P0174 means System Too Lean Bank 2. The engine control module (ECM/PCM) has detected that the air-fuel mixture on Bank 2 is too lean and that the fuel correction has reached or exceeded its expected limit.
In simple terms, the engine computer is adding more fuel than normal because it believes Bank 2 has too much air or not enough fuel. The actual cause may be an intake leak, MAF problem, low fuel pressure, injector problem, exhaust leak, or an issue with the air-fuel feedback system. 1
Fault Code Description
P0174 = System Too Lean Bank 2.
This generic OBD-II code indicates that the ECM/PCM has detected excessive fuel correction on Bank 2. Bank 2 is the cylinder bank that does not contain cylinder number 1 on engines with multiple cylinder banks. 2
P0174 is commonly found on V6, V8 and other multi-bank engines. Inline engines normally do not have a separate Bank 2.
Symptoms of P0174
Check Engine Light: The MIL may illuminate when the ECM detects excessive fuel correction on Bank 2.
Rough Idle: The engine may idle unevenly because the air-fuel mixture is not being controlled correctly.
Poor Acceleration: The vehicle may hesitate or feel weak when accelerating.
Engine Misfire: A severe lean condition can contribute to misfires.
Reduced Engine Power: Some vehicles may experience noticeable loss of power.
Poor Fuel Economy: The ECM may continuously add fuel in an attempt to correct the lean condition.
Common Causes of P0174
Vacuum or Intake Leak: Unmetered air entering the engine can create a lean condition, especially around Bank 2 intake runners or vacuum connections.
Dirty or Faulty MAF Sensor: An inaccurate MAF reading can cause the ECM to calculate the wrong amount of fuel.
Low Fuel Pressure: A weak fuel pump, restricted filter or fuel-delivery problem can prevent the injectors from supplying enough fuel.
Restricted or Faulty Injector: A clogged or contaminated injector on Bank 2 can reduce fuel delivery to one or more cylinders.
Exhaust Leak: An exhaust leak near the upstream oxygen sensor can allow outside air into the exhaust stream and make the mixture appear lean.
PCV or EVAP Problems: A leaking PCV system or purge valve can introduce unwanted air into the intake system.
Oxygen or Air-Fuel Sensor Problem: A faulty sensor can report an incorrect mixture condition, although the sensor should not be replaced without testing.
P0174 Bank 2: Which Side Is Bank 2?
Bank 2 is the engine bank that does not contain cylinder number 1.
The exact physical location depends on the engine design and manufacturer. Therefore, do not assume that Bank 2 is always the driver's side or passenger side.
For accurate identification, check the vehicle's firing order, cylinder numbering and manufacturer service information.
How to Fix P0174
1. Check Fuel Trim Data
Connect a scan tool and check STFT and LTFT for both banks.
If Bank 2 has significantly higher positive fuel trims than Bank 1, the problem may be localized to Bank 2. If both banks show high positive fuel trims, investigate components shared by both banks, such as the MAF sensor, fuel supply or a common intake leak. 4
2. Compare Idle and Cruise Fuel Trims
Check the fuel trims at idle and again while cruising.
If the fuel trims are very high at idle but improve significantly at higher RPM, an intake or vacuum leak becomes more likely. If the trims remain high under different operating conditions, investigate MAF accuracy and fuel delivery.
3. Inspect the Intake System
Inspect the intake boot, vacuum hoses, PCV hoses, intake manifold gaskets and connections around Bank 2.
A smoke test can help locate leaks that cannot be found through visual inspection.
4. Check the MAF Sensor
Verify that the MAF reading is reasonable for the engine speed and load.
A contaminated or inaccurate MAF sensor can cause incorrect airflow calculations and abnormal fuel trims. Do not replace the MAF sensor simply because P0174 is stored.
5. Check Fuel Pressure
Measure fuel pressure according to the manufacturer's specification.
Low fuel pressure can cause insufficient fuel delivery and produce a lean condition. Check fuel pressure under the operating conditions where the fault occurs.
6. Check the Injectors
Inspect the Bank 2 injectors for restriction, contamination or electrical problems.
An injector balance test can help determine whether one or more injectors are delivering less fuel than expected.
7. Check for Exhaust Leaks
Inspect the exhaust manifold and exhaust connections near the Bank 2 upstream oxygen or air-fuel sensor.
An exhaust leak before or near the sensor can allow outside oxygen into the exhaust and distort the sensor feedback. 5
P0174 and P0171 Together
If P0174 and P0171 appear together, both engine banks are reporting lean conditions.
This combination can point toward a problem affecting the entire engine rather than only Bank 2. Common areas to investigate include the MAF sensor, fuel pressure, fuel delivery and a large intake or vacuum leak upstream of the point where the intake system divides between the banks. 6
P0174 BMW
On BMW vehicles, P0174 still indicates a lean condition on Bank 2, but the actual cause can involve unmetered air, crankcase ventilation, MAF measurement, fuel delivery or oxygen-sensor feedback.
BMW diagnosis should therefore include checking intake and crankcase ventilation leaks before replacing an oxygen sensor.
P0174 Chevrolet
On Chevrolet applications, inspect the intake system, MAF sensor, fuel pressure, injectors and Bank 2 oxygen-sensor feedback.
If P0171 and P0174 are stored together, concentrate first on faults that can affect both banks.
P0174 Toyota
On Toyota vehicles, compare Bank 1 and Bank 2 fuel trims and verify MAF or MAP information, fuel pressure and air-fuel sensor operation according to the engine configuration.
The exact diagnostic procedure and sensor specifications vary between Toyota engines.
P0174 Ford
On Ford applications, possible causes include vacuum leaks, MAF problems, low fuel pressure, restricted fuel supply, injector problems, PCV leaks and exhaust leaks near the oxygen sensor. 7
Freeze-frame information and fuel-trim data can help identify whether the problem occurs at idle, cruise or under load.
P0174 GMC
On GMC vehicles, check whether the code occurs alone or together with a Bank 1 lean code. If both banks are lean, inspect shared air and fuel systems before concentrating on Bank 2 components.
Which O2 Sensor Is P0174?
P0174 concerns the mixture condition detected for Bank 2, generally using the upstream air-fuel or oxygen-sensor feedback for that bank.
Sensor 1 normally refers to the upstream sensor located before the catalytic converter, while Sensor 2 normally refers to the downstream sensor after the catalytic converter. 8
However, P0174 does not automatically mean the O2 sensor is defective. The sensor may be correctly reporting a real lean condition caused by an intake leak or fuel-delivery problem.
Repair Cost for P0174
The repair cost depends entirely on the component causing the lean condition.
Vacuum or Intake Leak: approximately $50–$300+ depending on the leak location and labor.
MAF Sensor: approximately $100–$400+ depending on the vehicle.
Oxygen or Air-Fuel Sensor: approximately $100–$400+ depending on the application.
Fuel System Repair: the cost can vary considerably if the problem involves a fuel pump, pressure regulator, injectors or restricted fuel supply.
These are general estimates only. Actual repair cost depends on the vehicle, engine, parts and local labor rates.
Common Repair Mistakes
Replacing the O2 Sensor First: P0174 does not automatically mean the oxygen sensor has failed.
Replacing the MAF Without Testing: A MAF sensor can cause P0174, but fuel-trim and airflow data should be checked first.
Ignoring Vacuum Leaks: Unmetered air is one of the important causes of lean fuel trims.
Checking Only the Trouble Code: Freeze-frame data, STFT and LTFT can provide much more useful diagnostic information than the code alone.
Is P0174 Serious?
P0174 should not be ignored. A mild lean condition may allow the vehicle to continue running, but a severe or prolonged lean condition can cause rough running, misfires, reduced performance and increased engine or emissions-system stress.
If the engine is misfiring, overheating, losing significant power or running very poorly, avoid unnecessary driving until the cause is diagnosed.
Can I Drive With P0174?
If the engine is running normally and there are no severe symptoms, limited driving may be possible. However, the underlying lean condition should be diagnosed as soon as practical.
A vehicle with severe misfires, major loss of power or unstable engine operation should not be driven unnecessarily.
FAQ About P0174
What does P0174 mean?
P0174 means System Too Lean Bank 2. The ECM has detected excessive fuel correction while trying to compensate for a lean mixture on Bank 2.
How do I fix code P0174?
Start by checking fuel trims, then inspect for intake and vacuum leaks, verify MAF readings, test fuel pressure, inspect injectors and check the upstream oxygen or air-fuel sensor feedback.
What is the most common cause of P0174?
Common causes include unmetered air leaks, MAF measurement problems, fuel-delivery issues and injector problems. The most likely cause depends on whether P0174 appears alone or with P0171.
Where is Bank 2 located?
Bank 2 is the cylinder bank that does not contain cylinder number 1. Its physical location depends on the engine design and vehicle.
Which O2 sensor is P0174?
P0174 relates to the mixture condition of Bank 2 and normally involves upstream oxygen or air-fuel sensor feedback. It does not necessarily mean that the sensor itself is defective.
Can a bad MAF sensor cause P0174?
Yes. An inaccurate MAF reading can cause the ECM to calculate incorrect airflow and fuel delivery, resulting in abnormal fuel trims.
Can a vacuum leak cause P0174?
Yes. A vacuum or intake leak can introduce unmetered air and cause the engine to run lean.
Can P0174 cause a misfire?
Yes. A sufficiently lean mixture can contribute to unstable combustion and misfires, especially when the condition becomes severe.
Related Codes
P0171 – System Too Lean Bank 1
P0172 – System Too Rich Bank 1
P0173 – Fuel Trim Malfunction Bank 2
P0175 – System Too Rich Bank 2
Final Result
P0174 is a System Too Lean Bank 2 fault code. The code identifies the condition, not a specific failed part.
The best diagnosis starts with STFT and LTFT data, followed by intake-leak testing, MAF verification, fuel-pressure testing, injector checks and oxygen or air-fuel sensor evaluation.
If P0174 appears together with P0171, investigate faults that can affect both banks before replacing individual Bank 2 components.