Code Definition

P0139 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0139

P0139 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0139 is stored, the module has detected a signal or supply voltage lower than the expected operating range; a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0139 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The P0139 fault code is set when the Engine Control Module (ECM) detects that the oxygen sensor in Bank 1, Sensor 2, has a slower response time than expected. This sensor is usually located downstream in the exhaust system, after the catalytic converter. The slow response refers to the sensor's delayed adjustment in its voltage output in response to changes in the oxygen content of the exhaust gas. A slow response can impair the ECM’s ability to accurately monitor the efficiency of the catalytic converter. Causes for a slow response might include an aging or contaminated sensor, issues with ...

Join TaT to view the complete code information and diagnostic details.

Quick Facts