DTC: O₂ Sensor Heater Circuit – Bank 1 Sensor 1 (Upstream) Malfunction

FUNCTION

The heater inside the O₂ sensor warms up the sensor quickly after engine start.
If the heater circuit fails → the sensor stays cold → poor readings → increased fuel consumption & rough idle.

✅ Possible Causes

Most Common

1. Heater element inside the O₂ sensor is open (sensor failed)

2. Blown fuse for O₂ sensor heater

3. Broken/shorted wires to the sensor

4. Corroded or loose O₂ sensor connector

5. ECM/PCM not providing proper heater control (rare)

🔧 Step-by-Step Diagnosis

1. Check O₂ Sensor Heater Fuse

Most cars have a fuse labeled:

O2 HTR, A/F Heater, EFI, ENG 1, HTR, etc.

If fuse blown → replace it.
If it blows again → wiring or sensor heater is shorted.

2. Inspect Wiring & Connector

Look at the Bank 1 Sensor 1 (upstream) O₂ sensor connector:

Check for:

Burnt wires (common near exhaust)

Melted insulation

Oil/water inside connector

Loose pins

Repair any wiring issue before replacing sensor.

3. Test O₂ Sensor Heater Resistance

Disconnect sensor & measure resistance across heater pins.

Normal value:

Typically 3–15 ohms (varies by car)

If:

Open circuit (∞ ohms) → heater burned out → replace sensor

0–1 ohm (short) → internal short → replace sensor

4. Check Power Supply

With ignition ON:

One heater wire should have battery voltage (12V).

The other is control/ground from ECM.

If no 12V → fuse, relay, or wiring fault.

5. Check ECM Control Side (Ground)

Use a test light or multimeter:

ECM will pulse/ground the heater circuit for a few seconds after engine start.

If no control → possible ECM fault (rare).

🛠️ Common Fixes

✅ Replace O₂ sensor (Bank 1 Sensor 1) – MOST COMMON
✅ Repair heater circuit wiring
✅ Replace blown fuse
✅ Clean or tighten sensor connector
✅ Repair ground issues
✅ ECM repair/replacement (very rare)

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