What does it mean?
P1157 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Air Fuel Ratio (A/F) Sensor (Sensor 1) AFS Line High Voltage .
Symptoms
- Malfunction indicator lamp on with the engine locked in open loop
- Higher fuel consumption and reduced power
- Rough idle and hesitation, particularly while the engine is warming up
- Black smoke or a strong exhaust smell if fuelling is thrown off
- Emissions test failure with the oxygen sensor monitor incomplete
Likely causes
- Short to battery voltage or to another powered circuit in the sensor harness
- Open in the sensor signal or reference line letting the input float high
- Water and corrosion in the connector creating a leakage path between pins
- Failed sensing element inside the air/fuel ratio sensor
- Melted or chafed pigtail where it runs alongside the exhaust
- Poor sensor ground raising the measured voltage at the module
- Incorrect sensor fitted, whose output range does not match what the controller expects
How to fix it
- Read the sensor value in live data and check whether it is pinned at a fixed high level regardless of throttle
- Disconnect the sensor and see whether the reading changes; a value that stays high points to a harness short or an open input
- Test the signal wire for a short to battery voltage with the sensor unplugged and the key on
- Check continuity of the signal and reference lines from the connector to the PCM (powertrain control module)
- Inspect the connector for water, corrosion and melted plastic, then dry and repair as needed
- Measure the sensor ground circuit for voltage drop while the engine runs
- Fit the correct specification sensor once the wiring checks good, then confirm closed loop control returns