P0038 is an OBD-II trouble code that points to a problem with the heater circuit in an oxygen sensor, usually on Bank 1 Sensor 2. When this code sets, your ECU has detected higher than expected voltage in the heater control circuit, which often means a wiring issue, short to power, or a failed sensor. You might notice a check engine light, poor fuel economy, or no symptoms at all. Understanding what P0038 means, how it affects your vehicle, and how to diagnose it will help you decide whether you can handle it yourself or need a shop.
What Does P0038 Mean?
P0038 stands for “HO2S Heater Control Circuit High (Bank 1 Sensor 2).” In plain terms, your ECU has found that the heater circuit for the downstream oxygen sensor on Bank 1 is seeing too much voltage or current.
The heater in the O2 sensor helps it reach operating temperature quickly so the ECU can control fuel mixture and monitor the catalytic converter. When the circuit is “high,” the ECU sees a signal outside its normal range, often due to a shorted wire, damaged connector, or internally shorted sensor heater.
Quick Reference
- Code: P0038
- Meaning: HO2S Heater Control Circuit High (Bank 1 Sensor 2)
- Typical culprit: Failed downstream O2 sensor or wiring short
- Urgency: Moderate – usually safe to drive short term
- Common symptoms: Check engine light, possible poor fuel economy
Real-World Example / Field Notes
In the shop, I see P0038 most often on higher-mileage vehicles where the downstream O2 sensor has been cooked by years of exhaust heat. A typical case: a mid-2000s SUV comes in with only a check engine light and no drivability complaints. Scan shows P0038, freeze-frame data points to a cold start event, and a quick check with a multimeter reveals the heater circuit is shorted to power inside the sensor. Replacing the Bank 1 Sensor 2 O2 sensor and clearing the code fixes it, and the customer is back on the road in under an hour.
Symptoms of P0038
- Check engine light on: The most common and sometimes only symptom.
- Reduced fuel economy: ECU may run a slightly richer mixture if monitoring is affected.
- Failed emissions test: Readiness monitors may not set, or tailpipe emissions may be high.
- Rough idle (occasionally): Some vehicles react poorly to O2 sensor heater faults.
- Delayed closed-loop operation: Engine may stay in open loop longer on cold starts.
- Stored catalyst efficiency codes: In some cases, catalyst monitoring is impacted.
- Increased exhaust smell: Slight raw fuel smell from richer mixture on some engines.
Common Causes of P0038
Most Common Causes
- Failed downstream oxygen sensor (Bank 1 Sensor 2) heater element shorted internally.
- Short to battery voltage in the O2 sensor heater power or control wire.
- Damaged or melted wiring harness near the exhaust or catalytic converter.
- Corroded or water-intruded connector causing abnormal voltage readings.
Less Common Causes
- Incorrect or low-quality aftermarket O2 sensor with wrong heater resistance.
- Blown or incorrect fuse feeding the O2 heater circuit (depending on design).
- Faulty relay controlling the O2 sensor heater power supply.
- ECU (PCM) output driver fault for the O2 heater control circuit.
- Previous wiring repairs done poorly (twist-and-tape splices, wrong gauge wire).
Diagnosis: Step-by-Step Guide
You will want a basic scan tool, a digital multimeter, and ideally a wiring diagram for your vehicle. A capable scanner that can read live data and Mode $06 can make this easier, but you can still do a lot with a simple code reader and meter.
- Confirm the code and check for companions. Scan the ECU and note any other O2 or heater-related codes (P0030–P0064 range, P0420, etc.). Multiple codes can point to a shared fuse or power issue.
- Inspect the sensor location. Identify Bank 1 Sensor 2 – this is the downstream sensor on the side of the engine with cylinder #1, after the catalytic converter. Visually inspect the sensor body, wiring, and connector for burns, melted insulation, or physical damage.
- Check the harness routing. Follow the O2 sensor harness as far as you can. Look for spots where it may have rubbed on the exhaust, frame, or suspension, or where zip ties or clips have broken and let it sag onto hot components.
- Test heater circuit power and ground. With key ON (engine off), back-probe the heater power wire at the connector using a wiring diagram for reference. You should see battery voltage on the power feed. Verify the ground or control side is not stuck at full battery voltage when it should be controlled by the ECU.
- Measure heater resistance. With the sensor unplugged and engine off, use your multimeter to measure resistance across the heater pins on the sensor side. A typical value is usually between 3–20 ohms (check specs). A reading near 0 ohms suggests a short; infinite resistance indicates an open heater.
- Check for short to power. With the sensor unplugged, check the heater control wire (ECU side) to battery positive for continuity. Any continuity or voltage where there should be none can indicate a shorted wire or ECU driver issue.
- Inspect fuses and relays. Locate the fuse and any relay that supply the O2 heater circuit. Verify the correct fuse rating, check for blown fuses, and test or swap relays if necessary.
- Use live data if available. On some scan tools, you can monitor O2 heater status or current draw. Check that the ECU is commanding the heater on during cold start and that the downstream O2 sensor warms up and responds normally.
- Substitute with a known-good sensor if needed. If wiring, fuses, and power/ground check out, replacing the Bank 1 Sensor 2 O2 sensor is often the next logical step.
Pro tip: Always disconnect the battery or pull the appropriate fuse before doing any major wiring repairs near the exhaust. This helps protect the ECU from accidental shorts while you’re probing or soldering.
Possible Fixes & Repair Costs
Most P0038 repairs involve replacing the downstream O2 sensor on Bank 1 or repairing damaged wiring. A quality oxygen sensor typically costs $60–$200 for parts, with labor ranging from 0.5–1.5 hours depending on access, so you might see $150–$350 at a typical shop. Wiring repairs can vary widely: a simple connector fix might be under $100, while extensive harness repair can exceed $300. If an ECU or relay is at fault, costs climb, but that’s far less common. Location, vehicle make, and shop labor rate all affect the final bill.
Can I Still Drive With P0038?
In most cases, you can still drive with a P0038 code without immediate danger to the engine. The heater circuit issue typically affects how quickly the O2 sensor reaches operating temperature rather than basic engine operation. However, you may see reduced fuel economy, and your vehicle may fail an emissions test. Long-term driving with this code active is not ideal because it can mask other issues and may eventually contribute to catalytic converter stress if the mixture stays richer than intended.
What Happens If You Ignore P0038?
If you ignore P0038, you risk running with less precise fuel control, especially during warm-up, which can increase fuel consumption and emissions. Over time, excessive rich operation can overheat and damage the catalytic converter, turning a relatively simple sensor or wiring repair into a very expensive exhaust system replacement.
Related Codes
- P0027 – Exhaust Valve Control Solenoid Circuit Range/Performance Bank 1
- P0026 – Intake Valve Control Solenoid Circuit Range/Performance Bank 1
- P0019 – Crankshaft Position Camshaft Position Correlation Bank 2 Sensor B
- P0018 – Crankshaft Position Camshaft Position Correlation Bank 2 Sensor A
- P0017 – Crankshaft Position Camshaft Position Correlation Bank 1 Sensor B
- P0016 – Crankshaft Position Camshaft Position Correlation Bank 1 Sensor A
- P0009 – Engine Position System Performance Bank 2
- P0008 – Engine Position System Performance Bank 1
- P0007 – Fuel Shutoff Valve “A” Control Circuit High
- P0006 – Fuel Shutoff Valve “A” Control Circuit Low
Key Takeaways
- P0038 indicates a high-voltage issue in the heater circuit for the Bank 1 Sensor 2 oxygen sensor.
- The most common causes are a failed O2 sensor heater or wiring short near the exhaust.
- You can usually drive short term, but fuel economy and emissions can suffer.
- Basic tools and a careful visual inspection often pinpoint the problem quickly.
- Typical repair costs range from about $150–$350 for sensor replacement at a shop.
Vehicles Commonly Affected by P0038
P0038 can appear on almost any OBD-II vehicle, but in the bay I see it frequently on popular models from Toyota, Lexus, Honda, Acura, Nissan, Infiniti, Ford, Chevrolet, GMC, Dodge, Jeep, Subaru, Hyundai, and Kia. It’s especially common on V6 and V8 engines where exhaust heat and tight packaging can cook downstream sensors and wiring. High-mileage SUVs, trucks, and crossovers often show this code as original O2 sensors age and harness clips break, letting the wiring sag onto hot exhaust components.
FAQ
Can P0038 cause engine damage?
P0038 by itself usually does not cause immediate engine damage. However, if it leads to a consistently rich mixture over time, it can contribute to catalytic converter overheating and eventual failure, which is a much more expensive repair.
Is P0038 the upstream or downstream O2 sensor?
P0038 refers to the downstream oxygen sensor on Bank 1, labeled Sensor 2. This sensor is located after the catalytic converter on the side of the engine that contains cylinder #1.
Can I clear P0038 and keep driving?
You can clear the code and continue driving, but if the underlying problem remains, P0038 will return. Clearing without fixing only resets the light temporarily and can delay other important diagnostics if new issues arise.
How do I know which O2 sensor to buy for P0038?
You need the Bank 1 Sensor 2 oxygen sensor. Use your VIN, engine size, and emission standard (federal vs. California, if applicable) when ordering. I recommend using a quality OEM or reputable aftermarket brand to avoid fitment and heater resistance issues.
Does P0038 always mean I need a new oxygen sensor?
No. While a failed sensor heater is common, P0038 can also be caused by wiring damage, a short to power, a bad connector, or a blown fuse or relay. Always inspect wiring and test the circuit with a multimeter before replacing parts.