LEMON Manuals: Even more car manuals for everyone
Home >> Ford >> 2000 >> Contour SE, 2.0 3, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 751 (Engine Controls - Diagnostic Methods - CNG, Flex-Fuel & Gasoline) >> Adaptive Fuel DTCs Diagnostic Techniques >> P0171/P0174 System Too Lean Diagnostic Aids >> Exhaust System Leaks:

Exhaust System Leaks:

WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

In this type of condition, the engine may actually be running rich of stoichiometry (14.7:1 air / fuel ratio) because the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. This condition is caused by oxygen (air) entering the exhaust system from an external source. The HO2S will react to this exhaust leak by increasing fuel delivery. This condition will cause the exhaust gas mixture from the cylinder to be rich.

Examples: Exhaust system leaks upstream or near HO2S, poorly welded/leaking HO2S boss, malfunctioning Secondary Air Injection system, etc.

scientia non olet · About LEMON Manuals