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P0174






P0174-FUEL SYSTEM 2/1 LEAN

Special Tools:










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

Theory of Operation

The fuel feedback system will maintain a stoichiometric fuel/air mixture, 14.7:1, by modifying the injector pulse width according to the oxygen content of the exhaust gas. 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 certain percentage is exceeded for 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. 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 (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.

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

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

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

Yes

- Go To 2

No

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

2. ACTIVE DTC
1. Diagnose all other DTCs before continuing.

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

2. Start the engine.
3. Allow the engine to reach normal operating temperature.
4. 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 3

No

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

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

NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

5. Turn the ignition off.

Choose a conclusion that best matches your fuel pressure reading.

Within Specification

- Go To 4

Above Specification (pressure too high)

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

Below Specification (pressure too low)

- Go To 9

4. CHECKING THE EXHAUST SYSTEM FOR LEAKS
1. Perform the CHECKING THE EXHAUST SYSTEM FOR LEAKS test procedure. Testing and Inspection.

Were any exhaust leaks found?

Yes

- Repair or replace the leaking exhaust parts as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 5

5. O2 SENSOR OPERATION
1. Perform the CHECKING THE OXYGEN SENSOR OPERATION test procedure. Checking The Oxygen Sensor Operation .
2.

Were any problems found with the O2 Sensors?

Yes

- Perform the appropriate repair.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 6

6. MAP SENSOR OPERATION
1. Perform the CHECKING THE MAP SENSOR OPERATION test procedure. Checking The MAP Sensor Operation .

Were any problems found with the MAP Sensor?

Yes

- Perform the appropriate repair.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 7

7. ENGINE MECHANICAL
1. Turn the ignition off.
2. 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 8

8. POWERTRAIN CONTROL MODULE (PCM)

NOTE: The most likely cause of this DTC is a fuel, ignition, or engine mechanical condition (low compression, vacuum leak, exhaust leak, etc.). Exhaust all other possibilities before replacing the Powertrain Control Module.

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

9. RESTRICTED FUEL SUPPLY LINE

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. Raise vehicle on hoist and disconnect the fuel pressure line at the fuel pump module.
3. Install Fuel Pressure Decay Tester (8978A) between the fuel supply line and the fuel pump module.
4. Turn the ignition on, engine not running.
5. With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification: 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Is the fuel pressure within specification?

Yes

- Repair or replace fuel supply line as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 10

CAUTION:
Stop All Actuations.

10. FUEL PUMP INLET STRAINER
1. Turn the ignition off.
2. Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.

Is the Fuel Inlet Strainer plugged?

Yes

- Replace the Fuel Pump Inlet Strainer. Fuel Pump Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 11

11. FUEL PUMP MODULE

Repair

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

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