P0166 OBD-II Trouble Code: O2 Sensor Circuit No Activity Detected (Bank 2, Sensor 3)

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Cost of diagnosing the P0166 code

P0166 is a diagnostic trouble code (DTC) for "O2 Sensor Circuit No Activity Detected (Bank 2, Sensor 3)". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
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Check Engine Light

P0166 Code Definition

O2 Sensor Circuit No Activity Detected (Bank 2, Sensor 3)

What the P0166 code means

The P0166 code means that the third oxygen sensor on the second bank of the exhaust has failed or is not responsive.

The powertrain control module is not receiving a signal from this particular oxygen sensor. This may also be due to the sensor being unplugged.

What are the causes of the P0166 code?

  • An unplugged oxygen sensor
  • Faulty oxygen sensor
  • Damaged electrical connector or wiring associated with the oxygen sensor
  • Faulty powertrain control module

What are the symptoms of the P0166 code?

Symptoms that a driver may experience with a P0166 would include decreased fuel mileage, incorrect air/ ratio which may cause the engine to run incorrectly, and of course the Check Engine Light being illuminated.

How does a mechanic diagnose the P0166 code?

A mechanic may diagnose the P0166 code by using an OBD-II scanner to run data on the vehicle while the engine is running.

Assuming the scan tool has the capability, the signal voltages given from the oxygen sensors should be displayed while running data if the oxygen sensors are working correctly.

If no reading is given from any of the oxygen sensors, the sensor in question may be unplugged or faulty. The mechanic would then give the oxygen sensors a visual inspection to make sure that they are all plugged in.

If the sensors are all plugged in and none of the wiring has been damaged, then the mechanic may test the one in question for functionality with the manufacturer’s specific procedure. If all of these tests have been performed and the fault has not been found yet, the issue likely lies within the powertrain control module.

Common mistakes when diagnosing the P0166 code

A common mistake that may be made while diagnosing the P0166 code would be replacing the oxygen sensor without properly testing it. The manufacturer posts testing procedures for common faults for a reason.

Any code that can be stored in a vehicle’s powertrain control module likely has a diagnostic procedure provided by the manufacturer. It is best to follow these procedures to avoid misdiagnosis and save time and money.

How serious is the P0166 code?

This code is not very serious as long as it is not associated with any other trouble codes. Especially considering that this code is related to the third oxygen sensor on the second bank of the exhaust.

This means that the engine is likely a V-shaped engine that has at least six oxygen sensors. With the loss of one sensor, the powertrain control module should be able to maintain a correct air/fuel ratio with the inputs from all of the other sensors.

What repairs can fix the P0166 code?

Additional comments regarding the P0166 code

It is not a good idea to drive your vehicle for an extended period of time with a Check Engine Light. With this in mind it is a good idea to have this code diagnosed and repaired as soon as possible although this particular code is not as serious as some other trouble codes may be.

Need help with a P0166 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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P0166

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Patrick

30 years of experience
865 reviews
Patrick
30 years of experience
Patrick did a great job and pin point the problem quick , he will be my mechanic for now on ,
2003 FORD EXPEDITION - CHECK ENGINE LIGHT IS ON - DEL VALLE, TEXAS

Robert

28 years of experience
500 reviews
Robert
28 years of experience
Check Engine Light. Robert was able to diagnose it to be P0135: HO2S- Heater Circuit Conditions
1999 HONDA CIVIC - CHECK ENGINE LIGHT IS ON - FREMONT, CALIFORNIA

Edmar

19 years of experience
40 reviews
Edmar
19 years of experience
Edmar took the time to properly diagnose my issue and perform the proper checks to confirm the oxygen sensor code that was displayed from my car's electronic control module. (Check engine light came on.) I have already scheduled him to perform the repair now that we know the issue and know what parts are needed.
2004 TOYOTA HIGHLANDER - CHECK ENGINE LIGHT IS ON - FRISCO, TEXAS

Scott

31 years of experience
30 reviews
Scott
31 years of experience
Very nice friendly mechanic. Very helpful with with questions that I had. Offered good advice. He explained some of the problems to me and what should be the next to resolve it before spending unnecessary monies. This was my first time using him and will not be my last. I would recommend him to anyone. Especially women because he does not seem to take advantage of our knowledge of not knowing things about cars.
2001 HYUNDAI ELANTRA - CHECK ENGINE LIGHT IS ON - PARKVILLE, MARYLAND

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