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P0171 Fuel Bank 1 Lean Only - 1996 Mercury Cougar 6-Cylinder Diagnosis

Model: 96 mercury cougar Fault Code: P0171 Posted: 2008-07-20 16:55

I own a 1996 Mercury Cougar with a 6-cylinder engine, and my check engine light is currently on. The diagnostic trouble code (DTC) displayed is P0171, indicating a lean condition in Fuel Bank 1. After reviewing similar posts, I notice that many vehicles with this issue also show P0174 (lean condition in Fuel Bank 2) along with an EGR-related code. However, my vehicle only reports P0171 — not the other codes or any EGR fault. The OBD-II monitor status shows that the EGR system is 'complete,' though I'm unsure what this exactly means. I'm now considering inspecting the EGR valve as a potential cause. Here are my freeze frame data readings: - Fuel System 1: CLOSED LOOP - Fuel System 2: NOT SUPPORTED - Calculated Load Value: 90.98% - Engine Coolant Temperature: 206.60°F - Short Term Fuel Trim - Bank 1: +7.81% - Long Term Fuel Trim - Bank 1: +25.00% - Short Term Fuel Trim - Bank 2: +7.03% - Long Term Fuel Trim - Bank 2: +25.00% - Engine RPM: 2125 rpm - Vehicle Speed Sensor: 60.90 mph I'm seeking insight into why only P0171 is present and not the corresponding P0174 or EGR fault codes. Thank you, Robert Strom

Related fault codes
P0171
Comments (3)
Anonymous 2008-07-21 10:45

The freeze frame data suggests Bank 2 may also be leaning, though it's not yet showing a code. Check for vacuum leaks and any sources of unmetered air. Also verify fuel pressure levels. When was the last time you replaced the fuel filter or oxygen sensors? Any updates on these components would help diagnose the issue. Good luck — please share your findings if the code returns.

Anonymous 2008-07-21 15:53

This appears to be a common symptom where both sides of the engine show similar lean conditions, but only one bank triggers a diagnostic code due to system thresholds or sensor sensitivity differences.

Anonymous 2008-07-23 21:05

Thanks for the advice. I've already cleaned the MAF sensor and performed a thorough vacuum leak check. The oxygen sensors and fuel filter have not been replaced since I purchased the car about three years ago. Since there are no noticeable performance issues, I'm choosing to monitor the situation and wait to see if the P0171 code returns in the future. Will update if it reappears.