P0171
P0171-FUEL SYSTEM 1/1 LEAN
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 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 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.
1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)
NOTE: Check for contaminants that may have damaged an O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.
1. Diagnose all other trouble codes before continuing.
2. Start the engine.
3. Allow the engine to reach normal operating temperature.
4. With a scan tool, select View 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.
NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).
1. Turn the ignition off.
2. Install the Fuel Pressure Decay Tester 8978 to the fuel rail.
3. Ignition on, engine not running.
4. With a scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.
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.
Below Specification
- Go To 13 CAUTION: Before Proceeding Stop All Actuations.
3. CHECKING THE EXHAUST SYSTEM FOR LEAKS
WARNING: The normal operating temperature of the exhaust system is very high. Never work around or attempt to service any part of the exhaust system until it has cooled. Special care should be taken when working near the catalytic converter. The temperature of the converter rises to a high level after a short period of engine operating time
CAUTION: Adjust the Air Pressure Regulator to 27.6 kPa (4 psi).
1. Turn the ignition off.
2. Raise the vehicle.
3. Connect Exhaust Cone 8404-EC or 8404-EC to Air Pressure Regulator (with hose) W-18-MIL-1146AS.
4. Insert the exhaust cone into the vehicle tail pipe.
5. If the vehicle is equipped with dual exhaust, use the 8404-ECT with equipped attached plug, and plug one side of the dual exhaust pipe. Pressurize the other as described above.
6. Apply SNOOP leak finder liquid or a mixture of liquid dish soap and water to the following areas:
- All welded joints from the exhaust manifold to 152.4 mm (6 inches) behind the downstream O2 sensor
- O2 sensor seal points
- O2 sensor boss welds
- Flange/joint connection(s)
- Exhaust manifold to cylinder head connection(s)
- EGR solenoid gasket base and tube seal points (if equipped)
7. Watch for the liquid/soapy water to bubble.
8. Use the following definitions to help determine if system or component repair/replacement is necessary:
Type 1 Leak is defined as a leak where very small foam like bubbles 1 mm (0.04 of an inch) or less appear.
Any Type 1 or greater leaks found in welded joints, O2 sensor seal points or O2 sensor boss welds must be repaired or the component must be replaced.
Type 2 Leak is defined as a leak where larger bubbles pea size, 8 mm (0.3 of an inch) or greater appear.
Any Type 2 or greater leaks found in flange or joint connections, exhaust manifold to cylinder head connections, or EGR gasket and tube seal points must be repaired or the components must be replaced.
9. If a leak is found that matches the above definition, repair or replace the component as necessary.
10. Once the repair is complete, repeat the procedure to verify that all leaks have been repaired.
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 4
4. O2 SENSOR OPERATION
NOTE: If one of the O2 Sensor's Signal or Return circuit is shorted to ground the scan tool will display all O2 Sensor voltage readings low. The O2 Sensor that is shorted to ground will display a voltage reading near or at 0 Volts.
NOTE: If one of the O2 Sensor Signal or Return circuits are shorted to voltage, the scan tool will display all O2 Sensor voltage readings high.
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.
1. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. With a scan tool, monitor all of the O2 Sensor voltage readings.
Is the voltage switching between 2.5 and 3.4 Volts for all the O2 Sensors?
Yes
- Go To 5
No
- Go To 9
5. 1/1 O2 SENSOR HEATER OPERATION
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.
1. Turn the ignition off.
2. Ignition on, engine not running.
3. With a scan tool, actuate the 1/1 O2 Heater Test.
4. Using the scan tool, monitor 1/1 O2 Sensor voltage for at least two minutes.
Does the voltage stay above 4.5 Volts?
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 6
6. MAP SENSOR OPERATION
NOTE: The Barometric Pressure should be approximately equal to the actual barometric pressure. If necessary, compare the value to the value of a known good vehicle of a similar make and model.
NOTE: If engine will not idle, maintain a constant RPM above idle.
1. Ignition on, engine not running.
2. With a scan tool, read the Barometric Pressure.
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.
7. Using the scan tool, read the MAP Sensor vacuum value.
Is the scan tool reading within 1" of Hg on the Vacuum Gauge reading and the barometric pressure comparable to a know good vehicle?
Yes
- Go To 7
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.
7. 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)
NOTE: If engine coolant temperature is above 82° C (180° F), allow the engine to cool until 65° C (150° F) is reached.
1. Ignition on, engine not running.
2. With a 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.
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 8
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.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
8. 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 12
9. 1/1 O2 SENSOR
NOTE: The voltage should drop from between 4.1 and 5.0 Volts to 2.5 Volts with the jumper wire in place.
1. Ignition on, engine not running.
2. Disconnect the 1/1 O2 Sensor harness connector.
3. With a 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 (K41) Signal circuit and the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.
Did the O2 Sensor voltage change from between 4.1 and 5.0 Volts to 2.5 Volts with the jumper wire 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. (K41) O2 SENSOR 1/1 SIGNAL CIRCUIT
1. With a scan tool, monitor the 1/1 O2 Sensor voltage reading with the jumper wire removed.
NOTE: The scan tool will display all O2 Sensor voltage readings approximately 5.0 Volts when only one O2 Sensor's Signal circuit is shorted to voltage.
NOTE: The scan tool will display one O2 Sensor voltage close to zero and the others will read lower than normal when one O2 Sensor Signal circuit contains excessive resistance.
Is the voltage between 4.1 and 5.0 Volts?
Yes
- Go To 11
No
- Check the (K41) O2 Sensor 1/1 Signal circuit for a 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. (K902) O2 RETURN UPSTREAM CIRCUIT
1. Measure the voltage on the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.
Is the voltage at 2.5 Volts?
Yes
- Go To 12
No
- Check the O2 Return circuit for a 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.
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).
2. Look for any chafed, pierced, pinched, or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Sensor and Control Module connectors.
4. 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.
13. 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 8978 between the fuel supply line and the fuel pump module.
4. Ignition on, engine not running.
5. With a scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.
NOTE: Fuel pressure specification is 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 14 CAUTION: Stop All Actuations.
14. FUEL PUMP INLET STRAINER
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.
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.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 15
15. FUEL PUMP MODULE
If there are no possible causes remaining, view repair.
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.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.