OBD-II Diagnostic Trouble Code
P0174 — System Too Lean (Bank 2)
P0174 means bank 2 fuel trims have gone positive beyond the ECM's limit. The ECM is adding the most fuel it can and still sees a lean mixture on bank 2. It applies to V-engine gasoline trucks. When P0171 and P0174 are set together, the cause usually affects both banks, such as fuel supply, mass airflow sensor or a common vacuum leak.
Severity 3/5
Less common on commercial trucks
Service this week
Severity
Service this week
System Too Lean (Bank 2)
Code
P0174
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Less common
What this means for truckers
Service within a few days. Performance is likely degraded. Continuing to drive without service risks additional component damage.
Before you replace parts — try this first
P0174 on the Fuel system is most often vacuum leak on the bank 2 side, such as an intake gasket, pcv hose or vacuum line — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Check-engine light is on. You may also notice hesitation, rough idle, lean misfires on bank 2 cylinders and loss of power under load. Symptoms are often worse when the engine is cold or when the truck is loaded.
Common causes
- CommonVacuum leak on the bank 2 side, such as an intake gasket, PCV hose or vacuum line ($50–$500)
- CommonLow fuel pressure or volume (especially with P0171) ($100–$1000)
- CommonMass airflow sensor contaminated or reading low (especially with P0171) ($20–$350)
- OccasionalExhaust leak ahead of the bank 2 upstream sensor ($150–$600)
- OccasionalRestricted injectors on bank 2 ($150–$900)
How to fix
Check whether P0171 is also set. If both banks are lean, test fuel pressure and the mass airflow sensor first. If only bank 2 is lean, focus on that side.
When to use: First step
Smoke test the intake, concentrating on the bank 2 side.
When to use: When trims are high at idle
Inspect the bank 2 exhaust manifold and gaskets for leaks.
When to use: When there are no intake leaks
Run an injector balance or flow test on bank 2.
When to use: When the lean condition is limited to bank 2 and the other checks pass
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0100 — Mass or Volume Air Flow Circuit
- → P0101 — Mass or Volume Air Flow Circuit Range/Performance
- → P0102 — Mass or Volume Air Flow Circuit Low Input
- → P0103 — Mass or Volume Air Flow Circuit High Input
- → P0104 — Mass or Volume Air Flow Circuit Intermittent
Frequently Asked Questions
Can I drive with code P0174?
P0174 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0174 on a commercial truck?
Total repair cost ranges $20–$1000 depending on the root cause. The cheapest fix is usually the first one listed below — Vacuum leak on the bank 2 side, such as an intake gasket, PCV hose or vacuum line — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0174 fail a DOT inspection?
P0174 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0174 and related codes?
P0174 is closely related to: P0100 (Mass or Volume Air Flow Circuit), P0101 (Mass or Volume Air Flow Circuit Range/Performance), P0102 (Mass or Volume Air Flow Circuit Low Input), P0103 (Mass or Volume Air Flow Circuit High Input). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0174 is set without the companions, the issue is more isolated.
How do I prevent P0174 from coming back after a repair?
For P0174 (System Too Lean (Bank 2)), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.