P0157 – Meaning, Causes, Symptoms, & Fixes

Code P0157 Definition

O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2)

What Does P0157 Mean?

Oxygen sensor 2 is the downstream oxygen sensor in relationship to the catalytic converter. It measures the air-fuel ratio coming out of the catalytic converter to ensure the catalytic converter is functioning properly. The powertrain control module constantly flip-flops between rich and lean air-fuel mixtures due to the input from the upstream oxygen sensor (sensor 1). Whereas, the downstream oxygen sensor (sensor 2) should produce a steady voltage of approximately 0.1-.95 volts if the catalytic converter is doing its job properly and there are no problems with the engine’s air-fuel ratio. When trouble code P0157 is set, this indicates that there is low voltage (roughly 450 millivolts or less) for more than 20 seconds coming from the bank 2 sensor 2 oxygen sensor.

What Are the Symptoms of Code P0157?

• Check Engine Light
• Possible exhaust leaks
• Exhaust odor
• Vehicle running rough
• Lack of power

*No adverse conditions in some cases

What Is the Cause of Code P0157?

• Faulty oxygen sensor (most common)
• Short on voltage to O2 circuit
• Exhaust leaks
• Fuel pressure low
• Engine running lean

How Serious is Code P0157? – Moderate 

Driving with trouble code P0157 is acceptable but only for a short period of time. Driving with this code for an elongated period of time could result in greater engine damage if it is being caused by a lean air-fuel ratio.

Code P0157 Common Diagnosis Mistakes

Replacing the O2 sensor without checking for any exhaust leaks or loose connections.

Tools Needed to Diagnose Code P0157:

• FIXD
• Multimeter
• Fuel pressure gauge
• Spray bottle of water

How to Diagnose and Repair Code P0157:

Difficulty of Diagnosis and Repair – 2 out of 5

1. Visually check the O2 sensor wiring and harness connections for any corrosion in the connections or for any physical damage that might be present.
2. Check for exhaust leaks before the sensor and repair as needed.
3. Check sensor voltage after the vehicle has fully warmed up. You should have between .1-.95 volts. If it is less than this, you most likely have a faulty O2 sensor. To be sure, continue diagnosis.
4. Check fuel pressure and compare it to your vehicle specification. (too low of a fuel pressure can cause the engine to run lean causing O2 sensor to read lean aka low voltage.)
5. Conduct a visual and audible inspection of the vacuum lines and any intake connections to make sure there are no signs of disconnection or outside air leaks. (This includes the intake pipe between the throttle body and MAF)

• Listen for a hissing sound, which can be a sign of a vacuum leak.
• Spray water over intake area and listen for idle rpm stumble. If it goes down, then there is an intake leak. Concentrate the stream on different hoses and gaskets until you find your leak.

Estimated Cost of Repair

For error code P0157, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair.

• Oxygen sensor $200-$300
• Exhaust repair $100-$200 (if welded to repair)
• Fuel Pump $1300-$1700
• Fuel pressure regulator $200-$400
• Vacuum leak $100-$200