OBD-IIFuel Trim
Fuel Trim Fault Codes
Short and long-term fuel trim codes indicating rich or lean conditions.
Fuel Trim Codes (1)
Diagnostic Approach — Fuel Trim
- 1
Monitor short-term (STFT) and long-term (LTFT) fuel trims at idle and 2500 RPM.
- 2
LTFT over +10% at idle = vacuum leak. LTFT over +10% at cruise = MAF or fuel delivery.
- 3
Check for vacuum leaks with smoke machine or carburetor cleaner.
- 4
Inspect and clean MAF sensor.
- 5
Test fuel pressure — low pressure causes lean codes across all cylinders.
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