AutoCodes – Generic – P1166

P1166 Code - Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction

Quick Answer

The Air/Fuel Ratio (A/F) sensor 1 is installed in the exhaust system and detects oxygen content in the exhaust gas. Common causes include Faulty Air/Fuel Ratio Sensor 1, Air/Fuel Ratio Sensor 1 harness is open or shorted, Air/Fuel Ratio Sensor 1 circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P1166 indicates Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction.
Common causes: Common causes include Faulty Air/Fuel Ratio Sensor 1, Air/Fuel Ratio Sensor 1 harness is open or shorted, Air/Fuel Ratio Sensor 1 circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 12,297

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 04, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P1166 Description

The Air/Fuel Ratio (A/F) sensor 1 is installed in the exhaust system and detects oxygen content in the exhaust gas. The A/F sensor transmits output voltage to the Engine Control Module (ECM). A heater for the sensor element is embedded in the A/F sensor (sensor 1). It is activated and heats the sensor to stabilize and speed the detection of oxygen content by controlling current flowing through the heater. An increase in the current levels off as the applied voltage to the element electrode reaches a certain range because the amount of oxygen which is led through the diffusion layer is limited. The current amperage is proportional to oxygen content in the exhaust gas, so the air/fuel ratio is detected by the measurement of the current amperage. The ECM compares a set target air/fuel ratio with the detected air/fuel ratio and controls the fuel injection timing.
If the A/F sensor (sensor 1) voltage is low, the air/fuel ratio is lean, and the ECM uses A/F feedback control to issue a Rich command. If the A/F sensor (sensor 1) voltage is high, the air/fuel ratio is rich, and the ECM uses A/F feedback control to issue a Lean command.

OBDII Code P1166 - Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction - AutoCodes.com — P1166 Code - Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction

What does this mean?

What are the Possible Causes of the DTC P1166?

Faulty Air/Fuel Ratio Sensor 1
Air/Fuel Ratio Sensor 1 harness is open or shorted
Air/Fuel Ratio Sensor 1 circuit poor electrical connection

How to Fix the DTC P1166?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1166 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Information for Specific Makes

P1166 Acura — Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction
P1166 Audi — Bank 1 Long Term Fuel Trim Range 2 Rich Upper Limits Exceeded
P1166 Honda — Air/Fuel Ratio Sensor 1 Heater Circuit Malfunction
P1166 Hyundai — O2 Sensor System Lambda Controller at the Limit Bank 1
P1166 Infiniti — Heated Oxygen Sensor 2 Minimum Voltage Monitoring Bank 2
P1166 KIA — O2 Sensor System Lambda Controller at the Limit Bank 1
P1166 Nissan — Heated Oxygen Sensor 2 Minimum Voltage Monitoring Bank 2
P1166 Suzuki — HO2S Circuit Low Voltage During Power Enrichment Sensor 1
P1166 Volkswagen — Bank 1 Long Term Fuel Trim Range 2 Rich Upper Limits Exceeded

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.