P0137: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

Concerned about the P0137 code popping up and not sure what it means?

Let’s give you a quick rundown of what to expect. 

  • P0137 Definition: Oxygen Sensor Circuit Low Voltage (Bank 1, Sensor 2.)
  • Code type: Generic – P0137 indicates the same problem whether you’re having a Chevy, Toyota, or Honda, etc.
  • Can I drive with the P0137 code? Yes, in the short run. However, extended driving periods may cause engine damage.
  • Easy to fix? Beginner to intermediate level.
  • Cost: $20 – $95 (common.)

In this article, I will go over what the code means, possible causes, solutions, and repair costs. 

Let’s get started!


Table Of Contents


What Does The P0137 Code Mean?

The P0137 is triggered when the downstream O2 sensor (bank 1) voltage is lower than 0.21V for longer than 2 minutes. In many cases, it can be because your downstream O2 sensor is faulty.

Downstream oxygen sensors (located after the catalytic converter) monitor the conditions of the catalytic converter. 

The more air in the exhaust gas (after passing the cats), the lower the downstream O2 sensor’s output voltage. 

Because the catalytic converter already processed the exhaust gas, the oxygen level is stable. Therefore, a normal working downstream O2 sensor stays around 0.45 volts. 

For some reason, the sensor may detect an abnormally high percentage of oxygen in the exhaust gas (or it thinks so.) This leads to a drop in the sensor’s voltage. And when it’s below 0.21v, P0137 is set.

P0137 meaning, causes, and solutions

P0137 Causes Identification: Quick View

The most common cause of P0137 is a faulty downstream oxygen sensor. However, there may be other reasons.

To make the information more digestible, here is a table with the code combinations, their causes, and solutions.

Codes combinationsCausesSolution
P0137 only (no symptom);
P0137 + P0420
Bad downstream O2 sensor  
Faulty O2 sensor’s circuit
Replace downstream O2 sensor 
Fix the short or open circuit
P0137 + noisy exhaustExhaust leak near downstream O2 sensorApply epoxy bond (small leak)/welding (large leak)
P0137 + P0141Bad downstream O2 sensor Replace downstream O2 sensor 
P0137 + P0171;
P0137 + P0157
Vacuum leak
Lazy upstream O2 sensor
Smoke test & Seal vacuum leak
Replace upstream O2 sensor
P0137 + P0138Bad PCMReplace PCM

Note: The causes for each code combination are the most common ones. There can be some uncommon issues hidden under those codes. 


P0137 Causes, Symptoms, and How to fix

Depending on the underlying problem, there may be different symptoms to look out for. 

However, there is one common symptom that remains the same, and that is an illuminated check engine light.

Let’s explore the different causes of the P0137 error code and any unique symptoms you may experience.

Causes #1: Bad Downstream O2 Sensor

Downstream O2 sensor location

A faulty downstream O2 sensor would report false info to the PCM, which would think there is something wrong with the catalytic converter.

If this is the case, P0137 may appear alone or come with other codes like P0420, and P0141. 

A bad downstream O2 sensor does not result in any symptoms with your car’s performance. This is because downstream sensors are not used to adjust the air-fuel ratio (like upstream.)

Check the O2 sensor with a multimeter. If this fails, replace it.

Causes #2: Short Or Open In Downstream O2 Sensor Wiring

Sometimes, the problem is not the downstream sensor itself. 

After making sure the O2 sensor is ok, check its wiring harness for any short, high resistant, or open.

Again, this cause will not lead to any symptoms.

bad downstream o2 sensor wiring harness

Causes #3: Exhaust Leak Near Downstream O2 Sensor

When the exhaust gas is pushed out of the system, it forms a pulse. The front end of the pulse has a high pressure while the negative pressure is behind. 

When there is a leak, some of the gas in the front end of the pulse escapes. However, the low pressure at the end of the pulse sucks the air in.

The changes in the exhaust gases cause an inaccurate reading on the downstream O2 sensor. 

The most obvious symptom of an exhaust leak is the buzz or hum sounds when the engine is running. You can rev the car intermittently to hear the sound more clearly. 

how to test exhaust leak near the downstream o2 sensor
Spray soapy water on the area near the downstream O2 sensor. If you see bubbles, that’s an exhaust leak.

After finding the leak, you would need to repair it by applying epoxy to seal a small leak or performing welding for a larger one.

Causes #4: Lean Condition (Bank 1)

If your engine is running lean (too much air), the exhaust gas will contain more oxygen than usual. When the catalytic can not handle all of this, some of the oxygen is still left in the exhaust gas after passing the cats.

As mentioned above, an abnormally high percentage of air will decrease downstream O2 sensors voltage, triggering P0137. 

There are many reasons for the lean condition. However, vacuum leaks and lazy upstream O2 sensors (in this case, the bank 1 sensor) are the most common causes.

Vacuum leak symptoms: 

  • Hissing sounds
  • Rough idle
  • Often stalls when stopping
  • Long-term fuel trim (ltft1)>10% 
high ltft bank 1

Lazy upstream O2 sensors symptom: 

  • The sensor’s output voltage slightly fluctuates above .45v (below image)
lazy o2 sensor output voltage chart causing lean conditions

First, conduct a smoke test to make sure there is no leak in the intake system. 

If there are no leaks, then the problem could be in the upstream O2 sensor. Replacing it with a new one should fix the issue. 

Causes #5: Bad PCM (Rare)

PCM location

Bad PCM is a rare case and it should be your last conclusion. 

If your car throws a combination of P0137 and the P0138 (low voltage and high voltage on one downstream O2 sensor,) this can be the cause. 

Depending on the make and model, the replacement costs of a PCM may vary. But it will not be cheap! 

I suggest heading to a local mechanic for replacing the PCM as it’s a complicated process. 


How Much Does It Cost To Fix The Code P0137?

The most common solution to the P0137 error code is replacing the downstream O2 sensor, which can cost between $20 and $95. 

The table below will help break down repair costs (DIY and mechanic) according to the different solutions.

The Estimated Repair Cost Of P0137

SolutionsRepair cost
Replace O2 sensorDIY: $20 – $95
Mechanic: $100 – $450
Repair O2 sensor circuit DIY: $10 – $20
Mechanic: $130 – $140
Repair exhaust leakDIY: $20- $50
Mechanic: $130 – $190
Replace PCMDIY: Not recommended
Mechanic: $1,000 to $3,000

Note: The data in this table is collected in May 2022. The actual price depends on many factors, such as your car’s make and year, mechanic’s rate, time, market price, etc. 


You ask, I answer

Thank you for sticking with me to the end.

Although a P0137 fault code is not dangerous to drive, having the annoying CEL disappear with a few bucks is a no-brainer.   

If you are still feeling confused or have any questions about P0137 or any other related codes, please do not hesitate to comment below. I’ll try my best to help you out. 

See ya!

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