Technical Description of OBD-II Trouble Code
The control circuit for the heater of the HO2S is registering a high voltage (Bank 1 Sensor 3)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II, including Nissan, Mitsubishi, Mazda, Subaru, Toyota, VW, and others. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Engines today commonly have oxygen sensors with a heating element. Heated oxygen sensors (HO2S) are inputs used by the PCM (Powertrain Control Module) to determine the oxygen content in the exhaust system.
The PCM primarily uses the information obtained from the HO2S of Bank 1, Sensor #3 to monitor the efficiency of the catalytic converter. This sensor contains a heater element. In older vehicles without OBD-II, an oxygen sensor was a one-wire sensor, but now they are typically four-wire sensors: two wires dedicated to the oxygen sensor and two wires dedicated to the heater element. The oxygen sensor heater helps to achieve closed loop more quickly. The PCM controls the duration of the heater operation. The PCM also 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. (1) The PCM directly controls the voltage supply to the heater, either directly or through a HO2S relay, and a ground is provided from the vehicle’s common ground. (2) There is 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 managed by a driver in the PCM that controls the ground side of the heater circuit. It is important to determine which type is present because the PCM activates the heater under various circumstances.
If the PCM detects an abnormally high voltage condition in the heater circuit, it may trigger the P0044 code. This code specifically refers to the heating circuitry portion of the oxygen sensor.
Symptoms
Possible symptoms of a P0044 DTC may include:
There are unlikely to be any other symptoms.
Causes
Potential causes of a P0044 code include:
Possible Solutions
First, visually inspect the third HO2S oxygen sensor downstream from the engine on bank 1 and its wiring harness. If there is any damage to the sensor or wiring, repair it as necessary. Check for bare wires where the wiring enters the sensor, as this can cause fatigue and shorts. Ensure that the wiring is routed away from the exhaust. Repair the wiring or replace the sensor as needed.
If everything appears to be in order, unplug the #3 bank 1 HO2S and verify that there is 12 volts B+ present with the key on and the engine off (or that ground is present, depending on the system). Confirm that the heater control (ground) circuit is intact. If so, 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 on the heater element. Infinite resistance indicates an open in the heater. Replace the oxygen sensor as necessary.
