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P0174 System Too Lean (Bank 2)

Same lean condition as P0171, but on the engine's other cylinder bank — only V-shaped and flat engines can set this one.

Fuel & air

Bank 2 is the side of a V6, V8 or flat engine that does not contain cylinder 1. P0174 means the ECU ran out of fuel trim trying to correct a lean condition on that bank. Which banks are affected is itself the diagnosis: P0174 alone points to something local to bank 2, while P0171 and P0174 together point to something both banks share — and that combination is one of the most useful clues in the whole fuel-trim family.

Diagnose P0174 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you need

Can I keep driving?

Driveable

Yes, though expect rough idle and hesitation. Go easy under heavy load.

How serious

Moderate. As with P0171, sustained lean running is hard on valves, pistons and the converter.

Symptoms you'll notice

What causes P0174

Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.

01

Vacuum leak on bank 2

A leaking intake manifold gasket or a cracked hose feeding only that bank. If P0174 appears without P0171, look for something physically on that side of the engine.

02

Shared cause with bank 1

When P0171 and P0174 are both stored, stop looking for two separate leaks. Something common to both banks is responsible: the mass airflow sensor, fuel pressure, the PCV system, or a leak at the throttle body or the base of the intake plenum. This is the single most valuable inference this code offers.

03

Weak fuel delivery

A failing pump or clogged filter affects both banks, but marginal fuel pressure can trip one bank's threshold before the other.

04

Failing bank 2 upstream oxygen sensor

A biased sensor on that bank reports lean when the mixture is correct. Compare bank 1 and bank 2 sensor readings against each other on live data.

05

Exhaust leak ahead of the bank 2 sensor

A cracked manifold on that side draws in air and reads lean.

How to diagnose it

  1. Note whether P0171 is stored too. Both banks means a shared cause; bank 2 alone means look at that side of the engine.
  2. Compare bank 1 and bank 2 fuel trims on live data — the difference between them tells you how localised the fault is.
  3. Inspect the bank 2 intake gasket, hoses and connections specifically.
  4. Clean the MAF and check fuel pressure if both banks are affected.
  5. Check for exhaust leaks on the bank 2 manifold.

Parts you might need

Tools for the job

Related trouble codes

Get the parts list for your vehicle Ranked causes, tutorials and live part prices for your exact year, make and model

Fitment matters. Causes and parts above are the common cases for P0174 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.