Fault code P0051 is called “HO2S Heater Oxygen Sensor Control Circuit Low (Bank 2, Sensor 1)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0051
This Diagnostic Trouble Code (DTC) is a generic powertrain code. Error P0051 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.
Heated oxygen sensors (HO₂S) are used in vehicles to determine the oxygen content in the exhaust system before and after the catalytic converters. They use feedback to adjust the fuel system. To maintain an optimal air/fuel mixture ratio of 14.7:1.
Oxygen sensors use a heated sensor circuit for faster feedback to the control module. The oxygen sensor can use three or four wires depending on the vehicle.
Two are typically used for feedback to the transmission control module (PCM). And the other wires are for the heater and to power the heated circuit. Three-wire sensors are usually grounded through the exhaust system. And four-wire sensors have a separate ground wire.
Code P0051 refers to the sensor in front of the Bank 2 catalytic converter, which is on the opposite side of the engine from cylinder 1. The error means that the problem with the HO₂S sensor heater element has not been corrected. This code is triggered when a low signal level is detected in the oxygen sensor heating circuit.
Symptoms of vehicle malfunctions
The main signal that an error P0051 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The Check Engine light on the control panel will illuminate (the code will be written to the ECM memory as a fault).
- In some cases, the engine control module (ECM) may put the vehicle into emergency operation.
- Sometimes there may be no symptoms despite the stored fault code.
If fault code P0051 appears, the vehicle can continue to drive, but the problem must be corrected as soon as possible. To prevent potential problems such as sensor circuit failure and increased fuel consumption. If the problem is ignored for a long time, unstable engine operation may occur, and other components may be damaged.
Factors that can cause this error code
The error code P0051 can mean that one or more of the following problems have occurred:
- Open circuit of power supply, grounding or heater circuit of sensor O₂.
- Defective sensor heater O₂.
- Damaged or worn connectors to the sensor.
- Sometimes a faulty PCM module is the cause.
Low circuit input codes are often the result of low battery voltage. Also bad connections between electrical connectors or previously repaired wiring. Corrosion of electrical connectors is also possible.
How to fix or reset OBD-2 code P0051
Some suggested steps for troubleshooting and fix the error code P0051:
- Clear the error codes from the vehicle’s computer memory.
- Test drive the vehicle to see if code P0051 appears again.
- Perform a visual inspection and repair or replace damaged electrical wiring if necessary.
- Check the grounding, and correct the problem if necessary.
- If there is a problem with the PCM, reprogram or replace the engine control module.
Diagnose and repair of problems
Failure P0051 can only be caused by the oxygen sensor heater circuit or by the sensor itself. Diagnostics usually begins with checking the sensor wiring. Usually the heated oxygen sensor comes with four wires.
Two wires go directly to the heater circuit, and the other two are for powering and grounding the sensor. You may need a wiring diagram of your car. To be sure you’re checking the right set of wires.
Wiring check
Check the heater circuit with a digital multimeter or voltmeter. Refer to the vehicle’s wiring diagram to determine the exact pins of the connector where the ground is installed.
The reading should be close to the battery voltage. If it is not, there is most likely a problem with the sensor power.
It is also necessary to check the ground. To do this, connect the positive battery terminal to the red wire on the multimeter. And the black wire to the ground to check the circuit ground. The result should be 12 V, if not, it indicates a grounding problem on the sensor.
Check the sensor
If power and ground are okay, the next option is to check the sensor heating element. To determine if it has an open circuit or high resistance.
Set a voltmeter on the ohm scale, check the resistance of the heater circuit, using the wiring diagram as a reference.
Make sure that you have disconnected the oxygen sensor O₂. The heater circuit inside the sensor should have a low resistance. Exceeding the limit value indicates a break in the heater part. Therefore, the oxygen sensor will have to be replaced.
On which vehicles does this problem occur most frequently
Fault code P0051 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Audi
- BMW
- Chevrolet
- Chrysler (Voyager)
- Dodge
- Ford (Focus)
- Honda
- Hyundai (Santa Fe)
- Infiniti (FX35, G35, G37)
- Jeep (Grand Cherokee, Wrangler)
- Lexus (ES350, GS300, GX470, IS250, LX570, RX350)
- Mazda (MPV)
- Mitsubishi (Eclipse)
- Nissan (Maxima, Murano, Patrol, Teana)
- Subaru (Legacy, Outback, Tribeca)
- Suzuki (Grand Vitara)
- Toyota (Avensis, Camry, Crown, Land Cruiser, Prado)
- Volkswagen
Fault code P0051 can sometimes be found with other errors. The most common are the following: P0031, P0032, P0037, P0052, P0057, P0123, P0141, P0152, P0155, P0161, P0356, P0404, P0753, P1598, P2197, C1201.
