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P0171 OBD2 Fault in 2006 Pontiac Montana SV6 (3.5L V6) - Causes and Diagnostics

Model: 2006 Pontiac Montana SV6 Fault Code: P0171 Posted: 2013-03-02 14:31

My 2006 Pontiac Montana SV6 with a 3.5L V6 engine has recently started triggering the P0171 diagnostic trouble code — System Too Lean Bank 1. Notably, this occurred without any noticeable changes in engine performance or loss of power. The check engine light would stay on for one to two days before turning off intermittently. I previously tried switching to premium gasoline, which resolved the issue during winter months when temperatures dropped below freezing. However, after reverting to regular gas a few days ago, the P017-than code reappeared today. I suspect either a clogged fuel injector or a faulty oxygen sensor, as these components may function properly in cold weather but fail under warmer conditions. I've already attempted MAF (Mass Air Flow) sensor cleaning, but it did not resolve the issue. What are your thoughts on diagnosing and fixing this P0171 code? Any recommended steps or tools? Thanks for your input.

Related fault codes
P0171
Comments (4)
Anonymous 2013-03-02 16:15

Use the manufacturer-recommended fuel type — premium gasoline is only necessary for high-performance vehicles, not standard models. Avoid unnecessary spending on 'premium' fuel. Try an injector cleaner such as SeaFoam, available at most hardware stores like Walmart. Check for vacuum leaks, especially on Bank 1 — a common cause of lean conditions. A simple spray test can help identify leaks quickly. Not everyone has specialized tools, so start with these basic steps. Use an OBD2 scanner to monitor the oxygen sensor B1S1 voltage readings and check freeze frame data and Long-Term Fuel Trim (LTFT) values. Also inspect the Engine Coolant Temperature (ECT) sensor for accuracy.

Anonymous 2013-03-07 21:45

Vacuum leak is a likely cause of this P0171 code, especially in Bank 1.

Anonymous 2013-03-09 00:34

If the engine has only one upstream oxygen sensor (common on older V6 models), vacuum leak remains a plausible explanation. However, if it uses two upstream sensors, the likelihood of a vacuum leak affecting just one bank is reduced.

Anonymous 2013-03-09 09:04

I retired in 2006, so I can't confirm specifics about the 3.5L engine from that year. However, based on my memory, vehicles with 3.4L and 3.5L engines prior to 2002 typically had only a single upstream oxygen sensor.