Engine codes
P0174: system too lean (bank 2)
Only engines with two cylinder banks, V6 and V8 mostly, can set P0174. It means the side without cylinder 1 is running lean even though the computer is adding all the fuel it is allowed to.
P0174: can I drive, and what will the labor cost?
Estimated labor, find and replace a leaking vacuum or pcv hose
$33 to $110
| Labor time (estimate) | 0.3 to 1 h |
| Rate used | $110/h |
| Technician wage, United States (average) | $27.13/h |
| Moderate: fix within weeks Drivable for now; fix within a few weeks, and read the other bank: P0171 at the same time changes the diagnosis. | |
Labor only: parts and the diagnostic fee are not included. Hours are our estimate for a typical car; book times vary by model. Wage: BLS, May 2025.
P0174 is the generic OBD-II code for "system too lean, bank 2". Bank 2 is the row of cylinders opposite cylinder 1 on a V-shaped engine; each bank has its own upstream oxygen sensor and its own fuel trims. The code is set when bank 2's long-term trim reaches the upper limit and the sensor still sees too much oxygen. The first question is whether P0171 is stored as well. When both banks are lean together, the cause is usually upstream of where the banks split: an air flow sensor that under-reads, low fuel pressure from the pump or filter, or a leak at the throttle body or a large vacuum hose. When only bank 2 is lean, look at that side: an intake manifold gasket or hose on bank 2, a restricted injector there, or an exhaust leak ahead of the bank 2 sensor that lets in air and fools it. It is drivable for now; fix it within a few weeks.
Read your fuel trims (from a scanner's live data)
Total trim at idle / 2,500 rpm
+20% / +6%
| Reading: Lean at idle that improves with engine speed: the pattern of a vacuum leak. |
Positive trims mean the computer is adding fuel. This idle-versus-speed comparison is a common shop test, not a rule: confirm with a smoke test or a fuel pressure gauge. Negative values can be typed with a minus sign.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
P0174 at a glance
| Code | P0174 |
| Standard description | System Too Lean (Bank 2) |
| System | Fuel mixture and delivery |
| Severity | Moderate: fix within weeks |
| Common symptoms | hesitation, rough idle, misfire under load |
Finding bank 2 on your engine
Cylinder 1 is on bank 1, and the maker's cylinder numbering shows which side that is. On many transverse V6 engines bank 1 is the rear bank, next to the firewall, and bank 2 faces the radiator; on many longitudinal V8 trucks bank 1 is the driver's side. The P0302 page explains why this numbering trips people up. Getting it wrong sends the search for a leak to the wrong side of the engine.
The exhaust leak trap
An upstream oxygen sensor measures oxygen in the exhaust. If a cracked manifold or a blown gasket lets air in just ahead of it, the sensor reports lean although the cylinders are not, and the computer adds fuel that the engine does not need. That is why a ticking noise from one side of the engine when cold is a useful clue with a single-bank lean code, and why a shop may check the manifold before the intake.
Comparing the two banks
With a scanner, compare long-term trims side by side. Roughly equal high trims on both banks support a shared cause; a large gap supports a bank 2 cause. The fuel trim reader on this page takes one bank at a time, so run it twice. A lean condition that persists can lead to misfires such as P0300, which then need fixing in the right order: lean first.
Likely causes of P0174, in order
| Cause | How often |
|---|---|
| Vacuum leak on the bank 2 side: intake gasket, hose | most frequent |
| MAF sensor reading low (usually with P0171 too) | most frequent |
| Low fuel pressure (usually with P0171 too) | frequent |
| Exhaust leak ahead of the bank 2 upstream sensor | less frequent |
P0174 repairs and labor time
| Repair | Labor (estimate) | At $110/h |
|---|---|---|
| Find and replace a leaking vacuum or PCV hose | 0.3 to 1 h | $33 to $110 |
| Replace intake manifold gasket | 1.5 to 4 h | $165 to $440 |
| Replace the MAF sensor | 0.3 to 0.6 h | $33 to $66 |