1997 Dodge Avenger 2.5L V6 P0171 and P0174 OBD2 Codes: Diagnosis & Solutions for Lean Mixtures

To better assist you, could you share your current fuel pressure reading, live fuel trim values (short-term and long-term), the brand of O2 sensors installed, and how the vehicle performs under real-world driving? A true diagnostic scan tool is essential — code readers only capture freeze frame data and don’t show live parameters. Please provide these details so we can narrow down potential causes.

I’m not familiar with how to test fuel pressure or read fuel trims. How do I perform those checks? What brand of O2 sensors should I use for a 1997 Dodge Avenger? Are there known issues with certain brands (like Bosch) causing P0171/P0174 codes even when new? Does the car run well overall, or are there noticeable performance drops?

Let’s clarify: P0171 and P0174 indicate that both engine banks are running too lean — meaning the air-fuel mixture is too rich in air relative to fuel. This isn’t isolated to one bank, so look for systemic issues like vacuum leaks, incorrect fuel pressure, or faulty sensors. I’ve seen Bosch O2 sensors on many 1997 Dodge models trigger these codes even when new — possibly due to sensor calibration mismatch. Consider returning them and replacing with OEM or properly matched aftermarket sensors. If you don’t have the tools or experience for advanced diagnostics, a qualified mechanic should perform fuel trim analysis, fuel pressure testing, and live data monitoring to identify root causes.

What brand of O2 sensors should I buy? AutoZone and Checker only carry generic brands. Is it worth tearing apart the engine (worst-case scenario) or is there a cheaper, more targeted fix given my limited budget?

Avoid purchasing from stores like AutoZone or Checker — they sell the same generic sensors regardless of model. Take your vehicle’s VIN to a Dodge dealership and request OEM upstream O2 sensors. Alternatively, have them scan the system and review fuel trims, fuel pressure, and live data. This approach saves money by avoiding guesswork. A $100 diagnostic check and targeted parts are far more cost-effective than spending $400 on parts with no clear diagnosis.

Can I retrieve fuel trim values using a standard OBD2 scanner?

Only a true scan tool capable of live data monitoring will show real-time fuel trims. A basic code reader saves freeze frame data only and cannot display dynamic parameters like short-term or long-term fuel trims. You need to check fuel trim at idle, 2500 RPM in park, and during steady highway cruising — these are key indicators for diagnosing lean conditions.

New symptom: the engine suddenly cuts out while driving.

Fuel pressure should be checked immediately — a low reading could explain the lean condition and cause intermittent stalling.

The engine died unexpectedly. I’m now at a mechanic. Sorry I didn’t address this sooner.

No need to apologize — please share what the mechanic found so others can learn from your experience and avoid similar mistakes.

I will update with the diagnostic results as soon as possible.

Here’s what I found: fuel trim is at +24.2%. The car runs better now, but the original P0171/P0174 codes persist. After a week of testing, my mechanic suspects an issue with the distributor — it's not firing correctly. He replaced it, and the engine now runs smoothly. However, the same OBD2 codes still appear. The mechanic says the scanner showed a list of potential issues that could trigger these codes; he tested most of them but remains uncertain whether it’s a faulty PCM or something else. He advised resetting the system, but I’m skeptical — any thoughts on this?

Your mechanic may be overlooking key details. Is the fuel trim reading +24 or -24? P0171/P0174 typically point to a positive trim (lean condition), so it’s likely +24. Is this short-term or long-term? What fixed the stalling — was the fuel pump replaced? What is your current fuel pressure? Are you still using Bosch O2 sensors? Where did you purchase the fuel pump?