U0171 Diagnostic Trouble Code

U0171 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code.

It is considered generic because it applies to all makes and models of vehicles, although specific repair steps may be different depending on your car model.

Symptoms

Symptoms of a U0171 diagnostic trouble code may include:

Faulty or damaged wiring
The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
Poor fuel economy
Rich or lean exhaust

Possible Causes :

Faulty IMRC actuator relay (if equipped)
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.

Repair Processes :

If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for. With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground.

Process Tips

Diagnostic trouble code U0171 is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before U0171.

Fortunately, U0171 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U0171 Trouble Code For Specific Cars

U0171 Ferrari P5 Key Line Voltage
U0171 Holden Vn Pressure Control Solenoid "A" Open Circuit
U0171 Kia Sorento Secondary Air Injection System Switching Valve B Circuit Open
U0171 Hummer H3 Right Tail Lamp Circuit Short to Ground
U0171 Triumph 1800 Passenger's Front Seat Up Switch Circuit Short to Battery
U0171 Saab 9-7 Ignition Tach Circuit Open
U0171 Ginetta G2 Oil Pressure Control Solenoid Circuit Malfunction