P0031 means HO2S Heater Control Circuit Low (Bank 1 Sensor 1). The computer has found the heater control circuit for the bank 1 sensor 1 oxygen sensor, before the catalytic converter, reading low voltage, so the sensor may not warm up quickly. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0031 means
Oxygen sensors measure the oxygen left in the exhaust. Sensor 1 sits before the catalytic converter and is used for fuel control; sensor 2 sits after it and mainly monitors the converter. Most sensors have a heater so they start working soon after a cold start. A traditional zirconia sensor switches between about 0.1 volt (lean) and 0.9 volt (rich); many newer upstream sensors are wide-band air-fuel sensors that report differently, so check which type your engine uses.
P0031 symptoms
- Check engine light
- Slower warm-up of fuel control after a cold start
- Possible poor fuel economy
Common causes of P0031
- Heater control wire shorted to ground
- Failed oxygen sensor heater
- Wiring melted on the exhaust
How to diagnose P0031
- Check the oxygen sensor heater fuse
- Measure heater resistance at the sensor connector
- Check power and the control circuit to the heater
- Inspect wiring near the exhaust
Can you drive with P0031?
Usually yes; fix it to restore normal fuel control and emissions readiness.
P0031 tips
A heater circuit low code often means the control wire is shorted against the exhaust; check the harness routing near the manifold.
Will P0031 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0031 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0135 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) |
| P0032 | HO2S Heater Control Circuit High (Bank 1 Sensor 1) |
| P0030 | HO2S Heater Control Circuit (Bank 1 Sensor 1) |
Guides that help
When it is more than a sensor
Oxygen sensor codes are fixed with a sensor, wiring, a fuse or an exhaust leak repair. An engine burning oil or coolant contaminates sensors quickly; if new sensors keep failing, check for blue or white exhaust smoke and a head gasket leak, and compare engines by code on our engines page if the engine is worn out.
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