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P0051 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P0154 is an OBD-II Code that refers to HO2S Heater Control Circuit Low (Bank 2 Sensor 1)


A P0051 code is caused by an ECM (Engine Control Module) receiving a signal that it detects low system voltage in the heater control circuit, referencing Bank 2 Sensor 1. The sensor heater is used to test the exhaust stream from a heated oxygen sensor. If the value being sent from the saturated oxygen sensor is outside of the correct range as dictated by the manufacturer, then a code is triggered.


Common causes for this code include:

  • Wiring that is frayed or has been broken.
  • Open or loose wiring.
  • Broken or failed ground connection.
  • The heater circuit fuse has been blown
  • Bank 2 Sensor 1 failure
  • Bad ECM


The symptoms of a P0051 code are:

  • The Check Engine Light comes on and stays on.
  • The engine will not start in some cases.
  • The engine may run poorly and the vehicle may have a reduced power output.
  • In other cases, there are no symptoms present at all beyond the Check Engine Light being illuminated.


To diagnose a P0051 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Examine all wiring and connectors for damage.
  3. Perform a Heated Oxygen Sensor (HO2S) test to see if the vehicle needs repair.
  4. Check for bank 2, sensor 1 voltage while it is heating up both before and after applying battery power.
  5. If there is no change in the voltage while the heater is on, then replace the HO2S and recheck operation.
  6. If no issue can be found with Bank 2, Sensor 1 or any related circuits, then the ECM may need replacing

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P0051 code:

  • Not checking for and clearing all related codes in the system when a P0051 code is discovered.
  • Replacing parts without verifying repair first. 
  • Not performing a test drive after repairs to see if the vehicle returns to normal operation.
  • Not testing for Bank 2 Sensor 1 voltage before and after battery power is applied during a heating test.

How serious is this?

The P0051 code is not likely to have a major impact on the performance of the vehicle. The Check Engine Light being illuminated may cause a reduction in fuel economy and drivability, but it is unlikely that there will be any other noticeable effects.

In some cases where the wiring has been damaged or broken, there could be further issues with other systems if repairs are not completed quickly. In these cases, having a P0051 message appear may provide an early warning for other potential system failures by triggering a check engine light before they would otherwise be visible or diagnosed by a technician.

What repairs can fix the code?

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The following are solutions that may fix this problem:

  • Replacing wiring that is damaged or broken
  • Replacing open or loose wiring
  • Replacing ground connections that are corroded or faulty
  • Replacing any fuse that has blown due to corrosion, shorts, or other causes
  • Replacing the Heated Oxygen Sensor (HO2S) for Bank 2, sensor 1 if it fails a test 
  • Replace the ECM if all other repairs have been completed and the issue still persists.

Related codes

A P0051 is related to and may be accompanied by the following codes:

P0050 – HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

P0107 – Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

P0108 – Manifold Absolute Pressure/Barometric Pressure Circuit High Input

P0111 – Intake Air Temperature Circuit Malfunction


In conclusion, the P0051 code is a generic trouble code that means the computer has detected an issue with a predetermined range of values for the Heated Oxygen Sensor (HO2S) voltage. In most cases, this code will have little to no impact on the operation or performance of the vehicle beyond triggering a check engine light being illuminated. If there are further symptoms present, such as reduced power output, drivability issues, slow starts, etc., then it is best to look towards those issues as the root cause and repair accordingly.