P0031 — O2 Sensor Heater Control Circuit Low (Bank 1 Sensor 1).

✅ Meaning of Code P0031

P0031 = Oxygen Sensor (Bank 1 Sensor 1) Heater Control Circuit Low

Bank 1 = side of engine with cylinder 1
Sensor 1 = the O₂ sensor before the catalytic converter (upstream)

“Circuit Low” means the ECM/ECU is seeing low voltage in the heater circuit — usually due to open circuit, high resistance, or poor power/ground supply.

🔧 Common Causes

1. Faulty O2 sensor (heater element open) – MOST COMMON

2. Blown O2 sensor heater fuse

3. Damaged wiring harness
– melted wires near exhaust
– broken wire inside insulation
– corroded connector pins

4. Poor ground connection

5. ECM/ECU driver fault (rare)

🔍 Quick Diagnostics (For Your Workshop)

1. Check O2 Sensor Heater Fuse

Most cars have a dedicated fuse for O2 heater circuits.
Look for names like:

HTR

A/F Heater

OXY HTR

If fuse is blown → heater element shorted → replace O2 sensor.

2. Inspect Wiring

Check the harness near:

exhaust manifold

pipes

catalytic converter

Look for:

burnt insulation

wires touching hot metal

loose or corroded connectors

Fix any damage → clear codes → test drive.

3. Test Sensor Heater Resistance

Unplug O2 sensor.
Use multimeter (ohms).

Typical heater resistance:

3–15 Ω (depending on vehicle)

If reading is:

Open circuit OL / very high Ω → heater burned out → replace sensor

Very low < 2 Ω → shorted heater → replace sensor

4. Check Power Supply to Heater

With ignition ON:

One wire should have battery voltage (~12V)

Other wire is ECU-controlled ground

If no power:

check fuse

check relay

check for broken wire

If power is OK but ECU ground control signal missing:

may be ECU driver problem (rare).

🛠️ Common Fixes

✔ Replace Bank 1 Sensor 1 O2 sensor
✔ Repair melted wiring
✔ Replace blown heater fuse
✔ Clean or tighten ground connections
✔ Repair ECU driver (rare)

📌 Important Tip

Always use OEM or high-quality O2 sensors. Cheap sensors often fail heater circuits quickly.

Welcome to madurai car service 💐🙏.