P1166 — Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Electrical Problem
CAUTIONIs it safe to drive? Drive gently and get it looked at soon — it can worsen or fail inspection.
What P1166 means
This is a manufacturer-specific code — its meaning depends on the vehicle’s make (see below).
What P1166 means on specific makes
Heads up: P1166 is a manufacturer-specific code, so the same number means different things by make.
Honda / Acura CAUTION
Electrical fault in the upstream A/F sensor's heater circuit so the sensor can't reach operating temperature. Very common Honda/Acura code; the A/F sensor is a wear item.
- Failed upstream A/F sensor ($90-250)
- Blown A/F heater fuse
- Connector/wiring fault
Check first: Check heater fuse and sensor heater resistance; P1166 with P1167 together usually means just replace the A/F sensor.
Source: hondacodes.wordpress.com, 2carpros.com/questions/p1166-p1167, hondaaccordforum.com
Hyundai / Kia CAUTION
Hyundai/Kia-specific. The wideband A/F (lambda) sensor on bank 1 is reading at its control limit or the heater circuit is faulty — the ECM can't trim mixture properly. Often the upstream A/F sensor itself.
- Upstream air/fuel ratio sensor failed ($80-250)
- A/F sensor heater circuit / fuse / wiring
- Exhaust leak before the sensor
- Vacuum/intake leak skewing mixture
Check first: Check live A/F sensor data and heater circuit resistance. Inspect for exhaust leaks ahead of the sensor before condemning it.
Source: engine-codes.com P1166 Hyundai; AutoCodes P1166; RepairPal P1166/P1167