CodeXOBD

P0174 — System Too Lean (Bank 2)

P0174 means bank 2 is running too lean — too much air or too little fuel. A vacuum leak, weak fuel pump, or dirty fuel injector on bank 2 are the usual causes.

Moderate

The engine may hesitate, idle roughly, or lack power, particularly under load. Long-term lean running can damage the catalytic converter. This code will cause an emissions test failure.

$10–$500Parts, typical range
0.5–3 hLabour
estimateNot a quote · 2026 basis

What P0174 means

P0174 is the bank 2 counterpart of P0171. The module monitors long-term fuel trim — how much it has to add or subtract fuel to maintain the correct air-fuel ratio. When the correction exceeds roughly +25%, the module sets a lean code. On V-engines, each bank has its own trim, so P0174 on bank 2 can coexist with normal trim on bank 1, which narrows the fault to bank 2-specific components.

Technical summary
SystemPowertrain — fuel and air metering
How the fuel mixture is decidedAir passes the mass airflow sensor, then the throttle, into the intake manifold and the cylinder. The module injects fuel to match the measured air, and the upstream oxygen sensor reports the result so it can correct itself. Air entering after the sensor was never measured, which is why a leak downstream of it makes the mixture run lean.Air inAirflow sensormeasures massThrottleCylinderfuel added hereO₂ sensorreports resultAny air entering after the sensor is fuel the module never accounted for

Symptoms you may notice

What causes P0174

Vacuum leak on bank 2

Very likelylow costmoderate

A leaking intake manifold gasket, cracked vacuum hose, or loose connection on bank 2 lets in unmetered air. This is the most common cause.

Low fuel pressure

Likelymedium costmoderate

A weak fuel pump or clogged filter reduces fuel delivery to both banks. When combined with P0171, this is likely.

Dirty or clogged fuel injectors on bank 2

Possiblemedium costmoderate

Restricted injectors on bank 2 reduce fuel delivery on that side only, which explains a bank-specific lean code.

How to diagnose it

1

Check freeze frame data

Check which conditions trigger the code — cold start, idle, or under load. A lean condition at idle points to a vacuum leak; under load points to fuel delivery.

Tools: OBD-II scannerIf it passes: Conditions noted. Continue to step 2.If it fails: Record the conditions for diagnosis.
2

Inspect for vacuum leaks on bank 2

Inspect all vacuum hoses, the intake manifold gasket, and the PCV valve on bank 2. Use a smoke machine or carb cleaner to find leaks.

Tools: Smoke machine or carb cleaner, Inspection lightIf it passes: No leaks found. Continue to step 3.If it fails: Repair the leak, clear the codes, and re-test.
3

Check fuel pressure

Connect a fuel pressure gauge and check pressure at idle and under load. Compare to specification.

Tools: Fuel pressure gaugeExpected: Varies by vehicle — typically 35-65 psiIf it passes: Pressure is correct. Injectors on bank 2 may be the fault.If it fails: Low pressure — check the filter, pump, and regulator.

Related codes

P0171P0172P0173

Common questions

I have both P0171 and P0174 — what does that mean?

Both banks running lean points to a shared cause: low fuel pressure, a clogged filter, a vacuum leak upstream of where the intake splits, or a dirty MAF sensor.

Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)

This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.