P0174: System Too Lean Bank 2
What Does P0174 Mean?
P0174 is a diagnostic trouble code indicating: System Too Lean Bank 2. This code relates to the fuel and air metering system. It has been reported in NHTSA complaints across 14 different vehicle models.
Fuel trim is the ECU's real-time adjustment to fuel delivery. Short-term fuel trim (STFT) reacts immediately to O2 sensor feedback, while long-term fuel trim (LTFT) is a learned correction stored in memory. When LTFT exceeds approximately ±25%, the ECU sets a fuel trim code because it's run out of adjustment range. Positive fuel trim means the ECU is adding fuel (lean condition), negative means it's subtracting fuel (rich condition). Understanding fuel trims is key to diagnosing these codes — they tell you the direction and magnitude of the problem.
Fuel trim is the ECU's real-time adjustment to fuel delivery. Short-term fuel trim (STFT) reacts immediately to O2 sensor feedback and fluctuates constantly. Long-term fuel trim (LTFT) is a learned correction stored in memory that compensates for gradual changes like wear and altitude. When LTFT exceeds approximately ±25%, the ECU has run out of adjustment range and sets a fuel trim code. Understanding the difference between STFT and LTFT is key: STFT shows what's happening NOW, LTFT shows the average correction over many drive cycles. At idle, high positive fuel trims suggest vacuum leaks. At cruise, high positive trims suggest fuel delivery issues (pump, filter, pressure). Common affected vehicles: Any vehicle — fuel trim codes are universal and affect all makes equally.
**Real-World Diagnostic Walkthrough:** P0174 is the Bank 2 equivalent of P0171. If both P0171 and P0174 appear together, the cause is shared between both banks: intake manifold vacuum leak (the most common dual-bank cause), dirty MAF sensor, low fuel pressure, or a large PCV system leak. The fact that both banks show lean simultaneously eliminates bank-specific causes (individual O2 sensors, exhaust leaks on one side). Start with a smoke test ($80-$150) to find vacuum leaks, then clean the MAF sensor ($8 for cleaner). If you don't have access to a smoke machine, spray carb cleaner around intake gaskets and vacuum hoses while the engine idles — if the idle changes, you found a leak. Check fuel pressure with a gauge — low pressure affects both banks equally. On V6 Ford vehicles, the intake manifold gaskets are a known failure point causing dual-bank lean codes.
Symptoms of P0174
- ⚠️ check engine light
- ⚠️ rough idle
- ⚠️ hesitation on acceleration
- ⚠️ poor fuel economy
- ⚠️ possible misfires
Common Causes
- 🔍 Vacuum leak (common to both banks if P0171 also present)
- 🔍 Dirty or faulty MAF sensor
- 🔍 Low fuel pressure
- 🔍 Clogged fuel injectors on Bank 2
- 🔍 Exhaust leak near Bank 2 O2 sensor
P0174 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"THE FIRST INDICATION WAS THE CRL CAME ON WITH CODES P0171 AND THEN P0174. WHEN PRESSING THE BRAKE PEDAL DOWN, THERE IS A HISSING NOISE AND THE BRAKE PEDAL WOULD BASICALLY GO ALL THE WAY TO THE FLOOR. IT SOUNDS AS IF THIS HAS HAPPENED QUITE A BIT WITH THIS MODEL AND SHOULD BE LOOKED INTO. THE DEAL"
— Toyota Camry owner, 10/20/2012
"FIRST NOTICED THE PROBLEM ON 11/10/2014 WHEN APPROACHING A STOP LIGHT. THE RAV4 TOOK LONGER THAN NORMAL TO COME TO A STOP WITH GREATER FORCE REQUIRED TO STOP. ONCE FULLY STOPPED, THE VEHICLE WAS IDLING WITH LOW RPM'S (~500) AND THE CHECK ENGINE LIGHT TURNED ON ALONG WITH VSC AND TRAC LIGHTS. WAS "
— Toyota Rav4 owner, 11/10/2014
"Today (8/26/2025) my wife experienced the engine light kicked on and that the AWD system needed to be checked. After fueling up it made knocking noises and difficulty starting, and took two times to start up. Ran an OBD scan and this is what it says, which is related to fuel pump low pressure. P11"
— Toyota Highlander owner, 08/26/2025
Source: NHTSA Complaints Database
Most Reported Vehicles for P0174
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | TOYOTA HIGHLANDER | |
| 2 | TOYOTA CAMRY | |
| 3 | TOYOTA RAV4 | |
| 4 | TOYOTA AVALON | |
| 5 | FORD F-150 | |
| 6 | FORD RANGER | |
| 7 | CHEVROLET SILVERADO | |
| 8 | CHEVROLET TRAVERSE | |
| 9 | NISSAN MAXIMA | |
| 10 | JEEP CHEROKEE | |
| 11 | SUBARU OUTBACK | |
| 12 | GMC TERRAIN | |
| 13 | MERCEDES-BENZ E-CLASS | |
| 14 | CHRYSLER PACIFICA |
P0174 Reports by Vehicle
Detailed NHTSA complaint analysis for each vehicle model.
Diagnostic Tips
- Read STFT and LTFT at idle AND at 2500 RPM. If both are high at idle but normal at higher RPM, suspect a vacuum leak. If both are high everywhere, suspect fuel delivery (pump, filter, pressure).
- Smoke test the intake system — this is the fastest way to find vacuum leaks that cause lean fuel trims.
- Check fuel pressure with a gauge. Low pressure causes lean codes; high pressure causes rich codes.
- If only one bank shows abnormal fuel trims, the cause is likely isolated to that bank (O2 sensor, exhaust leak, injector on that bank).
Common Mistakes to Avoid
- ❌ Replacing O2 sensors based on fuel trim codes — the sensors are correctly reporting the problem, not causing it.
- ❌ Not checking fuel trims before starting repairs — fuel trim data tells you exactly which direction to investigate.
- ❌ Clearing codes without fixing the root cause — LTFT relearns within a few drive cycles and the code returns.
Frequently Asked Questions
Is P0174 the same as P0171?
Can I drive with P0174?
What are normal fuel trim values?
How do I read fuel trim data?
What To Do Next
Possible Fixes
- 🔧 Inspect and repair vacuum leaks
- 🔧 Clean MAF sensor
- 🔧 Clean or replace fuel injectors
- 🔧 Replace fuel pump or filter
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.