Failed heater element inside the bank 1 sensor 1 air-fuel ratio sensor, which is the most common cause on higher-mileage Nissans; Corroded, chafed, or broken wiring in the heater circuit between the sensor and the engine computer; Blown fuse or faulty relay that supplies power to the sensor heater circuit; Loose or contaminated sensor connector pins causing intermittent heater current; Engine computer driver circuit fault for the heater control, though this is far less common; A replacement sensor of the wrong type or with a damaged heater from poor installation

DTC codes / Nissan codes / P1166

P1166 · NissanHO2S11 Heater Circuit Fault Bank 1 Sensor 1

Q: What does code P1166 mean?

HO2S11 Heater Circuit Fault Bank 1 Sensor 1. P1166 on a Nissan means the engine computer has detected a problem with the electrical heater circuit inside the upstream air-fuel ratio sensor on bank 1, which is the sensor before the catalytic converter on the cylinder bank that contains cylinder number one. The heater element warms the sensor quickly after a cold start so the computer can enter closed-loop fuel control sooner, and the code sets when the computer sees heater current or voltage outside the expected range during its self-test.

P1166 on a Nissan means the engine computer has detected a problem with the electrical heater circuit inside the upstream air-fuel ratio sensor on bank 1, which is the sensor before the catalytic converter on the cylinder bank that contains cylinder number one. The heater element warms the sensor quickly after a cold start so the computer can enter closed-loop fuel control sooner, and the code sets when the computer sees heater current or voltage outside the expected range during its self-test.

SystemPowertrain

Code typeNissan specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other symptoms besides the warning light
A slightly longer warm-up period before the engine runs smoothly, especially on cold mornings
Marginally higher fuel consumption during short trips because the system stays in open-loop longer
Occasional rough idle or hesitation right after a cold start that clears as the engine warms
In rare cases, a stored pending code or a freeze-frame showing the fault occurred during a cold start

Common causes, most likely first

Failed heater element inside the bank 1 sensor 1 air-fuel ratio sensor, which is the most common cause on higher-mileage Nissans
Corroded, chafed, or broken wiring in the heater circuit between the sensor and the engine computer
Blown fuse or faulty relay that supplies power to the sensor heater circuit
Loose or contaminated sensor connector pins causing intermittent heater current
Engine computer driver circuit fault for the heater control, though this is far less common
A replacement sensor of the wrong type or with a damaged heater from poor installation

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm the code set during a cold start and check for related heater circuit codes
Inspect the sensor connector and the harness for corrosion, chafing, or loose pins, and repair any damaged wiring
Check the heater circuit fuse and relay, and verify battery voltage at the heater supply wire with the key on
Measure the heater element resistance at the sensor connector and compare it to the Nissan specification for that engine
Check heater current with a low-amp clamp or measure voltage drop across the heater circuit while the engine is cold
If the heater element is open or out of specification, replace the bank 1 sensor 1 air-fuel ratio sensor with the correct Nissan part
Clear the code, perform a cold-start drive cycle, and verify the monitor completes without the code returning

What Nissan Techs Check Before Swapping the Sensor

A P1166 can set from a heater circuit that only fails when cold, so testing the sensor resistance after the engine has warmed up can falsely show a good part and lead to a misdiagnosis.
Nissan air-fuel ratio sensors are not the same as conventional oxygen sensors, and fitting a generic oxygen sensor in that position often causes heater codes and poor fuel control.
Corrosion inside the connector is a frequent cause on older Nissans, and simply cleaning the pins and applying dielectric grease can cure the code without replacing the sensor.
The heater circuit shares power with other engine management components on some models, so a blown fuse may point to a short elsewhere rather than a failed sensor.
A P1166 does not always mean the sensor is dead, because a weak battery or charging system fault can drop heater voltage during cranking and set the code intermittently.

Can I keep driving with P1166?

You can usually keep driving with P1166 because the engine will still run, but the sensor will take longer to warm up and fuel economy and cold-start emissions may suffer. Avoid long periods of short cold-start trips and have the circuit checked soon, especially if the check engine light flashes or the engine runs rough.

Tools that help

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Guidance is general and written for Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.