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P0156 – Meaning, Causes, Symptoms, & Fixes

P0156
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What Does Code P0156 Mean?

  • P0156 definition: Oxygen Sensor Circuit Malfunction (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 P0156 code. This DTC can be triggered by an exhaust leak or faulty oxygen sensor and/or wiring.

Your car has oxygen (O2) sensors that measure the amount of oxygen present in your exhaust. Based on the measurements taken, the O2 sensor will fluctuate between a high(rich) and low(lean) voltage reading. Your Engine Control Module (ECM) uses the voltage levels provided by your O2 sensors to regulate your engine’s fuel injector pulse. If you are seeing code P0156, it means that the O2 sensor behind your catalytic converter on bank 2 is malfunctioning.

P0156 Causes

  • Faulty Bank 2 O2 sensor 2
  • Exhaust leak in front of sensor 2
  • Intake leak
  • Corrosion in connecter
  • Frayed or broken wiring

P0156 Symptoms*

  • Check Engine Light
  • Decrease in MPG
  • Increased tailpipe emissions

*No noticeable adverse conditions in some cases

How Do I Fix Code P0156?

With a P0156 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 P0156 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 P0156?

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 P0156 code.

Possible Repair Costs for P0156

When it comes to making repairs associated with the P0156 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)
  • Vacuum leak $100-$200

DIY Steps to Diagnose Code P0156

If you’d like to try to fix code P0161 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 P0156 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 OXYGEN SENSOR(S) LIVE DATA WITH FIXD.

Note if the O2 sensor is rapidly or slowly switching from low to high voltage. This could indicate a faulty O2 sensor.

STEP 4: INSPECT OXYGEN SENSOR WIRING.

Check for any broken or shorted wiring in relation to the O2 sensor. If there is any broken or shorted wiring, make sure to repair or replace it.

STEP 5: INSPECT VACUUM LINES.

Check for any vacuum leaks in the engine or any holes in the exhaust that could lead to air escaping from the engine. Repair any leaks or holes you find.

STEP 5: 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 P0156 diagnosis mistakes

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

Still Need Help Fixing Code P0156?

If you’ve followed the steps above and are still experiencing issues with the oxygen sensor and code P0156, 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.

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.

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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