Fuel & air metering · Powertrain · generic (SAE-defined)
P0174: System Too Lean (Bank 2)
P0174 means the engine computer has reached its limit adding fuel on bank 2, the side opposite cylinder 1, because that bank is receiving too much air or too little fuel.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0174 sets
The powertrain control module (PCM) relies on the bank 2 upstream oxygen sensor to keep that bank's air-fuel mixture balanced, and it stores its corrections as short term and long term fuel trims. When bank 2 keeps reading lean, the PCM adds fuel. If the needed correction stays beyond the calibrated limit for long enough, P0174 sets. Because only V-type and flat engines have a bank 2, this code is limited to those designs. Trim limits are manufacturer-specific.
Common causes of P0174
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Vacuum leak, especially at the intake manifold gasket on bank 2
- Dirty or failing mass air flow (MAF) sensor
- Leaking positive crankcase ventilation (PCV) valve, hose or valve cover gasket
- Low fuel pressure from a weak pump, clogged filter or faulty regulator
- Clogged fuel injectors on bank 2
- Exhaust leak ahead of the bank 2 sensor 1 oxygen sensor
- Cracked intake boot or loose intake clamp
P0174 symptoms
- Check engine light on
- Rough idle or idle that hunts up and down
- Hesitation or stumbling on acceleration
- Lean misfire, sometimes with misfire codes
- Hissing noise from a vacuum leak
- Sometimes no noticeable symptoms
How P0174 is diagnosed
- Scan for codes and freeze frame; if P0171 is also present, focus on causes common to both banks, such as the MAF sensor, fuel pressure or a central intake leak.
- If only bank 2 is lean, compare bank 1 and bank 2 fuel trims and look for leaks or injector problems specific to bank 2.
- Smoke test the intake system and inspect vacuum lines, the intake boot, PCV components and intake gaskets.
- Clean the MAF sensor and check its readings against expected values at idle and higher engine speeds.
- Test fuel pressure and volume under load.
- Check for exhaust manifold leaks on bank 2 ahead of the upstream sensor.
- Confirm the bank 2 upstream oxygen sensor responds properly to rich and lean changes.
Typical fixes for P0174
- Repair vacuum or intake gasket leaks
- Clean or replace the mass air flow sensor
- Replace the PCV valve, hoses or a leaking valve cover gasket
- Restore proper fuel pressure by replacing the pump, filter or regulator
- Clean or replace clogged bank 2 injectors
- Repair bank 2 exhaust leaks
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
P0174, usually paired with P0171, is commonly reported on V6 and V8 engines from Ford, GM, Toyota and Nissan, often from intake gasket leaks, PCV system leaks or MAF contamination; definitions can vary by manufacturer; check factory service information.
Related codes & warning lights
P0174 FAQ
What does code P0174 mean?
P0174 means the engine computer has reached its limit adding fuel on bank 2, the side opposite cylinder 1, because that bank is receiving too much air or too little fuel. The standard definition is "System Too Lean (Bank 2)."
Can I drive with a P0174 code?
In most cases you can drive briefly if the engine runs normally, but lean running can lead to hesitation, misfires and extra heat in the combustion chambers. Have it diagnosed within days, and stop driving if the check engine light begins flashing.
Why would only bank 2 be lean?
A problem that affects only one side, such as an intake manifold gasket leak on bank 2, a cracked vacuum line near that side, clogged bank 2 injectors or a bank 2 exhaust leak ahead of the oxygen sensor, will make that bank lean while bank 1 stays normal.
Why do P0171 and P0174 so often appear together?
Both banks share the same air metering, fuel pump and most of the intake system. A dirty MAF sensor, large vacuum leak or low fuel pressure leans out both sides, so both codes set together.
Can a bad oxygen sensor cause P0174?
It is possible, but less common. A sensor that falsely reads lean can make the computer add fuel unnecessarily, so verify the sensor responds to a rich change before assuming the engine is truly lean.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.