SOURCE: ford f150 2003 po171 always
Code Po171 indicates a lean condition on cylinder bank #1 of the engine. This is the drivers side of the engine. I would suggest replacing both front oxygen sensors as a pair to start. An oxygen sensor has a life span of about 5 years and yours are now 9 years old if they are original. When they get older they are slow to respond to changes in the oxygen content of the exhaust and can trigger a code Po171. If you continue to have the same code set after the replacement of both oxygen sensors then it is time to find out why your engine is running lean. Some of the most common causes are an ignition misfire and a vacuum leak. I have also seen Fords EGR flow sensor (known by Ford as Delta Pressure Feedback sensor) to cause problems like that as well. A good mechanic with a scan tool can usually spot a problem like that in a few minutes.
P1100 Manifold Absolute Pressure Sensor Range/Performance
P1102 Manifold Absolute Pressure Sensor Circuit Low Input
P1103 Manifold Absolute Pressure Sensor Circuit High Input
P1123 Lang Term Fuel Trim Adaptive Too Lean
P1124 Long Term Fuel Trim Adaptive Too Rich
P1127 Long Term Fuel Trim Multiplier Too Rich
P1128 Long Term Fuel Trim Multiplier Too Lean
P1134 HO2S Bank 1 Sensor 1 Transition Time Switch (Bank 1 Sensor I)
P1154 HO2S Bank 2 Sensor 1 Transition Time Switch (Bank 2 Sensor 1)
P1166 HO2S Bank 1 Sensor 1 Controller Adaptive Diagnosis Fault (Bank 1)
P1167 HO2S Bank 1 Sensor 1 Controller Adaptive Diagnosis Fault (Bank 2)
P1168 HO2S Bank 1 Sensor 1 Heater Power Incorrect (Bank 1 Sensor 2)
P1169 HO2S Bank 1 Sensor 1 Heater Power incorrect (Bank 2 Sensor 2)
P1372 Segment Time Incorrect
P1400 Manifold Differential Pressure Sensor Circuit
P1440 EVAP System Vent Solenoid Circuit
P1443 EVAP System Fault (Fuel Tank Cap Missing)
P1510 Idle Control Valve Opening Circuit Shorted (Coil 1)
P1511 Idle Control Valve Command Signal Shorted (Coil 2)
P1513 Idle Air Control Valve Opening Coil Circuit Open (Coil 1)
P1521 Power Steering Switch Input Circuit
P1529 Customer Snapshot Request VIA CAN
P1552 Idle Air Control Valve Closing Coil Circuit Shorted
P1553 Idle Air Control Valve Closing Coil Circuit Open
P1586 Encoding Signal Circuit Not Rationale
P1602 Serial Communication Fault with Transmission Control Unit
P1605 Rough Road Sensor Circuit
P1606 Rough Road Sensor Circuit Not Valid
P1611 MIL Request Signal Circuit Low Input
P1613 ECU Self-Test Failed
P1614 MIL Request Signal Circuit High Input
P1616 Main Relay Fault
P1623 Diagnostic Lamp Power Stage Fault
P1624 MIL On Request Signal//Cooling Fan Relay Low Circuit
P1625 Cooling Fan Relay High Circuit
P1665 Power Stage Group 'A' Fault
P1670 Power Stage Group 'B' Fault
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