P0051 - Oxygen Sensor (A/F) Heater Control Circuit Low (Bank 2 Sensor 1)
OBD2 Error Codes

P0051 - Oxygen Sensor (A/F) Heater Control Circuit Low (Bank 2 Sensor 1)

P0051 - Oxygen Sensor (A/F) Heater Control Circuit Low (Bank 2 Sensor 1)

OBD-II DTC Datasheet

Common: Oxygen Sensor (A/F) Heater Control Circuit Low (Bank 2 Sensor 1) Nissan Heated Oxygen Sensor (HO2S) 1 Bank 2 - Heater Voltage Low

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles including but not limited to Toyota, VW, Ford, Dodge, Honda, Chevrolet, Hyundai, Audi, Nissan, etc. E. Specific repair steps may vary depending on the model.

The P0051 DTC is related to the O2 sensor (oxygen sensor) located on the bank 2 before the catalytic converter. Behind the transducer is also an oxygen sensor, which is the #2 sensor. Bank #2 is the side of the engine that does not contain cylinder #1.

This # 2 O1 sensor may also be referred to as an air / fuel ratio sensor as it is on some vehicles. It detects the amount of oxygen in the exhaust compared to outside air, and then the car's computer adjusts the air / fuel ratio to the engine. The sensor is less effective at low exhaust temperatures, so it turns on a heater that activates to help get the best reading from the A / F O2 sensor. Basically, this P0051 code means that the resistance of the heater circuit is below normal. In most cases, this resistance level must fall below 0.8 A for the DTC to set.

Please note that this code is very similar in nature to P0031, P0032, and P0052.

Possible symptoms

Most likely you will not notice any symptoms other than the malfunction indicator lamp (check engine lamp) comes on.


The P0051 DTC can be caused by one or more of the following:

  • Short circuit in the heater circuit in the sensor
  • Defective O2 sensor heater
  • Broken / worn wiring / connectors to sensor and / or relay
  • Defective PCM / ECM

Possible solutions

To fix the P0051 DTC, you need to run proper diagnostics. To do this, you need to inspect the wiring and connectors leading to the sensor. Also, if you have a heater relay and fuse, you will want to test them as well. Use a digital volt-ohmmeter to:

  • check for 12 volts on the heater circuit power (hint: disconnect the sensor and check the wiring connector to take this measurement)
  • check the ground circuit for continuity
  • measure the resistance of the heater circuit (done on the sensor itself)
  • measure the resistance and voltage of the wiring

Refer to your service manual for the correct specifications (volts, ohms) for your vehicle. On some Toyota vehicles, this code is triggered when the resistance of the heater circuit is below 0.8 A.

With that said, the usual solution for this DTC is to replace the No. 2 Air/Fuel (Oxygen O1) sensor on Bank 2 (the side of the engine that does not contain cylinder No. 1).

Note that replacement of OEM sensors (original equipment) is recommended (by dealer). Aftermarket sensors may be less reliable and of lower quality (not always, but more often). There is also the possibility that parts code P0051 may also be eligible for a federal emissions guarantee (check with your dealer if this applies).

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