measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 to 5 V) to the PCM.
G03988156Courtesy of MAZDA MOTORS CORP.
DTC P1405, P1406 INSPECTION

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed? 
 Yes Go to next step.
No Perform PCM Quick Test.
2 INSPECT PRESSURE HOSE CONNECTIONS
NOTE: If DTC P1406 is currently present, DTC P1408 will also appear in Key ON, Engine Running (KOER) Self Test
  • Inspect upstream or downstream hose at DPFEGR sensor and orifice tube assembly for disconnect or poor connection.
  • Is hose off or poorly connected? 
 Yes Reconnect hose(s) or repair as necessary. Go to step 6.
No Go to next step.
3 INSPECT PRESSURE HOSE FOR PLUGGING
NOTE: It is essential that the DPFEGR pressure hose is the correct service part and not a substitute.
  • Visually inspect upstream or downstream hose routing. Hose should not be pinched or have dips in it where water could settle and freeze.
  • Remove upstream or downstream hose and carefully inspect for plugging, water or leaks.
  • Is there a fault detected in the hose? 
 Yes Repair or replace hose(s) as necessary. Go to step 6.
No Go to next step.
4 CHECK ORIFICE TUBE ASSEMBLY AND DPFEGR SENSOR
  • Inspect connections at the DPFEGR sensor for plugging or damage at sensor.
  • Inspect the exhaust and intake manifold side pressure pickup tube and orifice tube assembly for plugging, loose connection or damage.
  • Is DPFEGR sensor or orifice tube assembly plugged, loose or damaged? 
 Yes Repair or replace DPFEGR sensor or orifice tube assembly as necessary. See ELECTRICAL COMPONENT LOCATOR .
Go to step 6.
No Go to next step.
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 the smaller diameter pickup tube).
  • Key ON, Engine OFF (KOEO).
  • Access DPFEGR PID with NGS Tester and note PID value. Apply 27-30 kPa (8-9 in-Hg) vacuum to the DPFEGR sensor and hold for a few seconds.
  • Quickly release vacuum.
    • The DPFEGR PID voltage must be between 0.2 and 1.3 volt with the key on and no vacuum applied.
    • The DPFEGR PID voltage must increase to greater than 4.0 volts with vacuum applied.
    • The DPFEGR PID voltage should drop to less than 1.5 volts in less than 3 seconds when vacuum is released.
    • Key OFF.
  • Does DPFEGR PID voltage indicate a fault in the DPFEGR sensor? 
 Yes Replace DPFEGR sensor. See ELECTRICAL COMPONENT LOCATOR .
Go to step 6.
No Fault not found.
See TEST 4: INTERMITTENT .
6 DRIVE CYCLE
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using NGS tester generic OBD-II function.
  • Perform EGR Monitor Drive Cycle,

    See DRIVE CYCLES .

  • Retrieve pending code.
  • Is same DTC present? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to next step.
No Go to next step.
7 VERIFY REPAIR
  • Perform PCM Quick Test.
  • Is any DTC present? 
 Yes Go to applicable DTC inspection.
No Troubleshooting complete.
scientia non olet · About LEMON Manuals