OBD-II Code · Sensors
P0038
HO2S Heater Control Circuit High (Bank 1 Sensor 2)
Severity
low
Lowest on our scale. Fix it when convenient.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$150–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Downstream O2 heater circuit reading high on bank 1.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Failed sensor heater elementMost common
- Short to power
- Wiring issue
Read the full diagnostic procedureP0038 indicates the downstream Bank 1 heater control circuit is stuck high — open heater element, broken ground, or a PCM driver that won't switch.
P0038 indicates the downstream Bank 1 heater control circuit is stuck high — open heater element, broken ground, or a PCM driver that won't switch.
Cheapest test first
- ohm the heater cold at the sensor — 2-10 ohms is normal (11-14 ohms for Denso Toyota downstream), OL means the element is blown.
- If the heater ohms good, back-probe the control wire and scope it during key-on; the PCM should be pulling the line low with PWM pulses ramping in duty cycle.
- A flat 12V trace with no switching means the driver isn't commanding ground — verify the harness isn't open between the sensor and PCM by ohming end-to-end with the PCM connector unplugged.
- Heater current should reach 0.3-1.5A at peak warm-up; zero current confirms an open.
- Closed-loop fuel control on the upstream sensor will still work, but catalyst-efficiency monitors will not run until the downstream heater functions.
- Expensive misdiagnosis: replacing the catalytic converter for a perceived efficiency code when the real problem is a dead downstream heater preventing the monitor from running.
Vehicle-specific patternsHonda K24 (Accord/CR-V/Element 2003-2012) downstream narrowbands open internally with age, typically past 130K miles, with no harness fault — straigh…
Honda K24 (Accord/CR-V/Element 2003-2012) downstream narrowbands open internally with age, typically past 130K miles, with no harness fault — straight Denso 234-4621 replacement. Ford 5.4L 3V Triton (F-150/Expedition 2004-2010) develops broken ground splices in the downstream harness near the transmission tunnel. Toyota 1GR-FE 4.0L V6 (Tacoma/4Runner/FJ Cruiser 2005-2015) downstream sensors open at the connector pin where moisture intrudes. GM 3.6L LFX/LLT (Traverse/Acadia/Enclave 2009-2016) sees downstream heater opens at the catalyst-monitor sensor after extended idle service.
Estimated repair$100 to $360.
Look up another code
P0038 — frequently asked
What does a P0038 code mean?
Downstream O2 heater circuit reading high on bank 1.
What causes a P0038 code?
Common causes: Failed sensor heater element; Short to power; Wiring issue.
What are the symptoms of a P0038 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0038 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $150-$400.
How do I diagnose a P0038 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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