O2 Sensor Circuit Low Voltage Bank 1 Sensor 2
Diagnostic trouble code P0137 indicates that the engine control module (ECM) has detected a persistently low voltage signal from the downstream oxygen sensor on Bank 1. This means the sensor's output has remained below the acceptable threshold (typically under 0.2 volts) for a predetermined amount of time, suggesting a lean exhaust condition, an exhaust leak, or a circuit fault.
This code primarily affects emissions monitoring rather than engine performance, so the vehicle is generally safe to drive in the short term. However, it should be diagnosed and repaired to ensure emissions compliance and prevent potential long-term issues.
Common symptoms
- Illuminated Check Engine Light
- Failure to pass a state emissions inspection
- No noticeable drivability issues (most common)
- Audible exhaust leak noise from under the vehicle
- Slight decrease in fuel efficiency
Likely causes
- Faulty Bank 1 Sensor 2 oxygen sensor
- Exhaust leak upstream of or near the downstream O2 sensor
- Damaged, melted, or corroded O2 sensor wiring or connector
- Short to ground in the O2 sensor signal circuit
- Faulty catalytic converter
- Engine control module (ECM) software issue or failure (rare)
What to check before replacing parts
Visually inspect the O2 sensor wiring and connector.
Look for: Look for melted wires from exhaust heat, corrosion in the connector pins, or physical damage that could cause a short to ground.
Listen and feel for exhaust leaks near the catalytic converter and O2 sensor.
Look for: Check for soot marks or audible ticking noises that indicate outside air is entering the exhaust stream and skewing the sensor reading.
Monitor Bank 1 Sensor 2 voltage using a scan tool with live data.
Look for: Observe if the voltage is stuck below 0.2 volts; if it responds to a snap-throttle test by briefly spiking rich, the sensor may be functioning but reading a true lean condition or leak.
Disconnect the O2 sensor and test the signal wire for a short to ground.
Look for: Using a multimeter, check for continuity between the signal wire and chassis ground; any continuity indicates a short in the wiring harness.
Test the O2 sensor heater circuit resistance.
Look for: Measure the resistance across the heater pins of the sensor; an open circuit or out-of-spec resistance means the sensor cannot reach operating temperature and must be replaced.
This page explains the generic P0137 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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