Inside every heated oxygen sensor (HO2S) runs a heater wire that helps get the device up to operating temperature quickly. When the PCM detects a discrepancy between the desired and actual state of the heater control circuit of the post-catalyst HO2S on bank 1, it may trigger code P0038.
What Does the P0038 Code Mean?
Diagnostic trouble code (DTC) P0038 stands for “HO2S Heater Control Circuit High (Bank 1 Sensor 2).
Oxygen sensors evaluate the amount of oxygen in the exhaust gas and send their readings to the powertrain control module (PCM). This data guides the adjustments made to the engine’s operating parameters, such as air and fuel intake, to maximize its performance.
The oxygen sensors can only attain their full precision once they reach a certain temperature. Their reliance on heat poses a problem when you start up your car for the first time in a day. The oxygen content readings taken during the warm-up period won’t have the accuracy the PCM needs to set the best parameters for the engine.
Heated oxygen sensors resolve this issue with the help of heater wires that raise their temperature faster than the device can warm up alone. In an OBD-II-compliant vehicle, the heated oxygen sensor has two wires for the heater element and two more for the sensor itself. The oxygen sensor in pre-OBD vehicles often only contains one wire.
The PCM constantly looks for out-of-the-ordinary voltages or current draw in the heater circuits.
The oxygen sensor 2 unit sits on the same side as the engine’s cylinder 1. It measures the oxygen content of the exhaust gases after the catalytic converter cleans their emissions.
Note: The Society of Automotive Engineers (SAE) set the generic code P0038. But the code description may vary depending on the vehicle manufacturer. For example, you may find the definition “Heated oxygen sensor (HO2S) 2 Bank 1 – heater voltage high” in some Nissan cars.
What are the Possible Causes of the P0038 Code?
Several factors may cause the heater control circuit of the bank 1 downstream oxygen sensor to display excessively high voltage levels. These include:
- Bad or failing oxygen sensor
- Problems in the O2 sensor circuit, such as open or shorts
- Faulty PCM (rare)
What are the Common Symptoms of the P0038 Code?
The PCM keeps track of the catalytic converter’s operation by checking the readings from the post-catalyst oxygen sensors. While code P0038 won’t severely compromise your car, it may cause notable symptoms like:
- An illuminated check engine light
How to Diagnose the P0038 Code
Oxygen sensors lend themselves to fairly easy evaluation and testing. While most car owners should bring their vehicle to the auto shop, drivers with some DIY skills may be able to diagnose code P0038.
You can watch the following videos to get a better understanding of the P0038 diagnosis:
How to Fix the P0038 Code
In most cases, replacing the faulty oxygen sensor will eliminate the problem responsible for the P0038 code. The exact fix, however, will likely differ based on the make and/or model of the vehicle. A P0038 Dodge case, for example, may entail a different repair than those that have worked for a P0038 in a Chrysler.
Check the sensor and its wiring harness for visible signs of damage that can cause short circuits. Disconnect the oxygen sensor and ensure that the right amount of ground is present.
You can also inspect the heater control ground circuit for damage. Connect an ohmmeter to the heater element and run a resistance test.
As with any automotive repair task, we suggest that you consult a repair manual to guide you through the entire diagnosis and repair of the P0038 code.