Code Definition

P1157 — Lack of Downstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank 2

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Ford

About P1157

P1157 is a manufacturer-specific powertrain diagnostic trouble code recorded for Ford vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1157 is stored, the module has detected 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.

P1157 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Powertrain Control Module (PCM) monitors the downstream Heated Oxygen Sensor (HO2S) on Bank 2, located after the catalytic converter, to assess catalyst efficiency and on some applications to fine trim fuel delivery. DTC P1157 sets when this downstream Bank 2 sensor fails to switch and stays biased lean during operation, so the PCM cannot confirm normal post catalyst oxygen activity. Bank 2 is the cylinder bank that does not contain cylinder number 1. A persistent lean indication downstream can come from an exhaust leak after the converter, a contaminated or aged sensor, wiring problems, o...

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