Possible causes

– Faulty Heated Oxygen Sensor Bank 2 Sensor 3
– Heated Oxygen Sensor Bank 2 Sensor 3 harness is open or shorted
– Heated Oxygen Sensor Bank 2 Sensor 3 circuit poor electrical connection

Tech notes

Replacing the O2 Sensor 3 usually takes care of the problem

When is the code detected?

Current amperage in the rear heated oxygen sensor heater circuit has no activity.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– High Fuel Consumption
– Excessive Smoke from Exhaust

P0166 Description

The rear heated oxygen sensor (or sensor 3 for some vehicles), after three way catalyst (manifold), monitors the oxygen level in the exhaust gas on each bank. Even if switching characteristics of the heated oxygen sensor 1 are shifted, the air-fuel ratio is controlled to stoichiometric, by the signal from the heated oxygen sensor 3. This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. Under normal conditions the heated oxygen sensor 3 is not used for engine control operation.

P0166 Information for specific makes

P0166 HONDA