P0038: HO2S Heater Control Circuit High (Bank 1, Sensor 2) (Meaning, Causes, Fixes)
What P0038 means
Bank 1 Sensor 2 is the second oxygen sensor back on the side of the engine with cylinder #1 (an inline engine has only Bank 1), normally mounted after the catalytic converter. OBD-Codes.com explains that the engine computer (PCM) uses this sensor mainly to monitor how well the catalytic converter is working. Most modern oxygen sensors have four wires, two for the sensor itself and two for a built-in electric heater that brings it up to operating temperature quickly. The PCM controls when the heater is on and keeps watching the heater circuit for abnormal voltage, and on some vehicles abnormal current. According to OBD-Codes.com, vehicles control that heater one of two ways: either the PCM switches the 12-volt feed (directly or through an oxygen sensor relay) and the heater is grounded to the vehicle, or a fused 12-volt feed is always live with the key on and the PCM switches the ground side. If the PCM detects an abnormally high voltage on the heater circuit, P0038 may set. The code refers only to the heater half of the sensor. RepairPal describes it more simply: the PCM sets P0038 when it detects the heater wire is not operating. Nissan's wording, per OBD-Codes.com, is 'Heated oxygen sensor 2 Bank 1, heater voltage high'. P0141 is the general heater circuit code for this same sensor, P0037 is the circuit-low version, and P0032 is the same fault on the front (Sensor 1) sensor.
Severity: can I keep driving?
Drive with caution, fix soon
Usually drivable. RepairPal rates P0038 Moderate: not an immediate safety threat, but get it diagnosed within a reasonable time. OBD-Codes.com says there will likely be no symptoms other than the check engine light, but a car with an active check engine light will likely fail an OBD2 emissions inspection.
Common symptoms
- Check engine light on; OBD-Codes.com says there will likely be no other symptoms
- Decreased engine performance (RepairPal)
- Increased fuel consumption (RepairPal)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Faulty Bank 1 Sensor 2 oxygen sensor (both sources; RepairPal calls it oxygen sensor failure)
- Open in the heater control circuit, on systems where the PCM switches the 12-volt feed (OBD-Codes.com)
- Heater control circuit shorted to battery voltage, on systems where the PCM switches the 12-volt feed (OBD-Codes.com)
- Open heater ground circuit, on systems where the PCM switches the 12-volt feed (OBD-Codes.com)
- Heater control circuit shorted to ground, on systems where the PCM switches the ground side (OBD-Codes.com)
- Wiring issue (RepairPal) or a failed engine computer (PCM) (RepairPal lists PCM failure; OBD-Codes.com does not)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Read all stored codes. If P0038 shows up alongside other heater codes such as P0032 or P0141, look for a shared wiring or power problem before replacing several sensors.
- Visually inspect the Bank 1 Sensor 2 sensor (after the catalytic converter, cylinder #1 side) and its wiring harness. OBD-Codes.com says to look especially for bare wires where the wiring enters the sensor, since they can fatigue and short, and to make sure the wiring is routed away from the exhaust.
- Unplug the sensor and, with the key on and engine off, check for 12 volts at the heater feed in the harness connector, or for ground, depending on how your system is wired (OBD-Codes.com).
- Check that the heater control (ground) circuit is intact.
- Remove the sensor, inspect it for damage, and if you have the resistance specification, measure the heater element with an ohmmeter. Infinite resistance means the heater is open and the sensor needs replacing (OBD-Codes.com).
Typical fixes
- Replace the Bank 1 Sensor 2 oxygen sensor; RepairPal lists this as the common repair
- Repair wiring that is open, shorted, chafed where it enters the sensor, or melted by the exhaust, and reroute it away from hot parts
- Repair an open heater ground
- Diagnose the engine computer only after the sensor and wiring test good
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- The code returns right after a new sensor is fitted, which points to wiring or the computer
- You need a wiring diagram to tell whether your vehicle switches the heater's 12-volt feed or its ground, since the likely causes differ between the two
- The sensor is seized in the exhaust pipe
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0038 the front or rear oxygen sensor?
The rear one. Sensor 2 is the second sensor back on Bank 1, normally after the catalytic converter. OBD-Codes.com says the computer uses it mainly to check catalytic converter efficiency, which is why a fault here usually doesn't change how the engine runs.
What's the difference between P0037 and P0038?
Both are about the heater in the Bank 1 Sensor 2 oxygen sensor. P0037 means the computer saw a low voltage on the heater control circuit and P0038 means it saw a high voltage. P0141 is the general heater circuit malfunction code for the same sensor.
Do the sources agree?
Mostly, but not entirely. OBD-Codes.com says there will likely be no symptoms other than the check engine light, while RepairPal lists decreased engine performance and increased fuel consumption. OBD-Codes.com blames the sensor and specific opens or shorts in the heater circuit, while RepairPal also lists PCM failure. Neither treats it as a safety problem, and RepairPal rates it Moderate.
Sources
Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.