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P0174 P0xxx · 动力总成（P） 中严重度
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.
严重程度说明： 中——已影响行驶或排放，请本周内安排检修
你会注意到的故障现象
- Lean misfire under load
- Hesitation
- High NOx on emissions test
- Possible pinging
常见原因
按可能性从高到低排列——从最上面开始查。
- 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
如何排查
先做花钱最少、侵入最小的检查——大多数这类码不是零件问题。
- ✓ 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.
维修方案
- Repair the intake leak
- Replace the fuel pump or filter if pressure is low
- Repair the exhaust leak
- Clean the MAF
P0174 —— 常见问题
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.