P0157 code definition
Oxygen Sensor Circuit Low Voltage (Bank 2 Sensor 2)
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. It’s 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 and both can cause premature failure of the catalytic converter. The oxygen sensor switches back and forth from low voltage (lean) to high voltage (rich). When this code is stored by the power control module (PCM), it means that the oxygen sensor has remained at a low voltage for too long.
What causes the P0157 code?
- Faulty oxygen sensor (bank 2 sensor 2)
- Insufficient fuel pressure
- False reading of the oxygen sensor as a result of holes in the exhaust
- Corrosion of the rear oxygen sensor’s connector
- Fuel or coolant leaks on the rear oxygen sensor
- Broken, shorted or exposed wires
- Malfunction of the engine coolant temperature sensor
- Defective power control module (PCM)
- Update required for power control module (PCM)
What are the symptoms of the P0157 code?
- Increase in fuel consumption
- Check Engine Light is on
- Engine runs rough or idles poorly
- In some rare cases, there will be no symptoms noticed by the driver.
How does a mechanic diagnose the P0157 code?
Collects trouble code and views freeze frame data from the OBD-II scanner.
Also uses scan tool to monitor oxygen sensor voltage to see if it is switching properly.
If an engine coolant temperature sensor trouble code is present as well, view its live data to see if it is working properly.
Checks fuel pressure with fuel pressure gauge. Proper fuel pressure should be at 40 psi.
Inspects the exhaust for air leaks in the manifold and pipes.
Inspects the rear oxygen sensor wires for shorts, breaks or exposure.
The computer may need to be updated at the dealer.
Advance diagnosis may also be necessary to determine if there is a problem with the Primary Control Module (PCM).
Common mistakes when diagnosing the P0157 code
- Replacing the oxygen sensor without confirming it is bad
- Not inspecting the condition of the oxygen sensor wires
- Not being able to inspect the condition of the exhaust
How serious is the P0157 code?
The P0157 trouble code is considered moderately serious. It can cause drivability issues and has the potential of causing the car to stall out. If not addressed, damage to the catalytic converter can be done over time, which will be expensive to fix. It is recommended to have this problem addressed as soon as possible.
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
- Replacing the power control module (PCM) or having it updated, if necessary
Additional comments for consideration regarding the P0157 code
If the oxygen sensor has ceased up in the exhaust pipe, which is common, specialty tools will be required. An oxygen sensor set will make it easier to reach an oxygen sensor that is positioned awkwardly, and a propane torch is used as a heating element to assist in the removal.
Need help with a P0157 code?
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This article originally appeared on YourMechanic.com as P0157 OBD-II Trouble Code: 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2) and was authored by Jamahl Walker.