P0038 code: O2 Sensor Heater Control Circuit High (Bank 1, Sensor 2)
P0038 means o2 Sensor Heater Control Circuit High (Bank 1, Sensor 2). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0038 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.
P0038 symptoms
- 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 P0038
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 →
How to fix P0038
Easy — basic tools, most owners can do this
- Think back to recent exhaust or sensor work
P0038 often shows up soon after something changed underneath: an aftermarket exhaust, a new sensor, or a universal sensor spliced in with crimp connectors. A part meant for another position can carry a different heater rating, and crimped joints under the car corrode and add resistance. If someone worked there recently, start where their hands were.
- Inspect splices and terminals for resistance
Look for corroded crimps, green copper showing under the insulation, or terminals that are dull and slack. Resistance in the heater path is a classic reason the engine computer reads the circuit as high. Cut out bad crimps and replace them with soldered, sealed joints rather than more crimps.
- Check heater resistance against this position's spec
Unplug Bank 1 Sensor 2 and measure across its heater pins with the exhaust cold. Upstream and downstream heaters on the same car don't always share a value, so look up the figure for the downstream position specifically. A reading well above it — or a part number that doesn't belong in this location — explains the code.
- Voltage-drop both sides of the circuit under load
With the heater running and the sensor connected, back-probe and measure the drop from the fuse to the sensor's feed terminal, then from the control terminal back to the module. A sound circuit loses only a few tenths of a volt each way; more pinpoints resistance that a plain continuity check would pass. Confirm too that the control wire isn't carrying voltage when the diagram says it shouldn't.
- Install the correct part and recheck
Replace the sensor with one listed for the Bank 1 downstream position, plugged in rather than spliced wherever possible. If a known-good sensor and clean wiring still set P0038, the heater driver inside the engine computer is next in line — a dealer-tool diagnosis, not a parts gamble.
DIY or shop? Downstream work like this suits home mechanics: the sensor is usually within reach from underneath, and the checks that catch most P0038s — a bad splice, a wrong part, a heater out of spec — need only a multimeter. Voltage-drop testing takes more care but no special equipment. Leave it to a shop if the high reading traces to a short to voltage deep in the main loom, or if everything outside the module tests clean.
Tools for the DIY steps: Multimeter with back-probe leads · Jack stands or ramps · Soldering iron and heat-shrink · Wire strippers · O2 sensor socket
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0038.
Start a case with P0038 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0038?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0038: common questions
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?
Not something a code can answer by itself. As for the code: it's a lower-urgency repair, 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 — and if the light starts flashing, stop driving.
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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0038 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0038 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.