Symptoms

- Engine Light ON (or Service Engine Soon Warning Light) - Excessive Fuel Consumption

Possible Causes

- Intake air leaks - Faulty front heated oxygen (O2) sensor - Faulty Mass Air Flow (MAF) sensor

When Detected

- Fuel injection system does not operate properly. - The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)

Tech Notes

The P0171 is a very common code for the 2001 Ford Windstar. Here a link to a web site with information how to repair: 1999-2003 Fords Windstar Code P0171

Description

The Powertrain Control Module (PCM) monitors the engine Air/Fuel mixture ratio, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The PCM calculates the necessary compensation to correct the offset between the actual and the theoretical ratios. In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the PCM judges the condition as the fuel injection system malfunction and light up the engine light.