P0174 P0xxx · Powertrain (P) Medium severity
System Too Lean (Bank 2)
Bank 2 fuel trims are strongly positive — the ECU is adding fuel because the mixture is too lean on that side of the engine.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Lean misfire under load
- Hesitation
- High NOx on emissions test
- Possible pinging
Common causes
Ordered from most to least likely — start at the top.
- 1 Vacuum leak specific to bank 2
- 2 Weak fuel delivery
- 3 Contaminated MAF
- 4 Exhaust leak before the bank 2 sensor
- 5 Low fuel pressure
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Compare bank 1 and bank 2 trims; a single-bank problem means a local leak or injector.
- ✓ Smoke-test the intake manifold on that bank.
- ✓ Check fuel pressure under load, not just at idle.
- ✓ Look for exhaust leaks before the bank 2 upstream sensor.
Repair options
- Repair the intake leak
- Replace the fuel pump or filter if pressure is low
- Repair the exhaust leak
- Clean the MAF
P0174 — frequently asked questions
Both banks are lean — now what? +
A shared cause: MAF, fuel pressure, or a large vacuum leak after the throttle body.
Can a misfire cause a lean code? +
Yes — an unburned-charge misfire dumps oxygen into the exhaust and the sensor reads it as lean.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.