P0038 Code: O2 Sensor Heater Control Circuit High (Bank 1 Sensor 2)
The heater circuit of the sensor behind the bank 1 converter shows a short to power or excess current.
At a glance
Severity: Low
- Meaning
- O2 Sensor Heater Control Circuit High (Bank 1 Sensor 2)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$300
- DIY difficulty
- Moderate
P0038 sets when the engine computer sees too much voltage or current in the heater circuit of the oxygen sensor behind the bank 1 catalytic converter. Either the control wire stays near battery voltage when the computer tries to pull it low, or the heater draws more current than the driver allows. Underneath the car there are two typical ways this happens. The sensor's heater can short internally once it's hot, or the pigtail can sag onto the converter or exhaust pipe, where the insulation melts and the feed and control wires fuse together. Salt water trapped in the connector can also bridge the heater pins. A shorted downstream heater often blows the fuse it shares with the upstream sensor, so P0038 is frequently followed by low codes on the other heaters.
Can I keep driving? Driving doesn't hurt the engine, but a hard short can wreck the computer's heater driver and blow a shared fuse. Get it checked rather than repeatedly clearing the code.
How to read P0038
- P Powertrain
- 0 Generic (SAE)
- 0 Fuel/air & emissions (aux.)
- 38 Specific fault
Symptoms
- Check engine light, often only once the exhaust is fully hot after a longer drive
- Heater fuse blows and upstream heater codes appear on the next start
- Heater current in scan data far above normal before the computer shuts it off (on makes that show it)
- Melted or shiny, fused insulation visible on the sensor pigtail under the car
- No change in engine performance
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Downstream sensor heater shorting internally when hot
- Pigtail resting on the converter or pipe, insulation melted and wires fused together
- Salt water or corrosion bridging heater terminals in the underbody connector
- Incorrect sensor fitted, or pigtail spliced with heater and signal wires mixed up
- Heater driver damaged inside the engine computer
- Broken exhaust hanger letting the pipe push against the harness
Diagnosis step by step
Use the unplug test to split sensor from harness
Clear the code, unplug the downstream sensor and start the engine. If the computer now logs the low code (P0037) instead of P0038, the harness is healthy and the short is inside the sensor. If P0038 comes straight back with the sensor unplugged, the short is in the wiring or the computer.
Tools: OBD-II scanner
Inspect the pigtail along the exhaust
With the car safely raised, run a hand and a flashlight along the whole pigtail. Melted, glossy or fused insulation next to the converter shell or pipe tells the story. Also check that the exhaust hangers are intact; a sagging pipe is often what pushed the harness out of its clips.
Tools: Flashlight
Measure the heater and its insulation
Measure across the heater pins on the sensor side: a narrowband heater well below its spec (for example under 2 ohms where 5 to 15 is expected) is shorted. Then measure from each heater pin to the sensor body and signal pins; any reading other than open means internal breakdown.
Tools: Multimeter
Check the harness for a short to power
With the sensor unplugged and key on, the control pin on the harness side should not show full battery voltage. If it does, disconnect the battery and the computer connector and measure between the control and feed wires; continuity confirms they're touching somewhere, usually at the melted spot you found.
Tools: Multimeter
Repair wiring the right way
Cut out any melted section and splice in high-temperature wire with sealed heat-shrink connectors, staggering the joints. Refit the harness in its clips with at least a few inches of clearance from the exhaust, adding a heat sleeve where the gap is small.
Tools: Pliers
Replace the fuse with the correct rating and verify
Fit a new fuse of the rating printed on the fuse box lid, never higher. Clear codes, run the engine until the exhaust is fully hot and confirm no heater codes return on any sensor.
Tools: OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean and reseal the underbody connector | Yes | $0–$50 |
| Downstream O2 sensor, part only | Yes | $40–$140 |
| Downstream O2 sensor replaced at a shop | No | $130–$300 |
| Repair melted harness and fit heat sleeve | No | $100–$300 |
| Replace broken exhaust hanger | Yes | $20–$120 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P0038 turns on the check engine light, which fails the OBD-II portion of a state emissions test. If the short also blew a shared fuse, several heater and O2 monitors will be incomplete until the repair is done and the car has been driven.
Frequently asked questions
Why did P0038 come back as P0037 after I unplugged the sensor?
That's good news. With the sensor unplugged the circuit is open, so the computer correctly reports low. It proves the wiring isn't shorted to power and that the short was inside the sensor you just unplugged.
Why do I now have upstream heater codes too?
On many vehicles the upstream and downstream heaters share one fuse. When the downstream heater shorted, it blew that fuse, and the upstream heater lost its power as well. Fix the short first, then replace the fuse and clear all the codes.
Can I repair a melted pigtail with ordinary wire and tape?
Not near the exhaust. Standard insulation and electrical tape soften and fall off in that heat, and you'll soon have the same short again. Use high-temperature wire, sealed crimp connectors and a heat sleeve, and fix the routing so it can't happen twice.
Is P0038 more urgent than P0037?
Slightly. An open heater just stops working, while a short stresses the heater driver in the engine computer and can take out a shared fuse. Neither affects drivability much, but the short is worth fixing sooner.