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P0157 – Meaning, Causes, Symptoms, & Fixes

P0157
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What Does Code P0157 Mean?

  • P0157 definition: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2)
  • Issue Severity: MODERATE– Extended driving with this code can cause internal engine damage.
  • Repair Urgency: Get this code fixed as soon as possible.
  • Diagnosis: It is important to complete the entire diagnostic process when diagnosing the P0157 code. This DTC is usually triggered by a faulty oxygen sensor, but exhaust leaks, low fuel pressure, and a lean air/fuel ratio can also be the cause.

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.

P0157 Causes

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

P0157 Symptoms

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

*No adverse conditions in some cases

How Do I Fix Code P0157?

With a P0157 code, the first step is to get it properly diagnosed to figure out what is causing the malfunction in the oxygen sensor system. Using the live data function of the FIXD sensor and app allows you to read and analyze engine data to properly diagnose a P0157 code.

If the sensors are all reading correctly and you’re not comfortable further diagnosing this issue at home, we recommend finding a RepairPal-certified shop to pinpoint the problem and give an accurate estimate for repairs.

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

> Find a RepairPal Certified Shop Near You

How Much Does It Cost to Fix Code P0157?

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0157 code.

Possible Repair Costs for P0157

When it comes to making repairs associated with the P0157 code, 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

DIY Steps to Diagnose Code P0157

If you’d like to try to fix code P0157 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Complete diagnosis may require some specialized equipment beyond what the FIXD Sensor can provide, but the biggest challenge for this repair is that internal engine issues could be the root cause of this code. As such, this diagnosis and repair should not be attempted by beginner DIYers.

DIY difficulty level: Beginner

This repair can be attempted by beginner DIYers.

Tools/parts needed (our top picks from Amazon):

STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.

Scan your vehicle to verify P0157 is the only code present. If other codes are present, they must be addressed first.

STEP 2: INSPECT O2 SENSORS AND WIRING.

Visually check the electrical connections, wire harness, and metal tabs in terminals for any damages. If any damage is found, replace the oxygen sensor.

STEP 3: CHECK FOR EXHAUST OR VACUUM LEAKS.

Check for exhaust leaks before the sensor and repair as needed.

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 including 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.

STEP 4: CHECK O2 SENSOR VOLTAGE WITH VOLTMETER.

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.

STEP 5: CHECK FUEL PRESSURE.

Check fuel pressure and compare it to your vehicle specification. Low of a fuel pressure can cause the engine to run lean causing O2 sensor to read lean, aka low voltage.

STEP 6: CONSULT A PROFESSIONAL.

If at this point the vehicle is still setting the same code, you may have a more serious problem with your car’s oxygen sensor system, and you should bring the vehicle to a certified shop to have further diagnostic work performed.

Common P0157 diagnosis mistakes

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

Still Need Help Fixing Code P0157?

If you’ve followed the steps above and are still experiencing issues with the oxygen sensor system and code P0157, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.

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Jeffrey-Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

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We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.

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About the Author

Jeffrey N. Ross

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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