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Test HC: Gasoline Fuel Delivery System: Testing

NOTE: Proceed to DTC testing steps listed in FAULT CODE SETTING CONDITION  table of fault code setting condition.
FAULT CODE SETTING CONDITION

Fault Code KOEO KOER Continuous Memory
P0148      HC1
    NOTE: For additional testing information, see DIAGNOSTIC AIDS .

  1. 1) For Continuous Memory Only DTC P0148: Check System Integrity
    This DTC indicates at least one bank lean at wide open throttle. Possible causes are:
    • Severely restricted fuel filter.
    • Severely restricted fuel supply line.

    Visually inspect complete fuel delivery system for damage. Check fuel lines, connections, relays, fuel tank, fuel pump, fuel pressure regulator, fuel pulse damper and fuel injector areas for leaks. Check for looseness, cracks, kinks, pinching, or abrasion caused by a collision or mishandling. Visually inspect electrical harness and connectors for loose pins, corrosion, abrasion, or other damage from collision or mishandling. Check electrical connectors for proper mating. Ensure customer has followed vehicle maintenance schedule. Ensure Inertia Fuel Shutoff (IFS) switch is reset. Ensure battery is fully charged (12.5 volts or more) and that fuses are okay. Ensure fuel level in tank is sufficient. Repair as necessary. If no faults are found, go to next step.

  2. 2) Check Voltage At Fuel Pump Harness Connector

    Connect battery charger to battery. Ensure IFS is reset. If it is not reset, perform INERTIA FUEL SHUTOFF SWITCH RESET PROCEDURE under GASOLINE SYSTEM under FUEL SYSTEM SAFETY PRECAUTIONS. Connect scan tool to Data Link Connector (DLC). Disconnect fuel pump harness connector at fuel pump. Turn ignition switch to ON position. Connect DVOM between fuel pump PWR and GND circuits at fuel pump harness connector. See WIRING DIAGRAMS . Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Command fuel pump ON and monitor DVOM voltage. If voltage is more than 12.5 volts, turn ignition switch to OFF position, exit OUTPUT TEST MODE, reconnect fuel pump harness connector and go to next step. If voltage is 12.5 volts or less, go to TEST KB, step 70) (ERFS vehicles), or check for open or shorts in fuel pump PWR or GND circuits (all others). See Figure.

  3. 3) Check Fuel Filter For Proper Maintenance

    Check last time fuel filter was replaced. If fuel filter has been serviced regularly (within 30,000 miles), go to next step. If fuel filter has not been serviced regularly, replace fuel filter and go to next step.
    4. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .
    NOTE: When energized by scan tool, fuel pump will operate for only 8 seconds.

  4. 4) Check Fuel Pressure
    Turn ignition switch to OFF position. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEMS in appropriate REMOVAL & INSTALLATION article. Install fuel pressure gauge supplied in Kit (134-00114) to Schrader valve located on fuel rail. Turn ignition switch to ON position. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Command fuel pump ON.

    Record fuel pressure. Compare fuel pressure to specification. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification on vehicles with returnable fuel system, go to next step. If fuel pressure is within specification on vehicles with ERFS, go to step  6). If fuel pressure is within specification on vehicles with MRFS, go to step  12). See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is not within specification, proceed as follows:

    • If fuel pressure is more than specified on vehicles with MRFS, replace fuel pressure regulator in fuel tank. Recheck fuel pressure.
    • If fuel pressure is less than specified on vehicles with MRFS, go to step  6).
    • If fuel pressure is more than specified on vehicles with ERFS, repeat QUICK TEST . Other DTCs should be present if fuel pressure concern exists.
    • If fuel pressure is more than specified on all other vehicles with returnable fuel system, go to step  10).
    • If fuel pressure is less than specified on all other vehicles with ERFS and returnable fuel system, go to step  13).

    5. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .

  5. 5) Check Fuel Pressure Leakdown
    With fuel pressure gauge supplied in Kit (134-00114) connected to Schrader valve located on fuel rail, turn ignition switch to ON position. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Command fuel pump ON. Record maximum fuel pressure. Turn ignition switch to OFF position. If fuel pressure remains within 5 psi (34 kPa) of maximum fuel pressure for one minute after fuel pump turns off, go to step  7). If fuel pressure does not remain within 5 psi (34 kPa) of maximum fuel pressure for one minute after fuel pump turns off, go to next step.

  6. 6) Check Pressure Regulator & Pulse Damper Diaphragm

    With fuel pressure gauge supplied in Kit (134-00114) connected to Schrader valve located on fuel rail, start engine and allow to idle for 10 seconds. Turn ignition switch to OFF position and wait 10 seconds. Start engine again and allow to idle for 10 seconds. Turn ignition switch to OFF position. Disconnect and inspect vacuum hose from fuel pressure regulator or pulse damper. If hose is wet with fuel, replace pulse damper (vehicles with MRFS), or fuel pressure regulator (all others). If hose is dry, go to step  13) (vehicles with MRFS), or go to step  12) (all others).

  7. 7) Check Fuel Pressure While Test Driving Vehicle

    Ensure fuel pressure gauge supplied in Kit (134-00114) is connected to Schrader valve located on fuel rail. Disconnect and plug fuel pressure regulator vacuum hose. Drive vehicle with heavy accelerations while monitoring fuel pressure gauge reading. If fuel pressure reading holds steady within 3 psi (21 kPa) during road test, go to next step. If fuel pressure reading does not hold steady within 3 psi (21 kPa) during road test, go to step  13).

  8. 8) Check Fuel Pressure Regulator Response

    Ensure fuel pressure gauge supplied in Kit (134-00114) is connected to Schrader valve located on fuel rail. Install vacuum gauge to intake manifold. Ensure fuel pressure and vacuum gauges can be seen by vehicle operator. Road test vehicle, accelerating and decelerating engine speed while monitoring fuel pressure and vacuum gauge readings. Fuel pressure gauge reading should increase as vacuum gauge reading decreases, and decrease as vacuum gauge reading increases. If gauge readings do not operate as specified, go to next step. If gauge readings operate as specified, fuel system is functioning properly. Diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE.

  9. 9) Check Vacuum Supply

    Turn ignition switch to OFF position. Ensure fuel pressure gauge supplied in Kit (134-00114) is connected to Schrader valve located on fuel rail. Disconnect and plug fuel pressure regulator vacuum hose. Install vacuum pump to fuel pressure regulator. Start engine and allow to idle. Observe fuel pressure gauge while applying vacuum to fuel pressure regulator. If fuel pressure reading changes as vacuum is applied, repair vacuum source to fuel pressure regulator. If fuel pressure reading does not change as vacuum is applied, replace fuel pressure regulator.
    10. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .

  10. 10) Check For Restricted Fuel Return Line
    Ensure fuel pressure gauge supplied in Kit (134-00114) is connected to Schrader valve located on fuel rail. Turn ignition switch to OFF position. Leave scan tool connected to DLC. Disconnect fuel return line at fuel rail and connect a separate hose to fuel rail and place opposite end of hose in clean, one quart container. Turn ignition switch to ON position. Using scan tool, command fuel pump ON to obtain maximum fuel flow. Observe fuel pressure and ensure fuel is being returned to one quart container from hose connected to fuel rail. One command of fuel pump ON is sufficient. Compare fuel pressure to specification. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification and fuel flows into one quart container, go to next step. If fuel pressure is not within specification and/or fuel does not flow into one quart container, replace fuel pressure regulator.
    11. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .

  11. 11) Check Fuel Return System
    Turn ignition switch to OFF position. Ensure fuel return line is disconnected at fuel rail. Disconnect fuel return line at fuel pump. Check return line for restrictions due to blockage, kinking or pinching. Apply 3-5 psi (21-34 kPa) compressed air to return line. If air flows freely through fuel return line, replace fuel pump module. If air does not flow freely through fuel return line, repair or replace fuel return line.
    12. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .

  12. 12) Check Fuel Injector Flow & Leakage
    Turn ignition switch to OFF position. Use Rotunda fuel injector tester supplied in Kit (134-00114) to flow test and leak test fuel injectors. Follow injector tester instructions. If tests for any fuel injector are not within specification, replace faulty fuel injector. If tests for each fuel injector are within specification on vehicles with EFRS or MRFS, check for additional symptoms and repair as necessary. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article. If tests for each fuel injector are within specification on vehicles with a returnable fuel system, check for leaks in fuel system. Repair as necessary. If no fuel system leaks exist, replace fuel pump.
    13. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .

  13. 13) Check Fuel Supply Line For Restriction
    Turn ignition switch to OFF position. Release fuel system pressure. Disconnect fuel supply line at fuel rail and at fuel pump. Check supply line for restrictions due to blockage, kinking or pinching. Apply 3-5 psi (21-34 kPa) compressed air to fuel supply line. If air flows freely through fuel supply line, replace fuel pump module. If air does not flow freely through fuel supply line, repair cause of restriction or replace fuel supply line.
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