Common Checks
- Check for vacuum leaks common to both banks, then bank-specific intake gasket or hose leaks.
- Inspect MAF readings and the air inlet path.
- Check fuel pressure if both banks are lean.
Diagnostic trouble code
P0174 System Too Lean, Bank 2
The PCM is adding too much fuel on bank 2 because the mixture is lean.
Fuel Trim & Mixture CodesCommon Repairs
- Repair vacuum leaks, PCV hose leaks, or loose intake clamps.
- Clean or replace a contaminated MAF sensor.
- Repair fuel delivery issues when pressure or volume is low.
Mustang Notes
- P0171 and P0174 together usually point to an air-metering or fuel-delivery issue affecting the whole engine.
Model-Year Applicability
Listed for 1996 and newer traditional gasoline Mustang pages in this first-pass catalog. Engine, calibration, and Ford-specific codes may narrow that range as more service data is added.