P0031: HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
Quick Answer
Safe to drive (short-term)
P0031 means the engine computer measured too little current or too low a voltage in the heater circuit of the upstream oxygen sensor on bank 1, the one before the catalytic converter. On many cars that is exactly what a burned-out heater, a blown fuse or a broken supply wire produces. Until exhaust heat warms the sensor, the engine runs on a fixed, richer mixture. A new upstream sensor typically costs about 100 to 300 EUR fitted.
- Severity
- Low · Emissions
- Estimated repair cost
- From €1 to €400+, varies by vehicle
€1 or €400, depending on your car.
- Replace O2 sensor heater fuse€1–€3
- Replace upstream O2 sensor (OEM quality or wideband)€130–€400
A scan shows whether P0031 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P0031 mean?
P0031 is a emissions-related diagnostic trouble code classified as low severity.
Where it is on the car
- Engine
- Oxygen sensor before the converter (sensor 1)
- Catalytic converter
- Oxygen sensor after the converter (sensor 2, or 3 on some cars)
- Silencer and tailpipe
This code is about the sensor's heater, which warms it up after a cold start. The usual causes are a blown fuse, a damaged connector or wire, or a worn-out heater inside the sensor. On some cars this sensor is an air-fuel ratio sensor, which sits in the same place.
What are the symptoms of P0031?
- Check engine light on, usually with no change in how the car drives once warm
- Slightly higher fuel use on short trips and in cold weather
- Engine stays in open loop (fixed, richer mixture) longer after a cold start
- Code returns within seconds or minutes of starting the engine after being cleared
- Possible rejection at an emissions inspection while the warning light is on
What causes P0031?
Burned-out (open) heater element inside the upstream oxygen or air-fuel ratio sensor
: high
Blown heater fuse, which cuts power and makes the heater circuit read low
: medium
Broken, corroded or unplugged wiring or connector in the heater supply or control circuit
: medium
Faulty heater relay or main relay feeding the sensor heater
: low
Control wire shorted to ground, or a faulty heater driver in the engine computer (rare)
: low
Is it safe to drive with P0031?
Generally yes, for short-term driving. Safe to drive in the short term. The upstream sensor starts working once exhaust heat warms it, so the car drives normally when warm; you lose some fuel economy on short trips and cold-start emissions rise. Book the repair soon, because the warning light hides any new fault and can get the car rejected at an emissions inspection.
How do you diagnose P0031?
- Read all stored codes and freeze frame. P0031 together with P0037 or other heater codes points to a shared fuse, relay or supply wire rather than two failed sensors
- Check the heater fuse named in the owner's manual or on the fuse box lid (often labelled for the O2 or A/F sensor heater, or shared with the engine management). Replace it if blown, and if it blows again look for a short
- Unplug the Bank 1 Sensor 1 connector and measure the resistance across the two heater pins. Wideband air-fuel ratio sensors often read around 2 ohms and many narrowband sensors between about 3 and 15 ohms; check your car's specification. An open circuit means a burned-out heater
- With the key on, check for battery voltage on the heater supply pin on the harness side. No voltage points to the fuse, relay or supply wire
- Check the control wire from the sensor to the engine computer for breaks and for a short to ground, and inspect the connector for corrosion or pushed-back pins
- After the repair, clear the code and restart. On many cars P0031 is checked soon after start-up, so a genuine fix should keep it from returning. With a generic OBD2 reader, confirm the fuel system goes into closed loop within a few minutes and the oxygen sensor heater readiness monitor completes
How much does P0031 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace O2 sensor heater fuse | €1–€3 | €0–€0 | €1–€3 | Easy |
| Replace O2 sensor heater relay | €10–€40 | €20–€60 | €30–€100 | Easy |
| Repair wiring or connector | €5–€20 | €40–€120 | €45–€140 | Moderate |
| Replace upstream O2 sensor (Bank 1) | €50–€180 | €50–€120 | €100–€300 | Moderate |
| Replace upstream O2 sensor (OEM quality or wideband) | €80–€280 | €50–€120 | €130–€400 | Moderate |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
P0031 on specific vehicles
P0031 on Nissan
Nissan Juke (HR16DE/MR16DDT) · Nissan 350Z (VQ35HR)
Related diagnostic codes
Common questions about P0031
- What does code P0031 mean?
- P0031 means the heater circuit of the Bank 1 Sensor 1 oxygen sensor (the upstream sensor before the catalytic converter, on the side of the engine with cylinder 1) is reading low: too little current or too low a voltage. On many cars that means the heater element has burned out or has lost its power supply.
- Is P0031 serious?
- Not in the short term. The sensor still works once hot exhaust has warmed it, so the engine runs normally when warm. Expect slightly higher fuel use on short trips and higher cold-start emissions. The warning light can get the car rejected at an emissions inspection (rules vary by country), so fix it soon.
- Can a bad fuse cause P0031?
- Yes. If the heater fuse blows, the heater gets no power and the circuit reads low, which is exactly what P0031 describes. The same fuse often feeds other sensor heaters, so check it first, especially when several heater codes appear together.
- How do I test the oxygen sensor heater for P0031?
- Unplug the sensor and measure the resistance between its two heater pins with a multimeter. Wideband air-fuel ratio sensors often read around 2 ohms, many narrowband sensors between about 3 and 15 ohms; your car's specification is the reference. An open circuit (no reading) means the heater has burned out and the sensor must be replaced, because the heater is built into it.
- How much does it cost to fix P0031?
- A blown fuse costs 1 to 3 EUR. A heater relay costs about 30 to 100 EUR fitted, and a wiring or connector repair about 45 to 140 EUR. A new upstream oxygen sensor costs roughly 100 to 300 EUR fitted, or 130 to 400 EUR with an OEM-quality or wideband air-fuel ratio sensor.
- Can a generic OBD2 scanner diagnose P0031?
- A generic OBD2 reader shows this code, its freeze frame, the upstream sensor reading, whether the fuel system is in open or closed loop, and the readiness monitors, including the oxygen sensor heater monitor. It cannot show heater current, heater duty cycle or the manufacturer's heater adaptation values; those need the brand's own diagnostic software.
Read our detailed guides
Sources
- nijutech.com nijutech.com/p0031_p0032_a_f_sensor_1_heater-860.html
- en.wikipedia.org en.wikipedia.org/wiki/Nissan_Juke
- 350z.se 350z.se/fsm/coupe/2007/ec.pdf
- en.wikipedia.org en.wikipedia.org/wiki/Nissan_350Z