Dirty or faulty mass air flow (MAF) sensor (over-oiled air filters can contaminate it; on some vehicles the MAF leaks its silicone potting material). Vacuum leak after the MAF sensor: intake manifold gaskets, vacuum hoses, PCV hoses. Fuel delivery problem: plugged fuel filter, weak fuel pump, regulator, rail or injectors. Plugged or dirty fuel injectors. PCM software that needs updating (RepairPal). Check for TSBs or a dealer reflash.

Clean or replace the MAF sensor. Repair vacuum, PCV or intake manifold gasket leaks. Restore fuel pressure (filter, pump or regulator). Clean or replace faulty injectors. Update PCM software if a bulletin applies.

P0174⛽ Fuel / air meteringDrive with caution, fix soon

P0174: System Too Lean (Bank 2) (Meaning, Causes, Fixes)

Q: What does P0174 mean?

P0174 means the upstream oxygen sensor on Bank 2 sees too much oxygen in the exhaust, and the engine computer has hit its limit on adding fuel to that bank. A dirty MAF sensor, a vacuum leak, or a fuel delivery problem is the usual cause. The PCM uses the upstream (front) oxygen sensor to keep the air-fuel ratio near 14.7:1, adding or removing fuel as needed. When the Bank 2 sensor still reads lean after the PCM has added as much fuel as it's allowed to, it sets P0174. Bank 2 is the side of a V6/V8/V10/V12 engine that does not have cylinder #1. P0174 is the Bank 2 twin of P0171, and the two often appear together, which points to something both banks share. OBD-Codes.com notes the code can also set when the PCM commands more fuel but the injectors don't actually deliver it.

Q: Can I keep driving with P0174?

Drive with caution, fix soon. Usually drivable short-term, and you may not notice anything. But a lean engine can lose power, knock (detonate), hesitate or misfire, and it pollutes more (oxides of nitrogen). Get it diagnosed soon rather than ignoring it.

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0174 means

The PCM uses the upstream (front) oxygen sensor to keep the air-fuel ratio near 14.7:1, adding or removing fuel as needed. When the Bank 2 sensor still reads lean after the PCM has added as much fuel as it's allowed to, it sets P0174. Bank 2 is the side of a V6/V8/V10/V12 engine that does not have cylinder #1. P0174 is the Bank 2 twin of P0171, and the two often appear together, which points to something both banks share. OBD-Codes.com notes the code can also set when the PCM commands more fuel but the injectors don't actually deliver it.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable short-term, and you may not notice anything. But a lean engine can lose power, knock (detonate), hesitate or misfire, and it pollutes more (oxides of nitrogen). Get it diagnosed soon rather than ignoring it.

Common symptoms

Check engine light on (often the only symptom)
Lack of power or hesitation/surge on acceleration
Increased fuel consumption (OBD-Codes.com)
Spark knock (detonation)
'Coughing' or misfiring, and trouble idling when warm or at a stoplight (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Dirty or faulty mass air flow (MAF) sensor (over-oiled air filters can contaminate it; on some vehicles the MAF leaks its silicone potting material)
Vacuum leak after the MAF sensor: intake manifold gaskets, vacuum hoses, PCV hoses
Fuel delivery problem: plugged fuel filter, weak fuel pump, regulator, rail or injectors
Plugged or dirty fuel injectors
PCM software that needs updating (RepairPal). Check for TSBs or a dealer reflash.

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Clean the MAF sensor with a cleaner that's safe for it. Be careful not to damage it, and let it dry before reinstalling.
Inspect all vacuum and PCV hoses and the intake ducting for cracks or loose connections; replace damaged hoses.
Check the intake manifold gaskets for leaks.
If you have a scanner with live data, compare short- and long-term fuel trims on both banks.
Check for a dirty fuel filter and, with a gauge, proper fuel pressure.
Ask a dealer, or search NHTSA, for technical service bulletins. RepairPal lists outdated PCM software as a common cause.

Typical fixes

Clean or replace the MAF sensor
Repair vacuum, PCV or intake manifold gasket leaks
Restore fuel pressure (filter, pump or regulator)
Clean or replace faulty injectors
Update PCM software if a bulletin applies

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

You can't find the leak: a shop can run a smoke test
Fuel pressure testing needs a gauge and the right adapter
The code returns after the cheap fixes

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Why do I have P0171 and P0174 together?

Both banks are lean, which points to something they share, such as the MAF sensor, a vacuum leak, or low fuel pressure. OBD-Codes.com says this pairing is common on some Fords (e.g. 4.6L and 5.4L V8s).

Is P0174 urgent?

Sources differ. RepairPal rates it 'Urgent'; OBD-Codes.com says you more than likely won't notice drivability problems. Either way, fix it soon: lean running can cause knock and misfires.

Should I replace the Bank 2 oxygen sensor?

Usually not. RepairPal says P0174 is NOT an oxygen sensor problem and lists O2 sensor replacement as the common misdiagnosis: the sensor is accurately reporting a lean mixture. Check the MAF, vacuum leaks and fuel delivery first.

What fixes P0174 most often?

OBD-Codes.com says that in many cases simply cleaning the MAF sensor does the trick.

Sources

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.