System: Powertrain (P-Code) Coverage: SAE Standard (Generic) Fault Family: o2_sensor_circuit

Code P0138: O2 Sensor Circuit High Voltage Bank 1 Sensor 2

Diagnostic & Technical Explanation

Code P0138 (O2 Sensor Circuit High Voltage Bank 1 Sensor 2) sets when the ECM sees an open circuit, a stuck/biased voltage, or no signal activity from an oxygen sensor's signal circuit. Causes are a contaminated or worn-out sensor element, an exhaust leak near the sensor bung skewing readings, or damaged sensor wiring.

Probability-Ranked Repair Procedures (3 Ranked Fixes)

Rank #1

Inspect for exhaust leaks near the O2 sensor

Easy DIY

Parts Estimate: $5.0–$40.0 USD Labor Estimate: 0.6 Shop Hours

1. Inspect the exhaust manifold and pipe joints near the sensor bung for leaks
2. Listen and smoke-test for exhaust leaks upstream of the sensor
3. Replace gaskets or tighten fasteners as needed
4. Clear codes and monitor sensor voltage trace

Required Replacement Parts: 🔧 Exhaust manifold/pipe gasket

Rank #2

Replace oxygen sensor

Moderate DIY

Parts Estimate: $50.0–$180.0 USD Labor Estimate: 0.6 Shop Hours

1. Identify the affected bank/sensor position
2. Remove the sensor with an O2 sensor socket
3. Apply anti-seize to threads (avoid the tip) and install the new sensor
4. Clear codes and confirm a normal switching voltage trace

Required Replacement Parts: 🔧 Oxygen sensor (bank/position-specific) · 🔧 Anti-seize compound

Rank #3

Repair O2 sensor signal circuit wiring

Professional Required

Parts Estimate: $10.0–$60.0 USD Labor Estimate: 1.2 Shop Hours

1. Back-probe the signal and ground at the connector with the engine running
2. Voltage-drop test the circuit back to the ECM
3. Repair chafed or corroded wiring near the exhaust with high-temp splices
4. Confirm proper switching activity

Required Replacement Parts: 🔧 High-temperature wiring repair kit

Code P0138: O2 Sensor Circuit High Voltage Bank 1 Sensor 2

Probability-Ranked Repair Procedures (3 Ranked Fixes)

Inspect for exhaust leaks near the O2 sensor

Replace oxygen sensor

Repair O2 sensor signal circuit wiring

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