P0171 Diagnostics (1996-2010 3.3L V6 Chrysler, Dodge, And Plymouth Minivan)

One of the most common diagnostic trouble codes your 3.3L V6 Chrysler, Dodge, or Plymouth minivan is gonna throw at you is the P0171: System Too Lean Bank 1.

DTC P0171 can be a real head scratcher, since quite a few things can cause it, but at the heart of the issue, the engine is running too "lean" —too much air and not enough fuel in the air/fuel mixture the engine is burning.

In this tutorial, I'll walk you through what this DTC means in plain English, the most common causes, and show you how this code is diagnosed with several tests to find out the exact cause of it.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.3L V6 Chrysler Town & Country: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 3.3L V6 Chrysler Voyager: 2000, 2001, 2002, 2003.
• 3.3L V6 Dodge Caravan: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.3L V6 Dodge Grand Caravan: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 3.3L V6 Plymouth Voyager: 1996, 1997, 1998, 1999, 2000.
• 3.3L V6 Plymouth Grand Voyager: 1996, 1997, 1998, 1999, 2000.

What DTC P0171 Means

P0171 means your minivan's PCM (Powertrain Control Module) has detected that the engine is running too lean.

"Too lean" means there's too much air and not enough fuel in the air/fuel mixture being burned (combusted) in the cylinders.

This lean condition is usually caused by something outside the PCM's control —like an intake manifold gasket leak (just one example; there are other possible causes too)— and the PCM starts to panic.

To compensate, the PCM begins adding more fuel than normal, which shows up as elevated long-term fuel trims —typically over +15%.

Although the PCM is trying to correct the issue by adjusting fuel delivery, it's not a perfect solution. You'll still run into drivability problems as the system struggles to maintain the ideal air/fuel ratio for smooth and efficient engine operation.

P0171: Why Both Banks Are Actually Affected

The P0171 trouble code is officially defined as “System Too Lean –Bank 1”. That wording makes it sound like only Bank 1 —the cylinder bank on the firewall side (cylinders 1, 3, and 5)— is affected by the lean condition. But on the 1996–2007 3.3L V6 Chrysler, Dodge, and Plymouth minivans, that's not actually the case.

These engines are equipped with only one upstream oxygen sensor, and it's located in a position where it samples exhaust gases from both cylinder banks.

That means the PCM isn't reading Bank 1 and Bank 2 separately —it sees a blended exhaust stream and makes fuel adjustments for all six cylinders based on that single O2 sensor's feedback.

So even though the code says “Bank 1,” the underlying issue is affecting the entire engine.

Whether it's a vacuum leak, low fuel pressure, or a faulty sensor, the cause of the lean condition is impacting combustion across all six cylinders —not just one side of the engine.

This is a critical detail to understand when diagnosing a P0171 on your minivan, because chasing a problem isolated to Bank 1 will lead you in the wrong direction. Always approach this code as a full-engine lean condition.

Common Causes Of DTC P0171

Quite a few things can cause trouble code P0171, that it can be a real challenge to pinpoint the root cause of the problem.

In the list below, I'm listing some of the most common causes of P0171.

1. Vacuum leaks: Cracked vacuum hoses/lines, a failed lower intake manifold gasket, or PCV connections allowing unmetered air into the system.
   • The lower intake manifold gasket —commonly called the "valley pan" gasket— is a well-known failure point. It's a thin steel shim gasket with just enough sealant to barely hold a seal between the intake ports and the cylinder heads.
   • This thin steel shim gasket design practically guarantees you an eventual intake manifold vacuum leak issue (and a steady donation to the repair economy).
   • One of the earliest warning signs, even before a vacuum leak sets off the P0171 code, is engine coolant seeping from the corners of the lower intake manifold —usually on the passenger side.
   • If you're spotting coolant leaks from one or more corners of the lower intake manifold, chances are high you've just found the root cause of the P0171.
2. Low fuel pressure: If the fuel pump is failing and starving the engine of fuel, it's gonna trigger a P0171 DTC.
   • These minivans have a fuel pressure spec (around ~55–60 PSI, check service data) and if pressure is below spec under load, the engine is gonna run lean.
3. Exhaust leaks: A leak in the exhaust manifold or pipe ahead of the upstream O₂ sensor can let outside air enter the exhaust stream, fooling the sensor into seeing a lean condition.
   • The front O2 sensor is designed to report the oxygen content of the exhaust gases exiting the engine.
   • If a leak allows ambient air —which is rich in oxygen— to mix with the exhaust before it reaches the sensor, it throws off the reading.
   • This causes the O2 sensor to falsely report a lean condition, prompting the PCM to add more fuel than necessary.
   • The PCM then adjusts the fuel trim to compensate and flags a code P0171 if it hits its limit.
4. Clogged or dirty fuel injectors: Not delivering enough fuel to match the airflow entering the engine.
   • Often, fuel injector issues will also trigger misfire codes if cylinders are getting inadequate fuel.
5. Bad upstream O2 sensor (less common): In most cases P0171 by itself is not due to a bad O₂ sensor.
   • The PCM will typically set a specific O₂ sensor code if the sensor performance is bad.
   • In fact, the absence of an O₂ sensor circuit code alongside P0171 usually indicates the sensor is functioning and detecting a genuine lean condition.

Start By Checking Short Term Fuel Trim (STFT)

The one thing that'll save you a ton of time and frustration when troubleshooting a P0171 is hooking up a generic scan tool with live data and checking whether a continuous lean condition is actually present.

You can confirm this quickly and easily using any basic scan tool that supports live data. In the scan tool's "live data" section, look for the parameter ID (PID) labeled short-term fuel trim 1 (ST FTRM 1).

• NOTE: Each scan tool uses its own abbreviation for Short Term Fuel Trim 1. Consult your scan tool's user manual or live data legend to see how it's labeled.

Make sure the engine is fully warmed up, idling, and the PCM is in closed loop mode during this check.

Under normal operating conditions —when there's no lean condition— the short-term fuel trim 1 (STFT 1) should hover around 0%, usually fluctuating within a ±5% range as the PCM makes minor real-time adjustments.

• A positive (+) value means the PCM is adding fuel to correct a lean condition.
• A negative (–) value means the PCM is pulling fuel to correct a rich condition.

Keep in mind, it's completely normal for the PCM to constantly adjust STFT 1 while in closed loop operation.

But if the engine is running with a continuous lean condition, you'll notice that STFT 1 (and usually long-term fuel trim, LTFT 1) stays significantly positive —often around +20% or more. That's a clear sign the PCM is trying hard to compensate for a lack of fuel or excess air.

In most P0171 cases, LTFT on Bank 1 will be pegged in the +20 to +30% range, especially at idle, and STFT will also be elevated. This indicates the lean condition isn't just a brief glitch —it's a persistent problem.

Once you've confirmed that your minivan has a persistent lean condition by checking the STFT 1 values, it's time to roll up your sleeves and start running specific tests to track down its exact cause.

For a bit more info on the subject, see these sections:

• What Is A Fuel Trim?
• What Does Rich and Lean Mean?

What Tests Are Needed To Diagnose Trouble Code P0171 (System Too Lean)

To get to the bottom of a P0171 on your 1996–2007 3.3L V6 Chrysler, Dodge, or Plymouth minivan, you'll need to run a few key diagnostic tests.

Each one helps rule out a specific cause —whether it's unmetered air sneaking into the intake or not enough fuel reaching the cylinders.

More specifically, tracking down the root of a P0171 is all about process of elimination —and to do that, you need a solid test strategy. That's exactly what I'll walk you through in this section.

OK, once you've confirmed that the engine is operating with a continuous lean condition, below is a list of the tests you'll need to run, with links to detailed tutorials that'll walk you through each one step by step.

Easy: Start with these simple, quick to perform, and non-invasive tests.

• Upstream O2 Sensor Check: If the upstream oxygen sensor is faulty —stuck or slow to respond— it can send incorrect lean signals to the PCM.
  • This throws off fuel trims and leads to a false P0171 code.
  • What you want to do is check it for accuracy and response time.
  • Since it's a super easy test to do, I recommend starting here.
• Exhaust Leak Inspection (upstream of O2 sensor): An exhaust leak ahead of the upstream O2 sensor can allow outside air to enter the exhaust stream.
  • Key areas you'll need to inspect include the exhaust manifold gaskets, cracked exhaust manifolds, and the pipe connecting the front manifold to the rear one —basically, any spot that could leak exhaust gas before it reaches the upstream oxygen sensor.
  • It's a simple check you can do without any special tools, and it's best to get it out of the way early in the diagnostic process.
• MAP Sensor Check: A MAP sensor filled with engine oil (internally) can cause the PCM to miscalculate engine load or airflow.
  • This sensor uses a large-diameter vacuum port that inserts directly into the intake manifold plenum —unlike some MAP sensors that rely on a long vacuum hose to supply intake vacuum.
  • On high-mileage engines or engines burning oil, it's not uncommon for blow-by gases to cause oil to accumulate in the plenum, eventually soaking the MAP sensor.
  • This contamination leads to inaccurate pressure readings, which throws off fuel calculations and can result in a lean condition.
  • This type of issue usually won't set a MAP sensor DTC.
  • So if the basics have checked out, remove the sensor from the intake manifold and inspect it. If it's filled with oil or has carbon buildup blocking the vacuum port, clean it thoroughly.
  • Reinstall the sensor, clear any stored codes, and take the vehicle for a road test to see if the lean condition clears and the fuel trims return to normal.

More Involved: These tests require more time, tools, or access —save them for after you've ruled out the basics.

• Vacuum Leak Test (Carb Cleaner Method): A major vacuum leak —whether from a cracked vacuum hose, PCV line, or leaking intake manifold gasket— is one of the most common causes of a P0171 DTC. That's why this is the first test you should run.
  • Spraying carb cleaner around suspected leak points is a quick and effective way to detect unmetered air entering the intake manifold. Starting fluid or even brake cleaner will work too.
  • If engine idle changes when you spray a specific area, you've found the source of the vacuum leak.
  • This tutorial explains how to safely perform this test: How To Check For Vacuum Leaks Using Carb Cleaner Spray (1989-2003 5.2L, 5.9L V8 Dodge Ram Pickup).
• Fuel Pressure Test: Once you've ruled out a major vacuum leak as the cause of the P0171, the next step is to check fuel pressure.
  • A fuel pressure test with a fuel pressure test gauge will help you determine whether the fuel pump, filter, or pressure regulator is doing its job —or if one of them is falling short and starving the engine of fuel.
  • Only the 1996-2003 minivans have a replaceable fuel filter mounted outside the gas tank (it's locate above the gas tank).
  • Fuel pressure regulator is part of the fuel pump module assembly in the gas tank.
• Injector Spray Test: Weak, dirty, or partially clogged fuel injectors can reduce fuel delivery and cause a lean condition in individual cylinders.
  • This isn't a common cause of a P0171, but it's still a possibility in certain cases.
  • Diagnosing clogged injectors isn't for the faint of heart —it involves identifying the problem injector(s), removing them, hooking them up to a fuel injector cleaner/test kit, and inspecting the spray pattern.
  • This should be one of the last tests you run —only after ruling out all the more common causes of a P0171 DTC.
  • In most cases, one of the earlier tests will point you to the real issue —about 90% of the time, this step isn't needed.

What Is A Fuel Trim?

Fuel trims are the PCM's way of fine-tuning the air-fuel mix to keep the engine running smooth. Every time you fire up the engine, the PCM is constantly watching sensor data and adjusting how much fuel gets injected —second by second.

There are two types of fuel trim you'll see on the scan tool (specific to the 1996-2009 minivans I'm covering in this tutorial):

• Short-Term Fuel Trim 1 (STFT 1):
  • These are quick, real-time adjustments.
  • The PCM uses input from the upstream oxygen sensor to tweak the fuel delivery up or down as the engine runs.
  • It's like a moment-to-moment correction —one second it's adding a little fuel (positive value), the next it's taking some out (negative value), depending on what the O2 sensor is reporting.
• Long-Term Fuel Trim 1 (LTFT 1):
  • These are more permanent adjustments based on what's been happening over time.
  • If the PCM sees that it's constantly having to add fuel in the short term, it "learns" from that and starts adjusting the long-term trim.
  • High LTFT (usually over +10 to +15%) means the PCM is compensating for a problem —like extra air sneaking in or not enough fuel being delivered.

When diagnosing a lean condition like P0171, the long-term fuel trim is your smoking gun. If it's high and STFT is also consistently adding fuel, you've got a real problem —not just a temporary blip. And now it's time to find out what's causing it.

NOTE: The way fuel trims are labeled can vary between different scan tools and software. For example:

• STFT 1 and LTFT 1 could be also labeled as STFT B1 and LTFT B1.

It's essential to consult your scan tool's documentation to understand its specific labeling conventions.

What Does Rich And Lean Mean?

When we say an engine is running "rich" or "lean", we're talking about the balance of air and fuel going into the cylinders.

That balance is critical —the engine needs the right mix to make clean power and keep everything running smooth.

Here's a break down of each term:

• Rich: Too much fuel, not enough air.
  • The engine's burning more gas than it should.
  • You might notice black smoke from the tailpipe, rough idle, or bad gas mileage.
  • A rich condition can foul spark plugs and damage the catalytic converter over time.
• Lean: Too much air, not enough fuel.
  • That's what DTC P0171 is all about.
  • A lean mix makes the engine run hotter, can cause hesitation, misfires, or even stalling.
  • It's also harder on internal engine parts if it goes on too long.

The PCM (Powertrain Control Module) constantly monitors this air-fuel balance using sensors —mainly the upstream oxygen sensor in the exhaust stream. That sensor reports whether the exhaust gases contain more oxygen (lean) or less oxygen (rich), based on what's left over after combustion.

If the sensor sees oxygen levels that are consistently too high, it tells the PCM the engine is running lean. If it sees too little oxygen, it indicates a rich condition. The PCM then adjusts fuel trims to bring the mixture back in line.

But when the lean issue is too severe —like a vacuum leak, weak fuel pressure, or false sensor reading— and the PCM can't correct it with fuel trim alone, it sets a trouble code like P0171.

More 3.3L V6 Chrysler, Dodge, And Plymouth Minivan Tutorials

I've written several more tutorials for the V6 Chrysler, Dodge, and Plymouth minivans that you might find helpful. You can browse them all in this index:

• 3.3L V6 Chrysler, Dodge, And Plymouth Minivan Index Of Articles.