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DTC P0172: 1/1 Fuel System Rich: Testing

NOTE: 1/1 HO2S may also be referred to as an upstream oxygen sensor. On 2.4L, 1/1 HO2S is located on exhaust manifold flange. On 3.3L and 3.8L, 1/1 HO2S is located on right exhaust manifold flange (manifold closest to firewall).
  1. Turn ignition on. Using scan tool, read DTCs. If Good Trip counter is displayed for DTC P0172 and displayed count is "0", go to next step. If Good Trip counter is not displayed for DTC P0172 or displayed count is not "0", go to step  15.
  2. Turn ignition off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Remove test port cap from fuel rail. Install a fuel pressure gauge to test port on fuel rail. Turn ignition on. Using scan tool, actuate ASD fuel system test. Allow fuel pressure gauge to stabilize. Stop ASD fuel system activation. Fuel pressure should be 53-63 psi (3.73-4.43 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is more than specified, replace pressure regulator. See FUEL SYSTEMS in appropriate REMOVAL, OVERHAUL & INSTALLATION article
  3. Turn ignition on. Using scan tool, read 1/1 HO2S voltage. If voltage is .4-.6 volt, go to next step. If voltage is not .4-.6 volt, go to step  11.
  4. Turn ignition off. Wait at least 10 minutes to allow HO2S to cool. Turn ignition on. Using scan tool in SENSOR mode, monitor 1/1 HO2S voltage until voltage stabilizes at .4-.6 volt. Using scan tool, actuate HO2S HEATER TEST and monitor 1/1 HO2S voltage for 2 minutes. If voltage does not stay at .4-.6 volt, go to next step. If voltage stays at .4-.6 volt, replace 1/1 HO2S.
  5. Turn ignition off. Disconnect EVAP purge solenoid hoses. EVAP purge solenoid is located on lower right side of engine compartment, near radiator. Using a vacuum pump, apply 10 in. Hg to EVAP purge solenoid vacuum source port. If vacuum holds, go to next step. If vacuum does not hold, replace EVAP canister purge solenoid valve.
  6. Turn ignition on. Using scan tool, read TP sensor voltage with throttle fully closed. If TP sensor voltage is .92 volt or less with throttle closed, go to next step. If TP sensor voltage is more than .92 volt with throttle closed, check throttle plate and linkage for binding. Repair throttle plate and linkage as necessary. If throttle plate and linkage are okay, replace TP sensor.
  7. Ensure ignition is on. Using scan tool, read TP sensor voltage while slowly opening and closing throttle. If TP sensor voltage changes smoothly while opening and closing throttle, go to next step. If TP sensor voltage does not change smoothly while opening and closing throttle, replace TP sensor.
  8. Turn ignition off. Connect a vacuum gauge to manifold vacuum source. Start engine and allow it to idle. If engine will not idle, maintain a constant. Using scan tool in SENSOR mode, monitor Manifold Absolute Pressure (MAP) vacuum value. Compare scan tool reading with vacuum gauge reading. If scan tool reading is within one in. Hg of vacuum gauge, turn ignition off and go to next step. If scan tool reading is not within one in. Hg of vacuum gauge reading, replace MAP sensor. MAP sensor contains a Black 3-pin connector.
    9. NOTE: For the following test to be valid, the thermostat must be operating properly. Test works best if performed on a cold engine (cold soak).
  9. Turn ignition on. Using scan tool, read ECT sensor value. If engine coolant temperature is more than 180°F (82°C), allow engine coolant temperature to cool down to 150°F (66°C) before proceeding. If engine coolant temperature is 150°F (66°C) or less, start engine and monitor scan tool until engine coolant temperature reaches 180°F (82°C). If ECT sensor value increases smoothly and reaches at least 180°F (82°C), go to next step. If ECT sensor value increase is erratic or does not reach at least 180°F (82°C), check for cooling system problems. Repair cooling system as necessary. If cooling system is okay, replace ECT sensor. ECT sensor is located on thermostat housing (2.4L) or is threaded into a coolant passage near thermostat housing (3.3L and 3.8L).
  10. Check the following additional items as possible mechanical problems:
    • Engine vacuum must be at least 13 in. Hg with shift selector in Neutral.
    • Engine valve timing must be within specification.
    • Engine compression must be within specification.
    • Engine exhaust system must be free of restrictions.
    • Engine Positive Crankcase Ventilation (PCV) system must flow freely.
    • Torque converter stall speed must be within specification.
    • Power brake booster must have no internal leaks.
    • Fuel must be free of contamination.
    • Fuel injectors must be free of restrictions.
    • Fuel injector control wires must be installed on correct injector.

    Repair any mechanical problems as necessary. If no mechanical problems exist, test is complete.

  11. Turn ignition on. Disconnect 1/1 HO2S connector. Using scan tool, read 1/1 HO2S voltage. If voltage is not .4-.6 volt, go to next step. If voltage is .4-.6 volt, replace 1/1 HO2S.
  12. Turn ignition off. Disconnect PCM connectors. PCM is located on left side of engine compartment, near front of battery. Inspect connectors for damaged pins, corrosion and loose terminals. Repair connectors as necessary. If connectors are okay, measure resistance of Dark Blue/Light Blue wire between 1/1 HO2S harness connector and terminal No. 30 at PCM C1 harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Dark Blue/Light Blue wire between PCM and 1/1 HO2S.
  13. Ensure ignition is off. Reconnect PCM connectors. Start engine and allow it to idle. Measure voltage between ground and Dark Blue/Light Blue wire at 1/1 HO2S harness connector. If voltage is .6 volt or less, go to next step. If voltage is more than .6 volt, repair short to voltage in Dark Blue/Light Blue wire between 1/1 HO2S and PCM.
  14. At this time, PCM is assumed to be defective. Replace PCM. Program the new PCM. See PROGRAMMING .
  15. At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Check for any contaminants that may have damaged the 1/1 HO2S, contaminated fuel, unapproved silicone, oil and coolant. Repair any problems that are found. If no problems are found, start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, monitor parameters related to DTC while wiggling connectors and wiring harness. If value changes while wiggling connectors and wiring harness, repair connectors and wiring harness where wiggling caused value to change. If value does not change, review Freeze Frame data using scan tool. Attempt to duplicate condition that caused DTC to set. Check for any related technical service bulletins that may apply. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. See WIRING DIAGRAMS article. If no problems are indicated, test is complete.
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