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Home >> Mazda >> 2002 >> MX-5 Miata Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0172: Fuel Trim System Too Rich >> Diagnostic Procedure

Diagnostic Procedure

  1. Turn ignition off. Connect New Generation Star (NGS) tester or equivalent to OBD-II Data Link Connector-2 (DLC-2). See Figure. Turn ignition on. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check for service bulletins and/or other line of repair information related to this DTC. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  10. If repair information is not available, go to next step.
  2. Monitor for DTC or pending coderelated to this DTC. If other DTC is present, follow appropriate DTC diagnostic procedure. If no other DTC is set, but driveability concern or rough idle is present, go to step  9. If no other DTC is set and no driveability concern or rough idle is present, go to next step.
  3. Check for triggered DTC on recorded FREEZE FRAME DATA. If malfunction code recordedis P0172, go to next step. If malfunction code recordedis different that P0172, follow appropriate DTC diagnostic procedure.
  4. Start engine and let it idle until it reaches normal operation temperature. Using NGS tester or equivalent, access ECT, MAF, TP, and VSS PIDs. For system PID specifications. See SYSTEMS INPUT SIGNAL SPECIFICATIONS  table. If all systems input voltages are as specified, go to next step. If any system input voltage is not as specified, inspect system sensor and system wiring harness, repair or replace as necessary. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to step  10
  5. Inspect same PIDs while simulating recorded FREEZE FRAME DATA conditions, If no input signal is drastically change, go to next step. If any input signal is drastically change, inspect system sensor and system wiring harness, repair or replace as necessary and go to step  10.
  6. With engine running at idle and at normal operation temperature. Using NGS tester or equivalent, access O2S11 PID. Verify O2S11 PID while racing engine (in PARK). Ensure that each value is within following conditions:
    • More than 0.45 volts. when suddenly depressing accelerator pedal (rich condition).
    • Less than 0.45 volts. just after release of accelerator pedal (lean condition).

    If O2S11 PIDs readings are as specified, go to next step. If any O2S11 PID reading is not as specified, inspect for exhaust leak between exhaust manifold and front H2OS. If exhaust leak is found, repair as necessary and repeat this test, If exhaust leak is not found, replace front H2OS. After repair, go to step  10.

  7. Turn ignition off and perform fuel pressure test. Release fuel pressure from fuel system. Install fuel pressure gauge. For proper fuel pressure test. See FUEL PRESSURE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Fuel pressure should be 53-61 psi (3.7-4.3 kg/cm2 ). If fuel pressure is as specified, go to step  9. If fuel pressure is not as specified, go to next step.
  8. Turn ignition on. Perform fuel pump maximum pressure test. See FUEL PUMP MAXIMUM PRESSURE INSPECTION under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Fuel pump maximum pressure should be 92 psi (6.5 kg/cm2 ). If fuel pressure is not as specified, check as follow:
    • If fuel pump maximum pressure is less than 92 psi (6.5 kg/cm2 ). Check fuel pump circuit for open or poor connection, repair or replace connector or circuit as necessary and go to step  10.
    • If connector and circuits are okay, but fuel pump maximum pressure is less than 92 psi (6.5 kg/cm2 ),replace fuel pump and go to step  10.
    • If connector and circuits are okay, but fuel pump maximum pressure is more than 92 psi (6.5 kg/cm2 ), replace fuel pressure regulator and go to step  10.
    • If fuel pump maximum fuel pressure is as specified, go to next step.
  9. Turn ignition off. Disconnect both vacuum hoses from Purge Control Solenoid Valve (PCSV). Blow air through PCSV vacuum hose fitting. If air does not flow through valve, go to next step. If air flows through valve, replace PCSV. After repair, go to next step.
  10. Return vehicle to original condition. Using NGS tester or equivalent, clear DTCs from PCM memory. Start engine and run DRIVE MODE 1, 2 and 3. See DRIVE MODES  under SELF-DIAGNOSTIC SYSTEM.Monitor for pending DTCs. If same DTC P0171 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. If any other DTC is present, follow appropriate DTC diagnostic procedure.
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