Introduction

In cases where the Malfunction Indicator Lamp (MIL) on your vehicle’s dashboard is illuminated and the Engine Control Module (ECM) has stored DTC P0171 indicates the ECM has detected that one side of the engine (Bank 1) is running with too much air and insufficient fuel. This occurs when the engine takes in more air than it should in relation to the amount of fuel.

Symptoms of DTC P0171 include:

• Malfunction Indicator Lamp (MIL) ON or flashing

• Reduced engine power and performance

• Rough idling

• Engine misfire

• Poor fuel efficiency

Possible causes of this fault are:

• Weak fuel pump

• Faulty fuel injectors

• Faulty Mass Air Flow sensor

• Exhaust Gas Recirculation problems

• Faulty fuel pressure regulator

• Faulty positive crankcase ventilation

When DTC P0171 is present on a 2015 GMC Yukon V8, 5.3L, replacing the fuel pump may resolve the issue.

Initial Inspection

During your initial inspection, check for obvious mechanical signs such as torn inlet boots, missing or broken vacuum tees, and/or cracked, broken, or disconnected wire harnesses. Make sure all harness connectors are properly placed and secure in the connectors and holders. This will prevent potential open or short-circuit issues. Also, check connectors for corrosion, frayed wiring, and damaged terminals. In addition, inspect the battery terminals, and check the state of charge before attempting to diagnose possible electrical faults.

Inspect the fuel injector wire(s) and ensure they are connected securely to the fuel injector(s). The engine will have low power at higher engine speeds if the fuel filter is restricted and/or fuel pump operation is degraded. This fault may be caused by one or more disconnected fuel injectors Refer to the Vehicle Emission Warranty Manual for time and mileage coverage for the emission-related fault(s). For additional information, refer to the Service Manual or applicable Technical Service Bulletin (TSB) prior to continuing.

Diagnostic Procedures

a. Turn the ignition ON. Use a Scan Tool to access the Active Test/Fuel Pump Enable to activate the fuel pump. Check for operating noise when the pump is activated and running.

b. Turn the ON, and use a Scan Tool to access and perform the Active Test/Fuel Pump Enable/ON. Access the Live Data when performing the Active Test and observe the Fuel Pressure Sensor parameter. The value should be 46–84 PSI (320–580 kPa).

c. Use a Scan Tool to access and perform the Active Test/Fuel Pump Enable/OFF. Access the Live Data when performing the Active Test and observe the Fuel Pressure Sensor parameter. The value should have decreased to 68–79 PSI (468–544 kPa).

Replace Fuel Pump

Removal

Step 1 - Use a lift or jack to raise the vehicle if necessary.

Step 2 - Remove the fuel tank.

Step 3 - Disconnect the fuel and Evaporative Emission (EVAP) lines from the fuel tank module.

Step 4 - Disconnect the harness connector from the fuel pump module.

Step 5 - Remove the lock ring.

Step 6 - Lift the fuel pump module from the fuel tank.

Step 7 - Remove the fuel pump module.

Installation

Installation is accomplished in the reverse order of removal. During installation, replace worn, cracked, or damaged components (such as the O-ring, spacer, seal, etc.) with new parts.

Repair Validation

1. Erase DTC(s) and Freeze Frame (FF) data.

2. Perform the Key ON Engine OFF (KOEO) and Key ON Engine RUNNING (KOER) test, or perform the drive cycle requirements for the fault area.

3. Optionally, operate the vehicle within the conditions recorded in the Freeze Frame data when DTC P0171 was initially set.

4. Check for pending or confirmed DTCs. If none are found, the repair is complete.