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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 27 (Engine Controls - Self-Diagnostics - 2.5L) >> Diagnostic Tests >> DTC P0400: EGR Flow Malfunction >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform DTC confirmation procedure. See DTC CONFIRMATION PROCEDURE  under SELF-DIAGNOSTIC SYSTEM. Check for DTCs during KOEO or KOER self-test. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0400 is present, go to next step. If DTC P0400 is not present, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  2. Check EGR boost solenoid valve connector connection. Repair as necessary and check for any other DTC during KOEO or KOER self-test. If any other DTCs are present, go to appropriate test. If no other DTC is present, go to next step.
  3. Check for vacuum leaks in hoses connected to MAF sensor, hoses connected to throttle body, intake manifold gasket, PCV system, other vacuum hoses (disconnected) or loose engine dipstick. Also check for exhaust leaks at flanges or gaskets. Repair as necessary and go to step  17 . If no leaks are found, go to next step.
  4. Using compression gauge, check cylinder compression. Minimum cylinder compression should be 141 psi (8.4 kg/cm2 ) at 250 RPM and maximum difference between cylinders should be 28 psi (2.0 kg/cm2 ). If cylinder compression is not okay, repair engine as necessary and go to step  17 . If compression is okay, go to next step.
  5. Turn ignition on. Listen for click (initialization noise) from EGR valve. EGR valve initialization is closing action of EGR valve before and after engine is turn on and off. If noise can be heard, go to step  11 . If noise cannot be heard, go to next step.
  6. Turn ignition off. Disconnect EGR valve connector. Turn ignition on. Measure voltage between ground and EGR valve harness connector terminals "C" (Red/Black wire) and "D" (Red/Black wire), individually. See Fig 1 . If more than 10.5 volts is present, go to next step. If 10.5 volts or less are present, repair appropriate open circuit. See WIRING DIAGRAMS article. Go to step  17 .
  7. Turn ignition off. Measure resistance between EGR valve connector terminals "C" (Red/Black wire) and terminals "A" (Red/Yellow wire) and "E" (Green wire), individually. See Fig 1 . Also measure resistance between EGR valve connector terminals "D" (Red/Black wire) and terminals "B" (Pink/Black wire) and "F" (Orange/Black wire), individually. Resistance for each measurement should be about 22 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace EGR valve and go to step  17 .
  8. Disconnect PCM connector. Check for damaged or corroded PCM connector terminals. Repair as necessary, and go to step  17 . If connector terminals are okay, go to next step.
  9. Leave ignition off and EGR valve harness connector disconnected. Measure resistance between PCM harness connector terminals and corresponding terminal at EGR valve harness connector. See Figure and Fig 1 . See EGR CIRCUIT IDENTIFICATION  table. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair appropriate open circuit. See WIRING DIAGRAMS article. Go to step  17 .
    EGR CIRCUIT IDENTIFICATION

    EGR Connector Terminals PCM Connector Terminals No.
    A (Red/Yellow wire) 72 (Red/Yellow wire)
    B (Purple/Black wire) 46 (Purple/Black wire)
    E (Green wire) 68 (Green wire)
    F (Orange/Black wire) 56 (Orange/Black wire)
  10. Leave ignition off and EGR valve disconnected. Measure resistance between PCM harness connector terminals No. 46 (Pink/Black wire), 56 (Orange/Black wire), 68 (Green wire) and 72 (Red/Yellow wire), and terminals No. 51 (Black/Blue wire), 91 (Black/Yellow wire) and 103 (Black/Red wire), individually. Measure resistance between PCM harness connector terminals No. 46 (Pink/Black wire), 56 (Orange/Black wire), 68 (Green wire) and 72 (Red/Yellow wire), and terminals No. 71 (Red/Black wire), 90 (Gray/Red wire) and 97 (Red/Black wire), individually. If each measurement is more than 10 k/ohms, replace EGR valve and go to step  17 . If any measurement is 10 k/ohms or less, go to next step.
  11. Turn ignition off. Disconnect EGR boost solenoid valve connector. Turn ignition on. Measure voltage between EGR boost solenoid valve harness connector Red/Black terminal and chassis ground. If more than 10.5 volts is present, go to next step. If 10.5 volts or less are present, repair open circuit. See WIRING DIAGRAMS article. Go to step  17 .
  12. Turn ignition off. Measure resistance between EGR boost solenoid valve connector terminals. If resistance is 30-70 ohms, go to next step. If resistance is not 30-70 ohms, replace EGR boost solenoid valve and go to step  17 .
  13. Disconnect PCM connector. Check for damaged or corroded PCM connector terminals. Repair as necessary, and go to step  17 . If connector terminals are okay, go to next step.
  14. Measure resistance between PCM harness connector terminal No. 98 (White/Red wire) and EGR boost solenoid valve harness connector White/Red wire terminal. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open White/Red wire. See WIRING DIAGRAMS article. Go to step  17 .
  15. Measure resistance between PCM harness connector terminals No. 98 (White/Red wire), and terminals No. 51 (Black/Blue wire), 91 (Black/Yellow wire) and 103 (Black/Red wire), individually. Measure resistance between PCM harness connector terminals No. 98 (White/Red wire), and terminals No. 71 (Red/Black wire), 90 (Gray/Red wire) and 97 (Red/Black wire), individually. If each measurement is more than 10 k/ohms, go to next step. If any measurement is 10 k/ohms or less, repair appropriate circuit and go to step  17 .
  16. Reconnect PCM and EGR boost solenoid valve connections. Disconnect vacuum hose, located between EGR boost sensor solenoid valve and intake manifold, from EGR boost solenoid valve. Connect vacuum pump to EGR boost solenoid valve and apply 10 in. Hg to EGR boost solenoid valve. Disconnect vacuum hose, located between EGR boost solenoid valve and EGR boost sensor, from EGR boost sensor. Ensure vacuum hose is not damaged. Repair as necessary. If vacuum hose is okay, install vacuum gauge to end of vacuum hose. Turn ignition on. Backprobing, momentarily connect a fused jumper wire between PCM connector terminal No. 98 (White/Red wire) and ground. See Figure . Again apply 10 in. Hg to EGR boost solenoid valve. Again, momentarily connect a fused jumper wire between PCM connector terminal No. 98 (White/Red wire) and ground. Turn ignition off. If vacuum signal is indicated (at any time), problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If vacuum signal is not indicated, replace EGR boost solenoid valve and go to next step.
  17. Reconnect all connections. Turn ignition on. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Using scan tool, perform OBD II drive mode. See DRIVE MODES  under SELF-DIAGNOSTIC SYSTEM. Using scan tool, access DIAGNOSIS MONITORING TEST RESULTS. Monitor TEST #10:4C:31. If measured value is within specification, replace PCM and go to next step. See REMOVAL, OVERHAUL & INSTALLATION article. On vehicles equipped with immobilizer system, reprogram ignition key identification numbers. See COMPUTER RELEARN PROCEDURES - IMPORT article in GENERAL INFORMATION. If measured value is not within specification, go to next step.
  18. Perform DTC confirmation procedure. See DTC CONFIRMATION PROCEDURE  under SELF-DIAGNOSTIC SYSTEM. See DTC CONFIRMATION PROCEDURE  under SELF-DIAGNOSTIC SYSTEM. See DTC CONFIRMATION PROCEDURE  under SELF-DIAGNOSTIC SYSTEM. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to appropriate test.
Fig 1: Identifying EGR Valve Harness Connector Terminals
G00020981Courtesy of MAZDA MOTORS CORP.
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