Symptom hub
Poor Highway MPG: Is the Converter Locking, or Is the Engine Really the Problem?
Poor highway fuel economy is not always an engine-mixture story. If the engine revs higher than normal at cruise or lockup never arrives, the transmission and torque-converter branch deserves a front seat.
Likely related codes
Start your diagnostic path here
P0171 — System Too Lean (Bank 1) P0172 — System Too Rich (Bank 1) P0420 — Catalyst System Efficiency Below Threshold (Bank 1) P0430 — Catalyst System Efficiency Below Threshold (Bank 2) P0128 — Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) P0741 — Torque Converter Clutch Circuit Performance or Stuck Off P0740 — Torque Converter Clutch Circuit Malfunction P0743 — Torque Converter Clutch Solenoid Circuit Electrical P0744 — Torque Converter Clutch Circuit Intermittent P0126 — Insufficient Coolant Temperature for Stable Operation P2761 — Torque Converter Clutch Pressure Control Solenoid Control Circuit/Open