OBD codes / P0038
P0038
ModerateO2 Sensor Heater Control Circuit High (Bank 1, Sensor 2)
P0038 won't change how the car behaves — it's an electrical fault in a monitoring sensor's heater, downstream of the converter. Drive normally and book the repair when convenient; the one hard deadline is any upcoming emissions inspection, which the active code will fail.
What this code means
This code lives in the heater circuit of the downstream oxygen sensor — Bank 1, Sensor 2, positioned after the catalytic converter on the side of the engine where cylinder 1 sits. The heater's purpose is simple: warm the sensor to operating temperature within seconds of start-up so the computer can begin verifying converter performance early. P0038 means the control circuit voltage read higher than expected — the signature of a short to battery voltage in the wiring, or excessive resistance from corroded connector pins or a deteriorating heater element. It is worth stressing that this is an electrical fault at the sensor, not a statement about the converter itself. Real-world causes rank roughly: aging sensor heater, damaged or corroded underbody wiring and connectors, and rarely a fault in the computer's heater driver. Meanwhile the car drives normally; the sensor still reads once exhaust heat warms it, just later than designed.
Symptoms you might notice
- Check-engine light with otherwise normal driving
- No perceptible performance or economy change
- Emissions inspection failure while the code is present
What it costs to fix
Typical range: $125–$400 · about ~0.3–1.2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Downstream oxygen (O2) sensor | $30–$200 | ~0.3–1.2 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
| Heater-circuit fuse | $1–$10 | ~0.1–0.3 hrs |
Usually a modest repair: the downstream sensor is on the cheaper end of O2 sensors, and labor hinges mostly on access under the vehicle. Corroded connectors — common where roads are salted — can sometimes be fixed for the cost of terminal cleaner and a repair pigtail.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0038 for my exact vehicle →
Frequently asked
Does P0038 mean my catalytic converter is bad?
No. P0038 is purely about the heater circuit in the sensor that watches the converter — it says nothing about the converter itself. A genuinely failing converter sets efficiency codes like P0420, not heater codes.
What does the 'high' in P0038 indicate?
That the heater control circuit showed more voltage than the computer expected — commonly a wire shorted to battery voltage, or resistance built up in corroded terminals or an aging heater element. It's the opposite finding from the 'low' code P0037.
Is it OK to drive with P0038 for a few weeks?
Yes. Fuel control, power, and reliability are unaffected because the downstream sensor doesn't steer the mixture. Just remember an illuminated check-engine light can conceal newer faults, so don't let 'a few weeks' turn into a year.
What will fixing P0038 cost?
Typically in the low hundreds if the sensor needs replacing, with the part often cheaper than an upstream sensor. If the culprit turns out to be a corroded connector or damaged wire, the fix can cost well under a hundred dollars.
Seeing P0038 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0038 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.