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P0174 — Fuel System Too Lean (Bank 2)

P0174 is the Bank 2 counterpart of P0171. It is set when the engine control module sees long-term fuel trim on Bank 2 driven beyond approximately +25 %. The ECM is adding the maximum allowed amount of fuel and the Bank 2 oxygen sensor still reports lean. Because P0174 only applies to V-engines and engines with separate exhaust banks, whether P0174 appears alongside P0171 tells you a lot about the root cause.

P0174 means fuel system too lean (bank 2). A vehicle usually stays drivable short-term with this code, but it should be diagnosed promptly. The most common cause is vacuum leak specific to bank 2 (intake gasket, vacuum tee, brake-booster tee) (typically $80–$600). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: moderate powertrain Safe to drive (short term)

Reviewed by MECH AI Editorial · Last verified

What does P0174 mean?

P0174 is the Bank 2 counterpart of P0171. It is set when the engine control module sees long-term fuel trim on Bank 2 driven beyond approximately +25 %. The ECM is adding the maximum allowed amount of fuel and the Bank 2 oxygen sensor still reports lean. Because P0174 only applies to V-engines and engines with separate exhaust banks, whether P0174 appears alongside P0171 tells you a lot about the root cause.

What are the symptoms of P0174?

What causes P0174?

Cause Likelihood Estimated repair (USD)
Vacuum leak specific to Bank 2 (intake gasket, vacuum tee, brake-booster tee) Most common $80–$600
Cracked plastic intake manifold on V-engines (common on Ford and Chrysler V6/V8s) Common $250–$900
Bank 2 fuel injectors clogged or under-delivering Common $150–$1,200
Bank 2 upstream O2 sensor lazy or biased lean Common $150–$450
Bank 2 exhaust leak upstream of the front O2 sensor Occasional $100–$500
Weak fuel pump or clogged filter (both banks lean — P0171 also present) Occasional $80–$900
PCV system fault drawing extra air into Bank 2 Occasional $30–$200

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0174?

In most cases a vehicle stays drivable for short trips with P0174 active, but you should diagnose and repair it promptly. This is a moderate-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on your specific make and model.

How to diagnose P0174

  1. Determine whether P0171 is also present

    Pull all codes. If P0174 sets alone, the cause is on Bank 2 specifically — an intake leak on that side, injectors on that side, or the Bank 2 O2 sensor. If P0171 and P0174 set together, the cause is something affecting the whole engine: low fuel pressure, MAF issue, large vacuum leak.

    Tools: Scan tool

  2. Identify the Bank 2 side of the engine

    On most transverse V6s Bank 2 is the bank closest to the radiator. On Ford modular V8s Bank 2 is the passenger side. On GM truck V8s Bank 2 is the passenger side. Confirm in the service manual before pulling parts.

    Tools: Vehicle-specific service information

  3. Smoke-test the Bank 2 intake side

    With smoke in the intake, focus on the Bank 2 intake runner gaskets, the vacuum lines that feed Bank 2 specifically, and the brake booster line if it tees into Bank 2. Cracked plastic intake manifolds on Ford 4.6 V8s, Chrysler 4.0 inline-6, and several GM engines are classic Bank-2-specific P0174 causes.

    Tools: EVAP / intake smoke machine, Flashlight and mirror

  4. Compare Bank 1 vs Bank 2 fuel trims

    With the engine warm, read Bank 1 LTFT and Bank 2 LTFT simultaneously. A 10 %+ difference between banks isolates the problem to the bank with the higher positive number.

    Tools: Scan tool with multi-PID display

  5. Test Bank 2 injectors for low flow

    Run the scan tool injector balance test on Bank 2 injectors only. An injector that does not produce as much pressure drop as its peers is under-delivering fuel and causing the bank-specific lean condition.

    Tools: Scan tool with injector balance

How do I fix P0174?

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P0174: frequently asked questions

What does diagnostic trouble code P0174 mean?

P0174 is the Bank 2 counterpart of P0171. It is set when the engine control module sees long-term fuel trim on Bank 2 driven beyond approximately +25 %. The ECM is adding the maximum allowed amount of fuel and the Bank 2 oxygen sensor still reports lean. Because P0174 only applies to V-engines and engines with separate exhaust banks, whether P0174 appears alongside P0171 tells you a lot about the root cause.

What are the symptoms of P0174?

Check Engine Light is illuminated. Rough idle, especially when cold. Hesitation or stumble on light acceleration. Reduced fuel economy. Mild power loss. Possible whistling vacuum-leak sound

What causes P0174?

Vacuum leak specific to Bank 2 (intake gasket, vacuum tee, brake-booster tee) (most-common). Cracked plastic intake manifold on V-engines (common on Ford and Chrysler V6/V8s) (common). Bank 2 fuel injectors clogged or under-delivering (common). Bank 2 upstream O2 sensor lazy or biased lean (common). Bank 2 exhaust leak upstream of the front O2 sensor (occasional). Weak fuel pump or clogged filter (both banks lean — P0171 also present) (occasional). PCV system fault drawing extra air into Bank 2 (occasional)

Is it safe to drive with P0174?

In most cases a vehicle stays drivable for short trips with P0174 active, but it should be diagnosed and repaired promptly — this is a moderate-severity code. Ignoring it can lead to further damage or a failed emissions test. Specific tolerance varies by make and model.