Poor Fuel Economy: OBD2 Diagnosis Path

Noticeable MPG drop from rich/lean corrections or cold enrichment. Start with the related code pages below, then use scanner and guide pages to narrow down root cause and reduce unnecessary parts swaps.

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Most Related OBD2 Codes

P0171 · System Too Lean (Bank 1) P0420 · Catalyst System Efficiency Below Threshold (Bank 1) P0128 · Coolant Temperature Below Thermostat Regulating Temperature P0507 · Idle Air Control System RPM High P0401 · Exhaust Gas Recirculation Flow Insufficient Detected

Tip: if your exact code is still unknown, start at OBDHacks scanner input and then return to this symptom cluster for deeper troubleshooting.