P0174 Code: System Too Lean (Bank 2)

What does P0174 mean?

P0174 means bank 2 is running lean: there is more air, or less fuel, than the engine computer wants on that side of the engine. Carista describes it as the computer adding significant extra fuel on bank 2, with fuel trims at their limit ^[1].

A V-type engine has two rows of cylinders called banks. Bank 1 is the side that holds cylinder 1, and bank 2 is the other side. Each bank has its own upstream oxygen sensor, so the computer can trim fuel separately for each side. When the bank 2 sensor keeps reporting a lean exhaust even after the computer has added all the fuel it can, P0174 sets and the check engine light comes on. Inline four-cylinder engines have only one bank, so they set P0171 instead.

A lean code tells you the mixture is wrong, not which part is broken. The oxygen sensor is usually reporting a real problem rather than causing one.

Is it safe to drive with P0174?

Usually yes for a short time, but P0174 is a "fix soon" code. Many drivers notice nothing. Others feel hesitation, a hunting or rough idle, weak power under load, or worse fuel economy; Carista notes the symptoms are usually worst at idle and light load ^[1]. If your idle is rough, our rough idle guide covers other causes too.

Do not let it ride for months. A lean mixture burns hotter and can lead to misfires. The California Air Resources Board says most manufacturers advise service as soon as conveniently possible when the light comes on, and that continued driving can damage other parts ^[3].

If the check engine light flashes or the engine shakes, pull over when it is safe and stop driving. CARB explains that a blinking light means a malfunction that could be damaging the catalytic converter. Our page on a flashing check engine light explains what to do next, and misfire codes like P0300 often appear alongside lean codes.

What causes P0174?

The causes match P0171, just on the other bank. Most common first:

1. Vacuum or intake air leak. A cracked intake boot, a torn PCV hose or a leaking intake manifold gasket. Carista calls vacuum leaks the most common cause and recommends a smoke test first. Any air that enters after the MAF sensor is air the computer never measured, so it cannot add the right amount of fuel for it. A leak at the bank 2 end of the intake manifold can make only that side lean.
2. Dirty or faulty MAF sensor. It feeds both banks on most engines, so a sensor that under-reads airflow usually makes both sides lean. Some V engines have two MAF sensors, one per bank, and then a dirty bank 2 sensor can set P0174 alone.
3. Low fuel pressure. A weak pump or clogged filter starves both banks. The lean condition is often worst under load, such as climbing a hill or merging onto a highway, when the engine needs the most fuel.
4. Restricted bank 2 fuel injectors. Deposits can narrow an injector's spray so it delivers less fuel than commanded. One weak injector may also show up as a misfire on that cylinder.
5. Faulty bank 2 oxygen sensor. Check it last, after air and fuel causes are ruled out. An exhaust leak just ahead of the sensor can also pull in outside air and make the exhaust look leaner than it is.

The real trick with P0174 is reading which other codes are set. ALLDATA DIY reminds readers that a code identifies a system rather than a failed part, and that the simplest, least expensive possibility should be checked first ^[2].

Pattern	What it suggests	First check
P0174 only	Something on bank 2 only	Intake gasket and hoses on the bank 2 side, bank 2 trims
P0174 and P0171	Shared air or fuel problem	Intake boot, PCV, MAF sensor, fuel pressure
P0174 and P0172 or P0175 history	Fuel quality or sensor issue	Ask about a manufacturer bulletin, check MAF data
P0174 with misfire codes	Lean misfire on bank 2	Stop if the light flashes; diagnose promptly

How do you diagnose P0174?

Start with information, then cheap checks, then tests that need a shop. Our guide on how to use an OBD2 scanner explains freeze frame and live data.

1. Read all codes and freeze frame. Note rpm, load and coolant temperature when P0174 set. Idle points to a vacuum leak; high load points to fuel delivery.
2. Compare long term fuel trims for both banks. Carista says a large difference between bank 1 and bank 2 points to a bank 2 problem ^[1]. Similar high trims on both banks point to a shared cause.
3. Visual check, engine off. Inspect the intake boot, vacuum lines and PCV hoses, and make sure the oil cap and dipstick seal.
4. Listen at idle for hissing near the bank 2 side of the intake. Keep clear of belts and the fan.
5. Inspect the air filter and MAF sensor.
6. Smoke test and fuel pressure test. A shop smoke test finds hidden intake gasket leaks. Fuel pressure work involves a pressurized system, so have a qualified technician do it.
7. Bank 2 oxygen sensor last.

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

Fix what the diagnosis finds. A loose clamp or a cracked vacuum hose is a small job. A dirty MAF sensor may only need cleaning with MAF-safe cleaner. An intake manifold gasket on a V engine, a fuel pump, or injectors take more labor and cost more.

We have not found a reliable U.S. cost survey for P0174 as of November 2026, so we do not give a dollar range. Cost depends on the failed part, how much has to come apart to reach it (bank 2 parts often sit near the firewall), shop diagnostic time, and whether the repair falls under an emissions warranty or a manufacturer bulletin. For example, Toyota bulletin T-SB-0166-19 lists P0174 among the codes on some flex-fuel 5.7L Tundra and Sequoia trucks and says that repair is covered under the federal emission warranty ^[5]. See our P0171 on Toyota page for details.

After the repair, clear the code and drive normally. Clearing a code does not fix anything, and it resets the readiness monitors that inspection stations check. California requires all monitors to be set to pass Smog Check, and they complete through normal driving or a drive cycle ^[4].