Possible causes

– Air leakage or restriction in intake or exhaust system
– Dirty engine oil or oil level too high
– Front HO2S or MAFS contamination
– Fuel system
– EVAP system
– Faulty sensor signals

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1166 HYUNDAI Description

The Lambda closed-loop control system is included in the engine’s control system. The control system regulates the lambda upstream with the HO2S signal. Rich mixtures generate high concentrations of CO, H2, and HC. Lean mixtures generate the high concentrations of NOx, and free oxygen.

If the lambda controller reaches the maximum or minimum threshold, then feedback control is no longer possible and emissions will be increased. The ECM sets DTC P1166 if no proportional fuel adaptation occurs for a defined time after the lambda controller has reached its minimum or maximum threshold.