Technical Description of OBD-II Trouble Code
Generic: The control circuit for the oxygen (A/F) sensor heater is experiencing low voltage on Bank 2 Sensor 1.
Nissan: The voltage for the heated oxygen sensor (HO2S) 1 on Bank 2 is low.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles, including Toyota, VW, Ford, Dodge, Honda, Chevrolet, Hyundai, Audi, Nissan, and others. The specific repair steps may vary depending on the model.
A P0051 DTC trouble code refers to the O2 sensor (oxygen sensor) located on Bank 2 in front of the catalytic converter. There is also an oxygen sensor behind the converter, which is Sensor #2. Bank #2 refers to the side of the engine that does not contain cylinder #1.
This O2 sensor #1 may also be referred to as an air/fuel ratio sensor on some vehicles. It detects the amount of oxygen in the exhaust gas compared to the outside air, and the vehicle’s computer adjusts the air/fuel ratio going into the engine. The sensor is less effective when the exhaust gas temperature is low, so it includes a heater that is activated to help obtain better readings from the A/F O2 sensor. Essentially, this P0051 code means that the resistance of the heater circuit is lower than normal. In most cases, the resistance level must fall below 0.8 A to trigger the DTC code.
Note that this code is very similar in nature to P0031, P0032, and P0052.
Potential Symptoms
Most likely, you will not notice any symptoms other than the MIL (malfunction indicator lamp, a.k.a. the check engine light) illuminating.
Causes
A P0051 DTC trouble code may be caused by one or more of the following:
Possible Solutions
To resolve a P0051 DTC code, a proper diagnosis is required. Inspect the wiring and connectors leading to the sensor. If equipped with a heater relay and fuse, check those as well. Use a digital volt ohm meter to:
Refer to a 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, a common fix for this DTC is to replace the air/fuel (O2 oxygen) sensor #1 on bank 2 (the side of the engine that doesn’t contain cylinder #1).
Please keep in mind that OEM (original equipment) replacement sensors are recommended (from the dealer). Aftermarket sensors can be less reliable and of poorer quality (not always, but more often). There’s also a chance that replacement parts for the P0051 code may also fall under a federal emissions warranty (check with your dealer to see if it’s covered).
