P0171 means the engine has reported a lean mixture condition on bank 1. It is not an instruction to buy an oxygen sensor. The VAG reference from Ross-Tech directs attention to airflow measurement, unwanted air and fuel delivery, among other checks.
Record how the fault behaves
Does it appear at idle, during a steady cruise or under acceleration? Does the engine run roughly, or is the warning lamp the only symptom? Those details make a fuel-trim report more useful. Fuel trims describe corrections made by the controller; they need engine speed, temperature and operating conditions beside them.
A garage should distinguish measured results from assumptions. For example, a report saying that a leak test found a particular hose is stronger evidence than a list of likely parts. Likewise, record how fuel delivery was assessed, rather than simply writing that the pump runs.
Keep related symptoms together
Include misfire codes, a recent intake repair, unusual hissing or a change after refuelling. Do not keep driving a badly misfiring vehicle to gather more data. If fuel is leaking or there is a strong unexplained fuel smell, stop using the vehicle and arrange help.
AXION accepts electrical diagnostic enquiries with the scan and previous test results. If controller repair is being proposed, we first need to understand why the findings point beyond the engine’s air and fuel systems.
Arrange an assessment
For ECU testing and repair, send the vehicle details and fault report to AXION. We support enquiries from drivers and garages. Workshop, postal and remote options depend on the job and are confirmed before booking.
Technical reference
Read the supporting technical documentation. The referenced design or vehicle application defines its scope; it is not a universal repair procedure.
Related reading
P0172 rich running needs more than an oxygen-sensor guess. Browse the automotive electronics repair library for other systems and symptoms.