← Back to list

2007 Ford Taurus V6 3.0L P0174 (Bank 2) System Too Lean After Ignition Coil Replacement

Model: 2007 Ford Taurus Fault Code: P0174 Posted: 2017-04-21 19:06

My 2007 Ford Taurus SEL with a 3.0L V6 engine recently experienced a sudden loss of power while driving, causing the vehicle to stall completely at idle in park. I took it to a mechanic who diagnosed a misfire in cylinder No. 3 and replaced the faulty ignition coil. The issue appeared resolved initially, but just one day later, the Check Engine light returned and now displays OBDII code P0174 (Bank 2) — System Too Lean. So far, the only noticeable symptom has been a single instance of stalling at idle. My question is: could replacing the ignition coil have caused this lean condition? If not, why did it reappear so quickly after the repair? I'm hesitant to return to a mechanic for further diagnosis due to high labor costs and would prefer to troubleshoot and fix this myself if possible. I am experienced in basic engine repairs and would like to understand the root cause of P0174 and how to address it without professional intervention. Any guidance on diagnosing vacuum leaks, fuel delivery issues, or sensor malfunctions would be greatly appreciated.

Related fault codes
P0174
Comments (3)
Anonymous 2017-04-21 22:33

P0174 on Bank 2 typically indicates a lean air-fuel mixture, which can stem from an air leak, insufficient fuel pressure, or a sensor stuck in a lean state. A diagnostic scan tool is essential to identify the exact cause. Did you have any prior error codes that led to replacing the ignition coil? Are there any other active codes besides P0174? It's possible the mechanic inadvertently dislodged a vacuum hose during the repair — especially if one wasn't already present. For DIY troubleshooting, start by testing for vacuum leaks using soapy water or a smoke machine. Also clean the Mass Air Flow (MAF) sensor and verify fuel pressure is within specifications.

Anonymous 2017-08-02 09:04

I own a 1998 Mercury Sable with a similar issue. It began with a flashing check engine light and P0305 (cylinder 5 misfire). After replacing plugs, wires, and the ignition coil, the P0305 cleared but P0174 appeared. Since then, I've replaced the MAF sensor, air filter, PVC valve, manifold gaskets, and fuel injector in cylinder 5. Despite extensive work, we still can't find a vacuum leak. Our current theory is a faulty oxygen (O2) sensor causing false lean readings. If anyone has successfully resolved this issue on their vehicle or knows of a reliable O2 sensor test method for Bank 2, I’d appreciate the insight.

Anonymous 2017-08-02 18:06

To determine whether the cause is a vacuum leak or fuel delivery issue, monitor the fuel trims at idle versus under load. If the fuel trim shows high positive values that drop when engine load increases, this points to a vacuum leak. If the trim remains consistently high or rises specifically on Bank 2 during operation, it suggests a fuel-related problem in that bank. Test the pre-catalyst O2 sensor response by quickly snapping the throttle — the reading should spike and then return to normal. If it doesn’t respond properly, this may indicate a faulty sensor. Could you share your idle and 2500–3000 RPM fuel trim readings? This data would help pinpoint whether the issue is mechanical or sensor-based.