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P0172






P0172-FUEL SYSTEM 1/1 RICH

Special Tools:






For a complete wiring diagram, refer to the Wiring Information.





Theory of Operation

The Oxygen Sensors (O2 Sensor) are used for fuel control and catalyst monitoring. Each O2 Sensor measures the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 Sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 Sensor heats the sensor to bring it to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 Sensor heats up and begins to generate a voltage within a range of 0-1,275 mV. Once sufficient O2 Sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 Sensor voltage to determine the air-to-fuel ratio. An O2 Sensor voltage that increases toward 1,000 mV indicates a rich fuel mixture. An O2 Sensor voltage that decreases toward 0 mV indicates a lean fuel mixture. The Powertrain Control Module (PCM) makes short term and long term fuel corrections to maintain stoichiometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on upstream O2 Sensor output and is designed for quick engine response. The long term fuel correction compensated for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich and lean conditions over a longer period of time.

- When Monitored:
With the engine running in closed loop mode, the ambient/battery temperature above -6.7°C (20°F) and altitude below 2590.8 m (8500 ft).

- Set Condition:
If the Powertrain Control Module (PCM) multiplies short term compensation by long term adaptive and a purge fuel multiplier and the result is below a certain value for 30 seconds over two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored. Two Trip Fault. Three good trips to turn off the MIL.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

Diagnostic Test

1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)

NOTE: Check for contaminates that may have damaged an O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.

1. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. With the scan tool, read DTCs.

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.

Is the DTC Active or Pending at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. CHECKING FUEL PRESSURE

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. Failure to follow these instructions can result in possible serious or fatal injury.

1. Turn the ignition off.
2. Install the Fuel Pressure Decay Tester (8978A) to the fuel rail.
3. Ignition on, engine not running.
4. Using the scan tool, actuate the Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification: 400 kPa +/- 14 kPa (58 psi +/- 2 psi).

5. Turn the ignition off.

Choose a conclusion that best matches your fuel pressure reading.

Within Specification

- Go To 3

Above Specification

- Replace the fuel filter/pressure regulator.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

CAUTION:
Before Proceeding Stop All Actuations.

3. O2 SENSOR OPERATION
1. Start the engine.
2. Allow the engine to reach normal operating temperature.

NOTE: If one of the O2 Sensors Signal or Return circuit is shorted to ground or voltage, all the other O2 Sensor voltage readings will be affected.

NOTE: 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.

3. Using the scan tool, monitor the O2 Sensor 1/1 voltage reading.

Is the voltage switching between 0 and 1 Volts?

Yes

- Go To 4

No

- Go To 9

4. 1/1 O2 SENSOR HEATER OPERATION
1. Turn the ignition off.

NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize at 5.0 Volts.

2. Ignition on, engine not running.
3. Using the scan tool, perform the 1/1 O2 Heater Test.
4. Using the scan tool, monitor the O2 Sensor voltage while performing the Heater test for at least two minutes.

Does the voltage stay above 0.8 Volt during the Heater test?

Yes

- Verify that there is good pin to terminal contact in the O2 Sensor and Powertrain Control Module connectors. Replace the 1/1 O2 Sensor if no problems were found with the connectors. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 5

5. MAP SENSOR OPERATION
1. Ignition on, engine not running.
2. With the scan tool, read the Barometric Pressure.

NOTE: The Barometric Pressure should be approximately equal to the actual barometric pressure. If necessary, compare the Barometric Pressure value of this vehicle to the value of a known good vehicle of a similar make and model.

3. Turn the ignition off.
4. Connect a Vacuum Gauge to a Manifold Vacuum source.
5. Start the engine.
6. Allow the engine to idle.

NOTE: If engine will not idle, maintain a constant RPM above idle.

7. With the scan tool, read the MAP Sensor vacuum value.

Is the scan tool reading for MAP Vacuum within 1 inch of the Vacuum Gauge reading and is the Barometric Pressure reading of the vehicle the approximately the same as actual Barometric Pressure?

Yes

- Go To 6

No

- Verify that there is good pin to terminal contact in the MAP Sensor and Powertrain Control Module connectors. Replace the MAP Sensor if no problems were found with the connectors. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

NOTE: Remove the vacuum gauge before continuing.

6. ECT SENSOR OPERATION

NOTE: For this test to be valid, the thermostat must be operating correctly.

NOTE: This test works best if performed on a cold engine (cold soak)

1. Ignition on, engine not running.
2. With the scan tool, read the Engine Coolant Temperature 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.

NOTE: If engine coolant temperature is above 82°C (180°F), allow the engine to cool until 65°C (150° ) is reached.

3. Start the Engine.
4. During engine warm-up, monitor the Engine Coolant Temperature value. The temp value change should be a smooth transition from start up to normal operating temp 82°C (180°F). The value should reach at least 82°C (180°F).

Did the ECT value increase smoothly and reach at least 82°C (180°F)?

Yes

- Go To 7

No

- Verify that there is good pin to terminal contact in the ECT Sensor and Powertrain Control Module connectors. Replace the Engine Coolant Temperature Sensor if no problems were found with the connectors. Engine Coolant Temperature Sensor - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

7. EVAP PURGE SOLENOID OPERATION
1. Turn the ignition off.
2. Disconnect the hoses at the Evap Purge Solenoid.
3. Using a hand vacuum pump, apply 10 inches of vacuum to the Evap Purge Solenoid vacuum source port on the component side.

Did the Evap Purge Solenoid hold vacuum?

Yes

- Go To 8

No

- Verify that there is good pin to terminal contact in the Solenoid and Powertrain Control Module connectors. Replace the Evap Purge Solenoid if no problems were found with the connectors.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

NOTE: Connect the vacuum hoses before continuing.

8. ENGINE MECHANICAL
1. Check for any of the following conditions/mechanical problems.
- AIR INDUCTION SYSTEM - must be free from leaks.
- ENGINE VACUUM - must be at least 13 inches 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.
- ENGINE PCV SYSTEM - must flow freely
- TORQUE CONVERTER STALL SPEED - must be within specifications
- POWER BRAKE BOOSTER - no internal vacuum leaks
- FUEL - must be free of contamination
- FUEL INJECTOR - plugged or restricted injector; control wire not connected to correct injector

Are there any engine mechanical problems?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 12

9. 1/1 O2 SENSOR

NOTE: Perform the following test on the O2 Sensors whose voltage was not switching properly in the previous step.

1. Ignition on, engine not running.
2. Disconnect the 1/1 O2 Sensor harness connector.
3. With the scan tool, monitor the 1/1 O2 Sensor voltage.
4. O2 Sensor voltage should read between 4.1 and 5.0 Volts on the scan tool with the connector disconnected.
5. Connect a jumper wire between the O2 Sensor 1/1 Signal circuit and the O2 Return Upstream circuit in the O2 Sensor harness connector.

NOTE: The voltage should drop from between 4.1 and 5.0 Volts down to 2.5 Volts with the jumper wire connected.

Did the O2 Sensor voltage drop from between 4.1 and 5.0 Volts to 2.5 Volts when the jumper wire was installed?

Yes

- Verify that there is good pin to terminal contact in the O2 Sensor and Powertrain Control Module connectors. Replace the 1/1 O2 Sensor if no problems were found with the connectors. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 10

NOTE: Remove the jumper wire before continuing.


10. O2 SENSOR 1/1 SIGNAL CIRCUIT
1. Measure the voltage on the O2 Sensor 1/1 Signal circuit in the O2 Sensor harness connector.

Is the voltage between 4.1 and 5.0 Volts?

Yes

- Go To 11

No

- Check the O2 Sensor 1/1 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 Powertrain Control Module. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

11. O2 SENSOR RETURN UPSTREAM CIRCUIT
1. Measure the voltage on the O2 Return Upstream circuit in the 1/1 O2 Sensor harness connector.

Is the voltage at 2.5 Volts?

Yes

- Go To 12

No

- Check the O2 Return Upstream 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 Powertrain Control Module. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

NOTE: Turn the ignition off before continuing.


12. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Sensors and the Powertrain Control Module (PCM).
- Look for any chafed, pierced, pinched or partially broken wires.
- Look for broken, bent, pushed out or corroded terminals.
- Verify that there is good pin to terminal contact in the 1/1 O2 Sensor and Powertrain Control Module connectors.
- Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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