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Auto ... 2/26/2018

2014 BMW 550i GT Base 8 Cyl 4.40L

Preventive Maintenance

What causes O2 Sensor Circuit Low Voltage if getting P0157 OBD-II Trouble Code while diagnosing a car?

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PartsAvatar Ca

PartsAvatar Ca 2/26/2018

What the P0157 code means?

The oxygen sensor that trouble code P0157 refers to is located in the rear of the exhaust and behind the catalytic converter. Its main function is to regulate the amount of oxygen that comes from the catalytic converter. A lean mixture of oxygen and gas means that there is too much oxygen in the exhaust. A rich mixture of oxygen and gas means that there is not enough oxygen in the exhaust. Neither a lean mixture or rich mixture is good for the catalytic converter nor can both cause premature failure of the catalytic converter.

What causes the P0157 code?

Defective Oxygen Sensor
Defective Oxygen Sensor Heater circuit
Low Fuel Pressure
Defective Engine Coolant Temperature Sensor
Defective sensor wiring and/or circuit problem

What are the symptoms of the P0157 code?

MIL (Malfunction Indicator Lamp) illumination
Engine performance issues
Engine running rough
Engine running rich
Engine running lean

Common mistakes when diagnosing the P0157 code:

Technicians report replacement of oxygen sensors, when lean or rich engine conditions are the cause of incorrect readings, is fairly common. Replacement of the incorrect oxygen sensor is also a possibility.

What repairs can fix the P0157 code?

Replacing the rear oxygen sensor
Repairing of broken circuitry or shorted wires going to the oxygen sensor
If the fuel pressure is abnormal, repairing the cause of the abnormality
Repairing the engine coolant temperature sensor if it is faulty

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