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P0043 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.

Definition

P0043 is an OBD-II Code that means HO2S Heater Control Circuit Low on Bank 1 Sensor 3.

Meaning

A P0043 code is the result of the ECM (Engine Control Module) receiving a signal from the HO2S (Heated Oxygen Sensor) saying that the heater circuit for the HO2S on Bank 1 Sensor 3 is not working or open circuit. The ECM then sets a P0043 code to let the driver know there is a problem with the heated oxygen sensor on Bank 1 Sensor 3.

Causes

Common causes for this code include:

  • Intermittent open or short in the heater circuit.
  • Bad HO2S.
  • Open, grounded, or corroded wiring harness.
  • Faulty ECM.

It is also important to note that since the P0043 code indicates that there is a problem with the heated oxygen sensor on Bank 1 Sensor 3, other codes along with it may indicate other problems as well if they are present such as no signal from any of the sensors indicating engine knock during low RPM and load conditions.

Symptoms

Symptoms of P0043 can include any or all of the following:

Check Engine Light.

Unusual fuel consumption (more or less than normal).

MIL (Malfunction Indicator Lamp) on.

Poor performance, lack of power.

Failing staled emission tests.

During cold weather, P0043 can be one of the most challenging problems to track down because it might only occur during very specific circumstances like when the engine is first started and has not yet fully warmed up or when driving at highway speeds for extended periods. Then it might suddenly reappear out of the blue until finally returning permanently after being reproduced several times under different conditions then tracked down to a faulty component.

Diagnosis

To diagnose a P0043 DTC, the Check Engine Light must be first diagnosed as being present by checking the MIL or turning it on and off several times. If the MIL is not blinking when activated, there is no reason to proceed any further with diagnostics because this will only result in verifying that a P0043 code has been set.

P0043 can be difficult to track down if intermittent, but a good place to start is by checking for proper voltage at both terminals of Bank 1 Sensor 3 during normal operation and during the warm-up condition (engine fully warmed up but still cold outside air temperature). In some cases, all one needs to do is pull both terminals off of the HO2S and clean them up for good contact with dielectric grease.

Another important thing to check is for proper ground or earth at the HO2S harness connector and the engine wiring harness. If ground is not present, it may indicate a bad HO2S, open in its ground circuit, shorted to power somewhere along the line, or an ECM problem.

Common mistakes

The following are common mistakes when diagnosing the trouble code P0043:

Failing to check the MIL first.

Not verifying that the code is being set.

Diagnosing the HO2S or wiring harness before checking for proper voltage at both terminals of Bank 1 Sensor 3 during normal operation and during the warm-up condition (engine fully warmed up but still cold outside air temperature).

Not checking for proper ground or earth at the HO2S harness connector and the engine wiring harness if other possible causes are eliminated.

How serious is this?

A car with a P0043 trouble code is a car that is not ready for emission testing. That does not necessarily mean it will fail an emission test, but any car with a P0043 trouble code should be properly diagnosed and repaired as soon as possible before going on a road trip or attempting to pass any emission tests. Otherwise, the driver may find out at the last minute when it counts that there is something seriously wrong under the hood such as excessive unburnt fuel in exhaust causing high hydrocarbon readings. HO2S Sensor heater failure can cause high HC and NOx levels, excessively lean fuel mixture due to defective components leading to catalytic converter damage and/or excess oxygen sensor activity resulting in misfiring and/or rough running engine.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Replacing the HO2S.
  • Updating the ECM to newer software.
  • Checking the grounds and power circuits at both sensor terminals for corrosion or damage.
  • Repairing open ground circuit.
  • Cleaning up terminal connections for proper contact with dielectric grease if necessary.

Related codes

P0051 - HO2S Sensor Heater Circuit High Voltage Bank 1 Sensor 2

P0053 - HO2S Sensor Heater Circuit Low Voltage Bank 1 Sensor 2

P0107 - Mass air flow circuit range/performance fault

P0108 - Mass airflow sensor upstream hose off or plugged

P0044 - HO2S Sensor Heater Circuit Low Voltage Bank 2 Sensor 1

P0046 - HO2S Sensor Heater Circuit High Voltage Bank 2 Sensor 1

P0141 - HO2S Sensor Heater Circuit Low Voltage (Camry & ES 350)

How much does it cost to fix the P0043 code?

Repairs for this code typically cost between $200 and $350. This does not include diagnostics which can cost around $100 in some areas. If the diagnosis shows that there is an HO2S problem instead of a sensor heater problem, then it is quite possible that charging an additional $650 to replace the downstream heated oxygen sensor (HO2S) may fix this code as well.

Conclusion

In conclusion, the P0043 is a trouble code that will be set if there is a malfunction with the HO2S Sensor heater circuit. The HO2S Sensor heater circuit provides the heating voltage to the downstream oxygen sensor. By providing an operating voltage, it increases sensor sensitivity allowing for more accurate readings by the ECM. Without this circuit working correctly, the downstream oxygen sensor will not work properly causing high emissions and poor fuel economy. Replacing or repairing any part of this circuit will fix this code for good.

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