P0136 - O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

Downstream O2 sensor circuit issue (B1S2).

Code Overview

Downstream O2 sensor circuit issue (B1S2).

Common Causes

• Failing downstream oxygen sensor on bank 1 sensor 2
• Wiring or connector fault in the sensor circuit
• Exhaust leak ahead of the downstream sensor
• Catalyst issue affecting downstream sensor behavior

Symptoms

• Check-engine light with little or no drivability complaint
• Failed emissions readiness or inspection
• Downstream O2 data may appear flat or erratic

Diagnostic Steps

1. Inspect the bank 1 sensor 2 wiring and connector near the exhaust
2. Check for exhaust leaks ahead of the downstream sensor
3. Verify downstream sensor activity on the scan tool after warm-up
4. Look for catalyst-related companion codes before replacing parts

Repair Difficulty

Moderate

General difficulty estimate for the most common repair path.

Likely Repairs & Cost Guides

Use test results to confirm the fault before pricing the repair.

Related OBD Codes

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Next Steps

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