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Diagnostic Aids

Perform this test when instructed by QUICK TEST or other test. This test is only intended to diagnose the following:

NOTE: See TEST DIRECTORY  table for proper starting diagnostic step.
CIRCUIT PIN IDENTIFICATION

Circuit PCM Pin No. Wire Color
EGR 83 Gray
EGRT 76 (1)White/Purple
SIG RTN 58 Black/Yellow
(1) White/Red wire at EGR temperature sensor connector.
TEST DIRECTORY

DTC Action
P0400 Go To Step  1)
P0402 Go To Step  35)
P1400 Go To Step  20)
P1401 Go To Step  30)
P1402 Go To Step  35)

  1. 1) Inspect EGR System

    DTC P0400 indicates EGR flow malfunction. Possible causes are as follows:
    • Open or shorted EGR circuit.
    • EGR valve malfunction.
    • EGR Backpressure (EGR BPT) malfunction.
    • EGR passage obstructed or leaking.
    • EGR/EVAP control solenoid malfunction.
    • EGR temperature sensor malfunction.

    Check all vacuum hoses for damage or misrouting. See Fig 1. Check EGR/EVAP control solenoid and EGR temperature sensor wiring for corrosion or damage. See CIRCUIT PIN IDENTIFICATION  table. Repair as necessary. If vacuum hoses and wiring are okay, go to next step.

  2. 2) Check Vacuum To EGR Valve

    Start and run engine until it reaches normal operating temperature. Disconnect vacuum hose at EGR valve. Check vacuum at disconnected hose while driving at a steady cruising speed of 20-45 MPH. If vacuum is present, go to step  7). If vacuum is not present, go to next step.
    Fig 1: EGR System Schematic
    G99F02346Courtesy of FORD MOTOR CO.

  3. 3) Check Vacuum To EGR Modulator Valve

    Start and run engine to operating temperature. Disconnect vacuum hose between EGR modulator valve and EGR vacuum regulator solenoid valve from EGR modulator valve. Connect vacuum gauge to disconnected hose. Check vacuum at disconnected hose while driving at a steady cruising speed of 20-45 MPH. If vacuum is present at EGR modulator valve when vehicle is driven, go to next step. If vacuum is not present, go to step  10).

  4. 4) Check Modulator Valve Vent

    Disconnect vacuum hoses from EGR modulator valve. Connect vacuum pump to port "B". If vacuum holds, replace EGR modulator valve. If vacuum does not hold, go to next step.

  5. 5) Check EGR Modulator Valve Operation

    Disconnect EGR modulator vacuum lines. Connect vacuum gauge to port "C". Connect vacuum pump to port "B". Blow air into port "A" while applying vacuum to port "B". See Fig 2. If vacuum gauge indicates vacuum is present, go to next step. If vacuum gauge indicates vacuum is not present, replace EGR modulator valve.
    Fig 2: Identifying EGR Modulator Valve
    G99A02344Courtesy of FORD MOTOR CO.

  6. 6) Check For Exhaust System Leaks

    Start engine. Check exhaust system for leaks or cracks. Repair as necessary. If exhaust system is okay, replace plugged vacuum lines at EGR modulator valve.

  7. 7) Check EGR Valve

    Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR vacuum port. Apply vacuum to EGR valve while feeling for movement of EGR valve diaphragm. If diaphragm does not move, replace EGR valve and repeat QUICK TEST . If EGR valve diaphragm moves without sticking when vacuum is applied, go to step  30).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 10). No test procedures have been omitted.

  8. 10) Check Power To EGR Vacuum Regulator Solenoid Valve

    Turn ignition off. Disconnect EGR vacuum regulator solenoid valve connector. Turn ignition on. Measure voltage between VPWR circuit (Blue/Yellow wire) at EGR vacuum regulator solenoid valve harness connector and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open VPWR circuit (Blue/Yellow wire). Restore all electrical connections and repeat QUICK TEST .

  9. 11) Check EGR Vacuum Regulator Solenoid Valve

    Check vacuum hoses for damage or poor connection. Disconnect EGR vacuum regulator solenoid valve. Connect jumper wire between EGR vacuum regulator solenoid valve VPWR terminal (Blue/Yellow wire) and battery voltage. Connect additional jumper wire between EGR vacuum regulator solenoid valve EGR terminal (Gray wire) and ground. See Fig 3. Check if airflow is to specification. See EGR VACUUM REGULATOR SOLENOID VALVE PERFORMANCE  table. If EGR solenoid functions properly, go to next step. If EGR solenoid does not function properly, replace EGR solenoid.
    Fig 3: Identifying EGR Vacuum Regulator Solenoid Valve
    G99D02345Courtesy of FORD MOTOR CO.
    EGR VACUUM REGULATOR SOLENOID VALVE PERFORMANCE

    Power & Ground Applied Airflow Between Ports A & B Airflow Between Ports A & C
    Yes Yes No
    No No Yes

  10. 12) Check EGR Circuit

    Turn ignition off. Disconnect PCM harness connector. Disconnect EGR vacuum regulator solenoid valve connector. Measure resistance of EGR circuit between EGR vacuum regulator solenoid connector and PCM harness connector terminal No. 83 (Gray wire). Resistance should be less than 5 ohms. Measure resistance between ground and EGR vacuum regulator solenoid valve harness connector (Gray wire). Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, replace PCM. Restore all electrical connections and repeat QUICK TEST . If either resistance measurement is not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST .
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.

  11. 20) Check Power To EGR Vacuum Regulator Solenoid Valve

    Turn ignition off. Disconnect EGR vacuum regulator solenoid valve connector. Turn ignition on. Measure voltage of Blue/Yellow wire at EGR vacuum regulator solenoid harness connector. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open VPWR (Blue/Yellow) wire. Restore all electrical connections and repeat QUICK TEST .

  12. 21) Check EGR Vacuum Regulator Solenoid Valve

    Check vacuum hoses for damage or poor connection. Disconnect EGR vacuum regulator solenoid valve. Connect jumper wire between EGR vacuum regulator solenoid valve VPWR terminal (Blue/Yellow wire) and battery voltage. Connect additional jumper wire between EGR vacuum regulator solenoid valve EGR terminal (Gray wire) and ground. Check if airflow is to specification. See EGR VACUUM REGULATOR SOLENOID VALVE PERFORMANCE  table. If EGR solenoid functions properly, go to next step. If EGR solenoid does not function properly, replace EGR solenoid.

  13. 22) Check EGR Circuits

    Turn ignition off. Disconnect PCM harness connector, check for damaged or pushed out pins. Repair as necessary. Disconnect EGR vacuum regulator solenoid valve connector. Measure resistance of Gray wire between EGR purge control solenoid harness connector and PCM connector terminal No. 83. Resistance should be less than 5 ohms. Measure resistance between EGR vacuum regulator connector terminal (Gray wire) and ground. Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, go to next step. If resistance measurements are not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST .

  14. 23) Check EGR Circuit For Short To Power

    Ensure PCM is connected. Disconnect EGR vacuum regulator solenoid valve connector. Turn ignition on. Measure voltage of EGR circuit between EGR vacuum regulator solenoid valve harness connector (Gray wire) and ground. If voltage is less than one volt, replace PCM. If voltage is one volt or more, repair EGR circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 23) to step 30). No test procedures have been omitted.

  15. 30) Check EGR Temperature Sensor Resistance

    Disconnect EGR temperature (EGRT) sensor connector. Start and run engine until EGRT sensor reaches operating temperature. Turn ignition off. Measure resistance between EGRT (White/Purple) and SIG RTN (Black/Yellow) terminals of EGR temperature sensor at different temperatures. Compare resistance to EGR TEMPERATURE SENSOR RESISTANCE  table. If sensor is within specified resistance, go to next step. If sensor resistance is not within specification, replace EGR temperature sensor. Repeat QUICK TEST .
    EGR TEMPERATURE SENSOR RESISTANCE

    Coolant Temperature °F (°C) Sensor Resistance (M/ohms)
    68-120 (20-49) 2.25-2.55
    130-148 (55-65) 1.75-2.25
    150-165 (66-74) 1.40-1.75
    168-190 (76-88) 1.00-1.40

  16. 31) Check EGR Temperature Sensor

    Install NGS scan tool to OBD-II data link connector. Access EGRT PID. Disconnect vacuum line to EGR valve. Apply vacuum to EGR valve. Observe EGRT PID voltage as vacuum is applied. If voltage is 1.0-4.5 volts, EGR temperature sensor and circuit are okay. Fault may be intermittent, go to TEST Z  for intermittent diagnostic procedure. If voltage is not as specified, go to next step.

  17. 32) Check EGRT Circuit

    Turn ignition off. Disconnect PCM harness connector. Check for damaged or pushed out pins. Repair as necessary. Disconnect EGRT sensor connector. Measure resistance of EGRT circuit (White/Purple wire) between EGRT sensor connector and PCM connector terminal No. 83. Resistance should be less than 5 ohms. Reconnect connector. Measure resistance of EGRT circuit between PCM connector terminal No. 83 and ground. Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, go to next step. If either resistance measurement is not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST .

  18. 33) Check SIG RTN Wire

    Turn ignition off. Disconnect EGR temperature sensor harness connector. Disconnect PCM connector. Measure resistance of the Black/Yellow wire between EGR temperature sensor harness connector and PCM connector terminal No. 58. If resistance is less than 5 ohms, replace PCM. Restore all electrical connections and repeat QUICK TEST . If resistance is greater than 5 ohms, repair open Black/Yellow wire. Restore all electrical connections and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 33) to step 35). No test procedures have been omitted.
    19. NOTE: DTC P0402 indicates excessive EGR flow. Repair any other EGR related DTCs first.

  19. 35) Check EGR Valve Vacuum Lines
    Possible causes of DTC P0402 are:
    • EGR valve stuck open.
    • Faulty backpressure transducer.
    • Faulty EGR temperature sensor.
    • Faulty EGR/EVAP solenoid.
    • Misrouted vacuum lines.

    Turn ignition off. Check all vacuum lines for proper routing. Correct any vacuum line routing or leakage problems. If vacuum lines are okay, go to next step.

  20. 36) Check EGR Valve

    Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR vacuum port. Apply vacuum to EGR valve while feeling for movement of EGR valve diaphragm. If diaphragm does not move, replace EGR valve and repeat QUICK TEST . If EGR valve diaphragm moves without sticking when vacuum is applied, and closes fully when vacuum is released, go to next step.

  21. 37) Check EGR Vacuum Regulator Solenoid Valve

    Check vacuum hoses for damage or poor connection. Disconnect EGR vacuum regulator solenoid valve. Connect jumper wire between EGR vacuum regulator solenoid valve VPWR terminal (Blue/Yellow wire) and battery voltage. Connect additional jumper wire between EGR vacuum regulator solenoid valve EGR terminal (Gray wire) and ground. Check if airflow is to specification. See EGR VACUUM REGULATOR SOLENOID VALVE PERFORMANCE  table. If EGR solenoid functions properly, go to next step. If EGR solenoid does not function properly, replace EGR solenoid.

  22. 38) Check EGRT Temperature Sensor

    Install NGS scan tool to OBD-II data link connector. Turn ignition on. Access EGRT PID. Disconnect vacuum line to EGR valve. Apply vacuum to EGR valve. Observe EGRT PID voltage as vacuum is applied. If voltage changes from more than 1.0-4.5 volts to less than one volt, go to next step. If voltage is not as specified, replace EGR temperature sensor.

  23. 39) Check For Plugged EGR Modulator Valve

    Turn ignition off. Disconnect vacuum hoses from EGR modulator valve. Plug one port on top of valve and connect a vacuum pump to other port on top of valve. Apply vacuum. If vacuum does not hold, go to next step. If vacuum holds, replace valve. Repeat QUICK TEST .

  24. 40) Check EGR Modulator Valve

    Turn ignition off. Disconnect vacuum hoses from EGR modulator valve. Blow into exhaust pressure port. Plug one port on top of valve and apply vacuum to other port. If vacuum does not hold, replace valve. If vacuum holds, valve is okay. Go to TEST Z  for intermittent diagnosis.
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