P0157 - O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Downstream O2 sensor signal voltage low (B2S2).

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Code Overview

Downstream O2 sensor signal voltage low (B2S2).

Common Causes

• Failing downstream oxygen sensor on bank 2 sensor 2
• Exhaust leak affecting the downstream reading
• Wiring fault or poor terminal contact in the sensor circuit
• Actual lean-running condition on bank 2

Symptoms

• Check-engine light with little or no drivability complaint
• Failed emissions readiness or inspection
• Downstream O2 data may stay low on the scan tool

Diagnostic Steps

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

Repair Difficulty

Moderate

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