# P0174: System Too Lean (Bank 2)

**Verdict:** Drive to a shop this week

Fuel and air metering - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996.

- **Typical cost:** $15-$1,300
- **Urgency:** This week
- **Most likely:** Vacuum leak or dirty MAF sensor
- **DIY?:** Steps 1-3

## Quick answer

P0174 means bank 2 of a V6 or V8 engine is running too lean, with too much air or too little fuel, and the computer cannot add enough fuel to fix it. It often appears with P0171. When both are set, the cause is usually shared, like a vacuum leak or dirty MAF sensor.

## What does P0174 mean?

V6 and V8 engines, along with flat engines like those from Subaru and Porsche, have two rows of cylinders called banks, and each has its own upstream oxygen sensor and its own fuel trims. That lets the engine computer correct each side separately. When the bank 2 sensor keeps seeing extra oxygen, the computer adds fuel to that side through positive fuel trims, both a quick short-term correction and a learned long-term value.

P0174 sets when bank 2 trims reach the computer's positive limit and stay there, meaning that side is getting too much air or too little fuel. Bank 2 is the side without cylinder 1, and which physical side that is depends on the engine. The test runs whenever the engine is warm, and the light usually comes on after two trips. Seeing P0171 at the same time points toward a shared cause rather than a problem on one side.

## What are the symptoms of P0174?

- Check engine light on
- Rough idle
- Hesitation when accelerating
- Possible misfires on bank 2 cylinders
- Poor fuel economy

## What causes P0174?

Ranked from most to least likely. Check them in this order: the cheap, common causes first.

1. **Vacuum leak** (most common). Air leaking in after the MAF sensor is the most frequent reason for lean trims. On V engines, leaks at the intake manifold gaskets, PCV hose or brake booster hose are typical, and many hide under the intake. A leak near the bank 2 runners can set P0174 alone; a central leak usually sets P0171 too.
2. **Dirty MAF sensor** (common). A dirty or failing MAF sensor under-reports airflow for the whole engine, so both banks get too little fuel and P0171 usually sets alongside P0174. It is common after using an over-oiled aftermarket air filter or with a leaking air box seal. Trims that climb with engine speed point to the MAF more than to a vacuum leak.
3. **Low fuel pressure** (less common). A weak fuel pump, clogged filter or faulty regulator starves both banks, and the effect is usually worst under load, such as accelerating or climbing a hill. High-mileage vehicles and those often run on a nearly empty tank are more at risk. A fuel pressure and volume test confirms whether delivery is keeping up.
4. **Clogged injectors on bank 2** (less common). If only bank 2 is lean while bank 1 trims look normal, dirty or partly clogged injectors on that side are a strong suspect. Deposits build up over time, especially in engines that sit unused for long periods. A misfire on one bank 2 cylinder can point to a specific injector, and a shop can flow-test them.
5. **Exhaust leak ahead of the bank 2 upstream oxygen sensor** (less common). A cracked exhaust manifold, broken stud or leaking gasket on bank 2 lets outside air in ahead of that bank's upstream oxygen sensor, making only that bank look lean. Manifold cracks and stud failures are common on some V engines and in road-salt states. A ticking sound from one side on cold start is a clue.

## How do you diagnose P0174?

1. Find out which side of your engine is bank 2 (the side without cylinder 1).
2. Compare bank 1 and bank 2 fuel trims; if only bank 2 is high, look for a leak or injector problem on that side.
3. Inspect vacuum hoses and the PCV system, then have the intake smoke-tested.
4. Clean the MAF sensor if both banks are lean.
5. Test fuel pressure under load if trims rise during acceleration.

## How do you fix P0174, and what does it cost?

| Fix | Typical cost | What it involves |
| --- | --- | --- |
| Clean the MAF sensor | $15-$100 | First step when both banks are lean. |
| Repair a vacuum leak or intake gasket | $100-$900 | Intake manifold gaskets on V engines take more labor. |
| Repair bank 2 exhaust leak | $150-$600 | Manifold gasket or cracked manifold on bank 2. |

Full price breakdowns: [mass air flow sensor replacement cost](/cost/mass-air-flow-sensor-replacement).

## Is it safe to drive with P0174?

> **Drive to a shop this week.** Usually OK for short drives, but a lean engine can misfire and overheat the catalytic converter. Get it fixed within a week or two.

## Will P0174 fail an emissions test?

P0174 keeps the check engine light on, so the car fails an OBD-II emissions test in most states. Lean running can also cause misfires that raise hydrocarbon emissions. After the repair, clear the code and drive several days of mixed trips so bank 2 fuel trims relearn and the readiness monitors complete before you go for the test.

## After the repair: clearing P0174

After the repair, clear the code or reset trims, then compare bank 1 and bank 2 total fuel trims at warm idle and at about 2,500 RPM. Both should sit near zero and close to each other. Drive several mixed trips, including highway, and recheck for pending codes. Matching, stable trims on both banks mean the repair worked.

## How to prevent P0174

- Check intake and PCV hoses on V engines, where leaks often hide under other parts.
- Clean the MAF sensor when you notice rough idle, hesitation or falling mileage.
- Replace the fuel filter on schedule if your vehicle has a serviceable one.
- Use the fuel grade your manual lists; detergent gasoline helps limit injector deposits.
- Fix bank 2 exhaust manifold leaks before they pull in air and fool its sensor.

## Codes often seen with P0174

- [P0171](/codes/p0171): System Too Lean (Bank 1)
- [P0175](/codes/p0175): System Too Rich (Bank 2)
- [P0101](/codes/p0101): Mass or Volume Air Flow "A" Circuit Range/Performance
- [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected

## Frequently asked questions

### What side is bank 2?

Bank 2 is the side of a V6, V8 or flat engine that does not have cylinder 1. Which physical side that is, left or right, front or rear, varies by make and engine, so check a repair manual or service information for your engine before testing parts on that side.

### Can a four-cylinder engine set P0174?

Normally no. Most inline four-cylinder engines have only one bank, so they set P0171 instead. P0174 appears on V6, V8 and flat engines, plus a few inline six-cylinder engines that use two upstream oxygen sensors and treat each half of the engine as a separate bank.

### Why is only bank 2 lean?

When only bank 2 is lean, the cause is usually on that side of the engine. Think of a vacuum leak near the bank 2 intake runners, an exhaust leak before its oxygen sensor or clogged injectors on that bank. A shared problem like a dirty MAF sensor normally makes both banks lean.

### Can I drive with P0174?

Usually yes, for short drives, but do not leave it for long. A lean engine can misfire and overheat the catalytic converter on that bank, and very lean running under load can damage pistons. Get it diagnosed within a week or two, and avoid towing or full-throttle acceleration until then.

### How much does it cost to fix P0174?

Most P0174 repairs cost $15-$1,300. Cleaning the MAF is $15-$100, a vacuum leak or intake gasket repair runs $100-$900 because V-engine intakes take more labor, and a bank 2 exhaust leak costs $150-$600. Fuel delivery repairs sit at the upper end. A smoke test helps target the right repair.

### What causes P0171 and P0174 together?

When both banks are lean, the cause is usually something they share. The most common shared causes are a vacuum leak in the central intake, a dirty or failing MAF sensor and low fuel pressure. Problems on only one side, like a single injector or an exhaust leak, rarely make both banks lean.

### Can I fix P0174 myself?

Some steps, yes. Reading both banks' fuel trims, cleaning the MAF sensor and inspecting hoses are easy at home. Leaks under a V-engine intake manifold are hard to see and usually need a smoke test, and replacing intake gaskets or a bank 2 exhaust manifold is a bigger job most owners leave to a shop.

### Can a bad bank 2 oxygen sensor cause P0174?

Rarely. The bank 2 upstream oxygen sensor usually reports lean correctly because that bank really is lean. If its readings look odd, check first for an exhaust leak ahead of it. Replace it only after leaks, the MAF sensor and fuel pressure check good and the sensor fails a response test.

### How do I find a vacuum leak?

Start by listening for hissing with the engine idling and inspecting hoses for cracks. Watching fuel trims while gently spraying water near suspected spots is a rough home method, but it is not precise. A shop smoke test fills the intake with visible smoke and is the most reliable way to find hidden leaks.

### Can P0174 cause misfires on bank 2?

Yes. A lean mixture is harder to ignite, so P0174 can bring misfire codes for bank 2 cylinders, especially at idle. Fixing the lean condition usually ends the misfires. If one bank 2 cylinder keeps misfiring after the trims are normal, check its spark plug, ignition coil and injector.

## Sources

- [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/)

## Other fuel and air metering codes

- [P0153 O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0153)
- [P0155 O2 Sensor Heater Circuit (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0155)
- [P0156 O2 Sensor Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0156)
- [P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0157)
- [P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0158)
- [P0161 O2 Sensor Heater Circuit (Bank 2 Sensor 2)](https://diagxcar.com/codes/p0161)
- [P0171 System Too Lean (Bank 1)](https://diagxcar.com/codes/p0171)
- [P0172 System Too Rich (Bank 1)](https://diagxcar.com/codes/p0172)
- [P0175 System Too Rich (Bank 2)](https://diagxcar.com/codes/p0175)
- [P0191 Fuel Rail Pressure Sensor "A" Circuit Range/Performance](https://diagxcar.com/codes/p0191)
- [P0087 Fuel Rail/System Pressure - Too Low](https://diagxcar.com/codes/p0087)
- [P0101 Mass or Volume Air Flow "A" Circuit Range/Performance](https://diagxcar.com/codes/p0101)
- [P0102 Mass or Volume Air Flow "A" Circuit Low](https://diagxcar.com/codes/p0102)
- [P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)](https://diagxcar.com/codes/p0151)

## Symptoms

- [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle)
- [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating)
- [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating)
- [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating)
- [Why does my car shake at idle?](https://diagxcar.com/symptoms/car-shakes-at-idle)

## Repair costs

- [Mass air flow sensor replacement cost](https://diagxcar.com/cost/mass-air-flow-sensor-replacement): $150-$450
- [Exhaust manifold gasket replacement cost](https://diagxcar.com/cost/exhaust-manifold-gasket-replacement)
- [Fuel pump replacement cost](https://diagxcar.com/cost/fuel-pump-replacement)

## Warning lights linked to this

- [Check engine light](https://diagxcar.com/warning-lights/check-engine)

## Terms explained

- [What is Fuel trim?](https://diagxcar.com/glossary/fuel-trim)

---

Source page: https://diagxcar.com/codes/p0174
Updated: 2026-11-03
General information, not a substitute for a qualified mechanic.