How to fix code p0031 on Nissan Note

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 P0031 on a Nissan Note HO2S Heater Control Circuit Low (Bank 1 Sensor 1)` 7408

That’s the upstream O2 sensor before the cat. The ECU thinks the heater inside the sensor isn’t getting enough power. 7408

What usually causes it

1. Dead O2 sensor heater - most common on older Notes

2. Damaged wiring/connector - heat from the exhaust burns the harness

3. Blown fuse / no 12V supply to the heater

4. Bad ground or open circuit  in the heater control wire

5. Rare: ECM/PCM fault

How to fix it - easiest to hardest

1. Check the basics first

- Scan and clear the code. Test drive 10-15 min. If it comes back, it’s real.

- Check fuse for O2 heater. On most Nissan Notes it’s labeled “O2 HTR” or “ENG CONT” in the engine bay fuse box. If blown, replace it. 

2. Inspect wiring and connector

Look at the harness for the upstream sensor - it runs close to the exhaust manifold. Common for it to melt or chafe.

- Look for frayed, burnt, or loose wires

- Check the connector for corrosion or bent pins.

3. Test power and ground at the sensor connector

You’ll need a multimeter:

1. Unplug the sensor. Key ON, engine OFF.

2. Check for 12V+ on the heater power wire vs engine ground. If no voltage, you’ve got an open/short in the power feed.

3. Check continuity to ground on the heater ground wire. Should be <5Ω. 9a6eb639

4. Test the sensor heater itself

Set multimeter to ohms and check resistance between the 2 heater wires on the sensor side.

- Good: usually 3-15Ω

- Open/infinite: heater is dead → replace the sensor.

5. Replace the sensor if needed

Bank 1 Sensor 1 is the upstream sensor. On the Note 1.2/1.6 it’s screwed into the exhaust manifold. Use an O2 sensor socket. Use anti-seize on the threads. 

After replacement, clear codes and drive. The code should stay gone. 


Quick symptoms you’ll notice

- Check engine light on

- Slightly worse fuel economy

- Engine might run a bit rough when cold ec4e


*Most likely fix on a Niss

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