P0043 HO2S Heater Control Circuit Low (Bank 1 Sensor 3)

Technical Description of OBD-II Trouble Code

The control circuit for the HO2S heater is operating at a low level (Bank 1 Sensor 3).

What does that signify?

This diagnostic trouble code (DTC) is a standard powertrain code that is applicable to vehicles equipped with OBD-II, including Nissan, Toyota, Mazda, Mitsubishi, Lexus, Infiniti, VW, and others. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.

Heated Oxygen sensors (HO2S) are used by the PCM (Powertrain Control Module) to determine the oxygen content in the exhaust system. Bank 1, sensor 3 refers to the third sensor located at the back of bank 1. Bank 1 is the side of the engine that contains the #1 cylinder (inline engines only have one bank). The PCM utilizes the information from the bank 1, sensor #3 HO2S primarily to monitor the efficiency of the catalytic converter. The sensor includes a heater element that is integral to its functioning.

The PCM controls the heater to warm up the sensor to its operating temperature. This enables the engine to enter closed loop faster and reduces emissions during cold startup. The PCM continuously monitors the heater circuits for abnormal voltages or, in some cases, abnormal amperages. Depending on the vehicle’s make, the Oxygen sensor heater is controlled in one of two ways. One way is that the PCM directly controls the voltage feed to the heater, either directly or through a HO2S relay, and a ground is supplied from the vehicle’s common ground. The other way is through a fused 12 volt Battery feed (B+) that supplies 12 volts to the heater element whenever the ignition is on, and the control of the heater is done by a driver in the PCM that controls the ground side of the heater circuit.

It is important to determine which type of control is present because the PCM activates the heater under various circumstances. If the PCM detects an abnormally low voltage condition on the heater circuit, it may trigger the P0043 code.

Symptoms

The symptoms of a P0043 DTC may include:

Causes

Potential causes of a P0043 trouble code may include:

Possible Solutions

Perform a visual inspection of the bank 1, sensor 3 HO2S and wiring harness. If there is any damage to the sensor or wiring, repair or replace them as necessary. Ensure that the wiring is routed away from the exhaust. If everything appears to be in order, unplug the Bank 1,3 HO2S and check for the presence of 12 volts B+ with the key on engine off (or the presence of ground, depending on the system).

Verify that the heater control (ground) circuit is intact. If it is, remove the O2 sensor and inspect it for damage. If you have access to resistance specifications, you can use an Ohmmeter to perform a resistance test of the heater element. Infinite resistance indicates an open in the heater. Replace the oxygen sensor as necessary.

Professional Service

While we always recommend resolving this issue through mechanical means, if that is not possible, we offer the option to permanently delete this specific DTC. We will continue to work on all other codes. If you are interested in this option, please upload your ECU file to our portal.