P0038: O2 Sensor Heater Control Circuit High (Bank 1 Sensor 2)
P0038 means the engine computer detected too high a voltage in the heater circuit of the downstream oxygen sensor (the one behind the catalytic converter) on bank 1. It usually does not affect how the car drives, but it turns on the check engine light and can cause an emissions test failure.
You can keep driving
The reference lists no limp mode for this code and usually no noticeable drivability problem, so short-term driving is generally fine. Get it fixed soon, because the catalyst monitor cannot complete and an emissions test or readiness check can fail. A wiring short can also get worse over time.
What it means
The oxygen sensor behind the catalytic converter (the exhaust part that cleans harmful gases) mainly checks whether the converter is working. It has a built-in heating element so it reaches working temperature quickly. The heater gets battery voltage through a fuse, and the engine control module switches the ground side on and off with a pulsed signal while checking that the circuit matches what it commanded. P0038 sets when the module sees too high a voltage in that control circuit, typically because the switched ground wire is shorted to battery voltage. Each manufacturer defines which physical fault triggers the general, low or high version of this code. Without proper heating, the sensor becomes ready late and the catalyst monitor may not complete. Bank 1 is the side of the engine that contains cylinder number 1.
Likely causes
- Heater control wire shorted to battery voltage (for example a chafed harness)Very likely
Damaged insulation lets the switched ground wire touch a battery-voltage source, which produces exactly the high-voltage reading this code describes.
- Heating element shorted internallyPossible
A fault inside the sensor's heater can upset the circuit voltage the module sees, so the sensor itself may need replacing.
- Water in the connectorPossible
Moisture can cause leakage between connector pins and change the voltage in the heater circuit.
- Output driver or software of the engine control moduleLess likely
The module's internal switching circuit or programming can fail, but this is much less common than a wiring or sensor fault.
What you may notice
- Check engine light on
- Usually no noticeable drivability problem
- Catalyst monitor does not complete
- Emissions test or readiness check failed
What to check, cheapest first
- 1Read the code with a scanner and note any related codes such as P0036, P0037, P0058, P0054 or P0141, then clear it and see if it returns. · you can do it
- 2Look at the wiring harness to the bank 1 downstream oxygen sensor for chafed, melted or pinched insulation, especially near the exhaust. · you can do it
- 3Unplug the sensor connector and check for water, corrosion or bent pins between the terminals; dry and clean it if needed. · you can do it
- 4Measure the sensor heater element resistance and compare it with the manufacturer's specification to see if the element is shorted. · mechanic
- 5Check the heater control wire for a short to battery voltage between the sensor connector and the engine control module. · mechanic
- 6If wiring and sensor test fine, test the module's output driver and check for software updates. · mechanic
Related codes
Frequently asked questions
Can I keep driving with a P0038 code?+
Usually yes, since there is typically no noticeable drivability problem. Repair it soon so the catalyst monitor can complete and the wiring fault does not spread.
Can a loose gas cap cause P0038?+
No. This code points to the electrical circuit of the oxygen sensor heater, not the fuel system or evaporative system.
Will P0038 pass an emissions test?+
Probably not. The check engine light is on and the catalyst monitor may not complete, so the test or readiness check can fail.
Can I fix it myself?+
Often yes. The repair is rated medium difficulty and can be done at home, with an estimated 0.3 to 1.5 hours. After the repair, a drive cycle is needed for the monitors to complete.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10