P0037 – O2 Sensor Heater Control Circuit Low (Bank 1, Sensor 2).

✅ Meaning of P0037

This code indicates that the rear O₂ sensor (Bank 1 Sensor 2) heater circuit is reading LOW voltage.
This is the downstream sensor, located after the catalytic converter.

The heater is used to warm up the sensor quickly. A low circuit signal means the ECM sees low voltage / low current, usually due to an open circuit, high resistance, or poor power/ground.

🔧 Common causes

1. Faulty O₂ sensor heater element (most common)

2. Blown O₂ sensor fuse

3. Broken / damaged wiring near exhaust

4. Poor connector contact (melted, water entry)

5. Open heater circuit in the sensor

6. High resistance in wires

7. ECM driver issue (rare)

🔍 Quick check you can do

1️⃣ Check the O₂ Sensor Fuse
Many cars have a dedicated fuse for O₂ heater circuits.
Look for fuses labelled:

OXY

O2 HT

EFI#2

A/F Heater
If blown → replace and test.
If it blows again → wiring short to ground.

2️⃣ Inspect Wiring & Connector

Bank 1 Sensor 2 connector is near the catalytic converter.
Look for: ✔ Melted wires
✔ Open or broken wires
✔ Oil/water inside connector
✔ Loose connector

Repair as needed.

3️⃣ Check Heater Resistance (Multimeter Test)

Unplug the sensor and measure resistance between the two heater pins.

Typical heater resistance:

3–20 ohms (varies by model)

If:
Open circuit (OL) → sensor heater is dead → replace sensor

Very high resistance → weak heater → replace sensor

4️⃣ Check Power & Ground to Heater

With ignition ON:

One pin should have battery voltage (12V)

The other pin is usually ECM-controlled ground

If no power → fuse or wiring issue
If power OK but heater not working → sensor faulty

🛠 Most common fix

✔ Replace Bank 1 Sensor 2 (downstream O₂ sensor)

Usually a direct fix for P0037 when wiring and fuse are good.

📍 Sensor location reminder 

Bank 1 = side of engine with cylinder #1

Sensor 2 = rear/downstream oxygen sensor
→ located after the catalytic converter.

Welcome to madurai car service 💐🙏.