DTC P0136 – O₂ Sensor Circuit Malfunction (Bank 1 Sensor 2)

Common Causes

1. Faulty O₂ Sensor (B1S2) – element worn out, internal heater issue.

2. Wiring damage – melted on exhaust, cut, corroded, rodent damage.

3. Poor sensor connector contact – moisture, loose pins.

4. Exhaust leak after catalytic converter.

5. ECU pin or ground issue (rare).

Symptoms

Usually no major drivability issues.

MIL ON (Check Engine Light).

Slight increase in fuel consumption (rare).

Sometimes catalytic converter efficiency codes may follow (P0420).

Step-by-Step Diagnostic Procedure

1. Visual Inspection

Inspect O₂ sensor wiring from catalytic converter area to harness.

Look for:
✅ Burning, cuts, rubbing
✅ Oil or water intrusion
✅ Loose connector

Fix any wiring issues first.

2. Check Sensor Voltage (Live Data)

Bank 1 Sensor 2 expected reading:

0.6–0.8 V steady when the engine is warm.

Should NOT fluctuate like Sensor 1.

If voltage is:

0.0–0.1 V → open circuit, broken wire or sensor faulty.

1.0 V fixed → short to power.

Fluctuating rapidly → exhaust leak or sensor fault.

3. Check Heater Circuit (Very Important)

Even though P0136 is not specifically heater-related, many times the heater circuit is weak.

Unplug sensor.

Measure resistance between heater terminals → typically 3–20 ohms.

If open circuit or very high resistance, replace sensor.

Check power supply:

One side gets battery voltage (12V) with ignition ON.

Other side → ECU ground control.

4. Check Exhaust for Leaks

Look for leaks after catalytic converter.

A leak will cause sensor to read wrong values.

5. Substitute Known Good Sensor

If wiring and signals are OK → replace with OEM-quality downstream O₂ sensor.

Recommended Repair

✅ Replace Bank 1 Sensor 2 O₂ sensor (use OEM brand – NTK, Denso, Bosch).
✅ Repair or replace damaged wiring.
✅ Fix exhaust leaks.
✅ Clear codes and perform a short road test.

Welcome To Madurai Car Service 💐🙏🏻.