P0137 OBD2 Code Guide
P0137 is a sensors diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
Code P0137 indicates that the Powertrain Control Module (PCM) has detected a persistently low voltage signal from the downstream oxygen sensor (Sensor 2) on Bank 1. Bank 1 refers to the engine bank that contains cylinder #1. Sensor 2 is located after the catalytic converter, monitoring its efficiency. A low voltage signal typically suggests a lean condition, a faulty sensor, an exhaust leak, or an issue with the sensor's wiring or connection, preventing it from reporting accurate oxygen levels in the exhaust gases. This can lead to increased emissions and potentially affect fuel economy.
Code verification standard
P0137 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0137 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0137 diagnostic path
- 1Visually inspect the Bank 1, Sensor 2 O2 sensor and its wiring harness for any signs of damage, fraying, corrosion, or loose connections. Also, check for any obvious exhaust leaks near the sensor.
- 2Connect an OBD-II scan tool and monitor the live data for Bank 1, Sensor 2. Observe its voltage readings. A persistently low voltage (e.g., consistently below 0.2V) confirms the code. Compare it to Bank 2, Sensor 2 (if applicable) for comparison.
- 3With the ignition off, disconnect the O2 sensor connector. Use a multimeter to test the resistance of the sensor's heater circuit (if applicable) and check for proper voltage supply (typically 12V for heater, 5V reference for signal) and ground at the vehicle's harness connector.
- 4Thoroughly inspect the entire exhaust system for any leaks, particularly upstream of the Bank 1, Sensor 2, or directly at the sensor's mounting point. An exhaust leak can introduce ambient air, causing a false lean reading.
- 5If all sensor and wiring tests pass, and no exhaust leaks are found, consider testing the PCM's signal input for the O2 sensor. This may require advanced diagnostic equipment and expertise.
Verify before repair
- - Replace the faulty Bank 1, Sensor 2 oxygen sensor.
- - Repair or replace damaged, corroded, or shorted wiring and connectors leading to the O2 sensor.
- - Repair any exhaust leaks located upstream or at the mounting point of the Bank 1, Sensor 2.
- - Address any underlying engine issues causing a consistently lean condition (less common for a downstream sensor, but possible if the catalytic converter is failing due to upstream issues).
Vehicle-specific pages to check next
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