DTC P0171: 1/1 O2 Sensor Fuel System Lean Or DTC P0174: 2/1 O2 Sensor Fuel System Lean: Testing

Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant. Turn ignition on, engine not running. Using the DRBIII®, read DTCs. Is the Good Trip Counter displayed and equal to zero? If yes, go to next step. If no, go to step 17.

WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. See FUEL SYSTEM PRESSURE RELEASE .

Release fuel system pressure. Install a fuel pressure gauge to the fuel rail. Turn ignition on, engine not running. Using the DRBIII®, actuate the Auto Shut Down (ASD) fuel system test and observe the fuel pressure gauge. Fuel pressure specification is 44.2-54.2 psi (305-373 kPa). Turn the ignition off. If fuel pressure is less than specification, go to next step. If fuel pressure is within specification, go to step 6. If fuel pressure is greater than specification, replace the Fuel Pressure Regulator and Fuel Filter.
Raise and support vehicle. Release fuel system pressure. Disconnect the fuel pressure line at the fuel pump module. Connect Fuel Line Adapter (No. 6539 5/16" or No. 6631 3/8") between disconnected fuel line and the fuel pump module. Attach a fuel pressure test gauge to the "T" fitting on the fuel line adapter. Turn ignition on, engine not running. Using the DRBIII®, actuate the ASD Fuel System Test and observe the fuel pressure gauge. Fuel pressure specification is 44.2-54.2 psi (305-373 kPa). Turn the ignition off. Is the fuel pressure within specification? If yes, repair or replace fuel supply line as necessary. If no go to next step.
Release fuel system pressure. Remove the fuel pump module and inspect the fuel inlet strainer. See Figure. Is the fuel inlet strainer plugged? If yes, replace the Fuel Pump Inlet Strainer. If no, go to next step.
There are no possible causes remaining, replace the Fuel Pump Module.

NOTE: The fuel pressure must be within specification before continuing.

Release fuel system pressure. Disconnect the fuel supply line at the fuel rail. Connect Fuel Line Adapter (No. 6539 5/16" or No. 6631 3/8") to the disconnected fuel supply line. Insert the other end of the adapter into a graduated container. DO NOT operate the fuel pump for more than 7 seconds. Fuel pump module reservoir may run empty and damage to the fuel pump will result. A good fuel pump will deliver at least 1/4 liter (1/2 pint) of fuel in 7 seconds. Turn ignition on, engine not running. Using the DRBIII®, actuate the ASD Fuel System test for 7 seconds. Is the fuel pump volume within specification? If yes, go to next step. If no, check for a kinked/damaged fuel supply line between the fuel tank and fuel rail. If okay, replace the Fuel Pump Module.
Turn the ignition off. Wait a minimum of 10 minutes to allow the O2 Sensor and exhaust system to cool down before continuing the test. Turn ignition on, engine not running. Using the DRBIII®, read the O2 Sensor voltage. Is the voltage greater than 4.5 volts? If yes, go to next step. If no, go to step 14.
Turn the ignition off. Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Turn ignition on, engine not running. Using the DRBIII®, actuate the O2 Heater Test. Using the DRBIII®, monitor O2 Sensor voltage for at least 2 minutes. Does the voltage stay greater than 4.5 volts? If yes, replace the O2 Sensor. If no, go to next step.
Using the DRBIII®, read TP Sensor voltage. The throttle must be against the stop. Is the voltage 0.92 volt or less with the throttle closed? If yes, go to next step. If no, check for a binding throttle condition. If okay, replace the TP Sensor.
Using the DRBIII®, continue to read the TP Sensor voltage. While monitoring the DRBIII®, slowly open the throttle to Wide Open Throttle (WOT) position, then slowly close the throttle. Does the TP Sensor voltage increase and decrease smoothly? If yes, go to next step. If no, replace the TP Sensor.
Turn the ignition off. Connect a vacuum gauge to a manifold vacuum source. Start the engine. Allow the engine to idle. If engine will not idle, maintain a constant RPM above idle. Using the DRBIII®, read the MAP Sensor vacuum value. Is the DRBIII® reading within 1 in. Hg of the vacuum gauge reading? If yes, go to next step. If no, replace the MAP Sensor.

NOTE: For this test to be valid, the thermostat must be operating correctly. This test works best if performed on a cold engine (cold soak).

Turn ignition on, engine not running. Using the DRBIII®, read the Engine Coolant Temperature (ECT) Sensor value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature. If engine coolant temperature is above 180°F (82°C), allow the engine to cool until 150°F (65°C) is reached. Start the engine. During engine warm-up, monitor the ECT Sensor value. The temperature value change should be a smooth transition from start up to normal operating temp 180°F (82°C). The value should reach at least 180°F (82°C). Did the ECT value increase smoothly and did it reach at least 180°F (82°C)? If yes, go to next step. If no, replace the ECT Sensor.
Check for any of the following conditions/mechanical problems:
- Air induction system must be free from leaks.
- Engine vacuum must be at least 13 in. Hg in Neutral.
- Engine valve timing must be within specifications.
- Engine compression must be within specifications.
- Engine exhaust system must be free of any restrictions or leaks.
- Positive Crankcase Ventilation (PCV) system must flow freely.
- Torque converter stall speed must be within specifications.
- Power brake booster must be free of any internal vacuum leaks.
- Fuel must be free of contamination.
- Fuel Injectors must not be plugged or restricted and Fuel Injector/control wires must not be connected to an incorrect Fuel Injector.
Are there any engine mechanical problems? If yes, repair as necessary. If no, go to step 17.
Turn the ignition off. Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Disconnect the O2 Sensor harness connector. Turn ignition on, engine not running. Using the DRBIII®, monitor the O2 Sensor voltage. Is the O2 Sensor voltage greater than 4.5 volts? If yes, replace the O2 Sensor. If no, go to next step.
Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance between ground and the O2 Sensor Signal circuit at the PCM harness connector. Is the resistance less than 100 ohms? If yes, repair the short to ground in the O2 Sensor Signal circuit. If no, go to next step.
There are no possible causes remaining, replace and program the Powertrain Control Module.

WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.

Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant. The conditions that set the DTC are not present at this time. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.