DTC P0172: Fuel System 1/1 Rich Or DTC P0175: Fuel System 2/1 Rich: Testing

NOTE: Before proceeding, check for contaminants that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.

Ignition on, engine not running. With the DRBIII® scan tool, read DTCs and record the related freeze frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, see INTERMITTENT CONDITION under SELF-DIAGNOSTIC SYSTEM.

WARNING: Fuel system is under constant pressure even when ignition is off. Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be releases.

Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Connect fuel pressure gauge. Ignition on, engine not running. With the DRBIII® scan tool, actuate ASD fuel system test and observe fuel pressure gauge. Fuel pressure should be 53-63 psi (365-434 kPa). Turn ignition off. If fuel pressure is within specification, stop all actuations and go to next step. If fuel pressure is greater than specification, stop all actuations. Replace fuel filter/pressure regulator.

NOTE: If one of the O2 sensors signal or return circuits are shorted to ground or voltage, all the other O2 sensor voltage readings will be affected. After the repairs have been made, verify proper O2 sensor operation. If all the O2 sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining O2 sensors.

Start the engine. Allow the engine to reach normal operating temperature. With the DRBIII® scan tool, read the O2 sensor voltage. Is the voltage switching between 2.5 volts and 3.4 volts? If yes, go to next step. If no, go to step 9.
Turn the ignition off. Allow the O2 sensor to cool down before continuing the test. Allow the O2 sensor voltage to stabilize at 5.0 volts. Raising the hood may help in reducing the under hood temperatures. Ignition on, engine not running. With the DRBIII® scan tool, actuate the O2 heater test. With the DRBIII® scan tool, monitor O2 sensor voltage for at least 2 minutes. Does the voltage stay above 4.5 volts? If yes, replace the O2 sensor. If no, go to next step.
Turn the ignition off. Disconnect the hoses at the EVAP purge solenoid. Using a hand vacuum pump, apply 10 in. Hg of vacuum to the EVAP purge solenoid vacuum source port on the component side. Did the EVAP purge solenoid hold vacuum? If yes, go to next step. If no, replace the EVAP purge solenoid.
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. With the DRBIII® scan tool in sensors, read the MAP sensor vacuum value. Is the DRBIII® scan tool reading within 1 in. Hg of the vacuum gauge reading? If yes, go to next step. If no, replace the MAP sensor.
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 the ignition on. With the DRBIII® scan tool, read the 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 value. The temp 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 a smooth transition 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:
- Ensure air intake system is free from leaks.
- Ensure engine vacuum is at least 13 in. Hg at idle in Park or Neutral.
- Ensure valve timing is correct.
- Ensure engine compression is within specification.
- Ensure exhaust system is free from restrictions or leaks.
- Ensure PCV system flows freely.
- Ensure torque converter stall speed is within specification.
- Ensure power brake booster has no internal vacuum leaks.
- Ensure fuel is not contaminated.
- Ensure fuel injectors are not restricted.
- Ensure fuel injector harness connectors are connected to correct fuel injectors.
Are there any engine mechanical problems? If yes, repair as necessary. If no, test is complete.
Ignition on, engine not running. Disconnect the O2 sensor harness connector. With the DRBIII® scan tool, monitor the O2 sensor voltage. The O2 sensor voltage should read 5.0 volts on the DRBIII® scan tool with the connector disconnected. Using a jumper wire, jump across the O2 sensor harness connector from the O2 signal circuit to the O2 return circuit at the O2 sensor harness connector. The voltage should drop from 5.0 volts to 2.5 volts with the jumper wire in place. Did the O2 sensor volts change from 5.0 volts to 2.5 volts? If yes, replace the O2 sensor. If no, go to next step.
Turn the ignition off. Disconnect the O2 sensor harness connector. Turn the ignition on. Measure the voltage of the O2 signal circuit in the O2 sensor harness connector. Is the voltage above 4.8 volts? If yes, check the O2 signal circuit for damage, short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the PCM. See PROGRAMMING . If no, go to next step.
Turn the ignition off. Disconnect the O2 sensor harness connector. Turn the ignition on. Measure the voltage on the O2 return circuit in the O2 sensor harness connector. Is the voltage at 2.5 volts? If yes, visually inspect both the component and the PCM connectors. Look for damage, partially broken wires and backed out or corroded terminals. If OK, replace and program the PCM. See PROGRAMMING . If no, check the O2 return circuit for damage, short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the PCM. See PROGRAMMING .