DTC P0150: O2 Sensor Circuit Malfunction (Bank 2, Sensor 1).

Bank 2 → The side of the engine without cylinder #1

Sensor 1 → The upstream / pre-catalytic oxygen sensor

The ECU is seeing no signal, an incorrect signal, or an unstable signal from that sensor circuit

This is not always a bad O2 sensor—wiring and exhaust issues are common.

Common Causes (In Order of Likelihood)

1. Faulty O2 sensor (Bank 2 Sensor 1)

2. Wiring damage

Melted insulation near exhaust

Broken or corroded connector pins

3. Exhaust leak before the sensor

4. Heater circuit failure (blown fuse, bad ground)

5. ECU issue (rare)

Step-by-Step Diagnostic Process (Workshop Method)

🌟 Quick Visual Inspection (Very Important)

Locate Bank 2 Sensor 1

Check:

Burnt wires

Oil or coolant contamination

Loose or broken connector

Inspect exhaust manifold for cracks or leaks

⏱️ This alone fixes many P0150 cases.

🌟 Scan Tool Live Data Check

With engine fully warm:

Monitor B2S1 O2 voltage

Normal operation:

Fluctuates between 0.1–0.9V

Faulty readings:

Stuck at 0V or 1V

No movement

Very slow response

➡️ If no activity, suspect wiring or sensor failure.

🌟 Heater Circuit Test (Multimeter)

Key ON, engine OFF:

Measure resistance across heater pins

Typical range: 3–14 ohms (check vehicle spec)

Check for:

12V supply on heater power wire

Good ground

❌ No voltage = fuse, relay, or wiring issue
❌ Open circuit = bad sensor

🌟 Signal Wire Test

Back-probe signal wire:

Should show ~0.45V reference

Wiggle test harness while watching live data

Voltage drop = broken wire inside insulation

🌟 Swap Test (If Applicable)

If vehicle uses same sensor type on Bank 1:

Swap B1S1 ↔ B2S1

Clear codes and test drive

✅ Code follows sensor → Replace sensor
❌ Code stays → Wiring or exhaust issue

Replacement Tips (If Sensor Is Bad)

Use OEM or high-quality brand (Denso, Bosch, NTK)

Avoid cheap universal sensors

Apply anti-seize (if not pre-coated)

Torque correctly (don’t overtighten)

Driveability Symptoms You May See

Poor fuel economy

Rough idle

Hesitation

Check Engine Light only (sometimes no symptoms).

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