P0051 code definition

HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

What the P0051 code means

This code is set when the car’s computer, or Engine Control Module (ECM), detects low system voltage in the heater control circuit. Specifically, the code is referencing Bank 2 Sensor 1. The heater circuit in the heated oxygen sensor is for warming the sensor before the vehicle reaches operating temperature for an accurate reading. This code may be seen with P0052.

What causes the P0051 code?

  • Bank 2 Sensor 1 failure
  • Poor connection or disconnected connector
  • Open or short in the wiring
  • Blown heater circuit fuse
  • ECM failure

What are the symptoms of the P0051 code?

With the P0051 code, a car will still run and drive; in most cases, the illuminated Check Engine Light on the dashboard will be the only noticeable symptom. Poor fuel economy may be noticed, and the vehicle may run roughly.

How does a mechanic diagnose the P0051 code?

  • Uses a professional grade scan tool to check for all codes present (must be used to show live sensor data)

  • Observes and takes note of any freeze frame data that is associated with the code (to be used in test drive)

  • After P0051 is confirmed, clears the code and performs a test drive under the same circumstances shown in the freeze frame data

  • If the P0051 code returns, performs a visual inspection to check the integrity of the wiring and sensor

  • Scans with a tool used to monitor live data from Bank 2 Sensor 1 if the previous step is found to be okay

  • Checks and tests the ECM if the sensor checks out

Common mistakes when diagnosing the P0051 code

Though the sensor itself is generally the cause of P0051, using the proper tools and following the complete diagnostic procedure without skipping any steps is required as to avoid unneeded repairs. Monitoring the sensor data from the scan tool's live data stream is the only way to check for proper operation, and the sensor should not be replaced until it is tested.

How serious is the P0051 code?

P0051 has easily managed symptoms but like any other code, it should be repaired at the earliest convenience. In rare cases where the vehicle runs poorly and the fuel economy goes down, caution is advised when driving to avoid any issues.

What repairs can fix the P0051 code?

P0051 is generally a quick fix with a reasonable cost at any qualified mechanic.

Additional comments for consideration regarding the P0051 code

If a fuse is found to be blown in the heater control circuit, there is always a reason for it; generally a wiring short. The fuse must be replaced after wiring is repaired.

A professional level scan tool is required to precisely and quickly diagnose P0051. The professional scan tool allows us to view live data from the sensor, such as the voltage and resistance. In addition, this shows us changes in the sensor readings as they occur.

Need help with a P0051 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.

This article originally appeared on YourMechanic.com as P0051 OBD-II Trouble Code: HO2S Heater Control Circuit Low (Bank 2 Sensor 1) and was authored by Spencer Clayton.


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