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

What Is Code P0137?

The P0137 trouble code means “O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2).”

It indicates a low-voltage signal in the downstream sensor (rear O2 sensor on Bank 1), which measures the air-fuel ratio from the catalytic converter. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects a voltage output of less than 210 mV (0.21 volts) for over 20 seconds.

Typically, the downstream O2 sensor should produce a steady voltage of about 450 mV (0.45 volts) once the catalytic converter is warmed up. Anything lower means excessive oxygen in the exhaust stream or a problem with the O2 signal circuit.

This problem could be due to damaged wires, high resistance in the wiring (from corrosion or loose connections), or a faulty sensor. It can also result from excessive oxygen in the exhaust stream which can distort the O2 sensor’s signal and severely impact performance.

Common Causes for P0137

Here are possible causes of a P0137 error code: 

• Faulty O2 sensor
• Short circuit in the oxygen sensor circuit due to high voltage
• High resistance or an open circuit in the O2 signal wiring
• Loose electrical connections or a compromised sensor connector 
• Exhaust leak before the downstream O2 sensor
• Plugged catalyst
• Excessively high or low fuel pressure or fuel pump regulator issues
• Engine running lean
• Engine misfires 
• Outdated Engine Control Module software (rare)

Common Symptoms of Code P0137 in Your Vehicle

Here are the signs that may accompany a code P0137: 

1. Loss of engine power: An improper air-fuel mixture from high oxygen levels can cause rough idling or slow acceleration.

2. Exhaust leak and odor: Leaks in the exhaust before the O2 sensor or after the catalytic converter can cause higher emissions and strong smells.

3. Warning lights: The Check Engine Light may flash with other dashboard warnings, such as the traction control light.

4. Higher fuel consumption: A low voltage signal tricks the ECM into adding too much fuel. The extra fuel burns inefficiently, wasting gas and increasing harmful emissions.

Can You Still Drive with P0137 Code?

Yes, you can drive with a DTC P0137, though it’s best not to. The issue is moderately serious, and extended driving can cause:

• Engine failure and damage
• Catalytic converter damage
• Poor fuel mileage
• Failed emission tests

Eventually, it can cause the engine to seize completely, leading to expensive repairs. To avoid this, contact a mechanic ASAP.

P0137 Code Diagnosis: A Step-by-Step Guide

One of the most common P0137 diagnosis mistakes is replacing the sensor without checking for damaged or loose wires, engine issues, or exhaust leaks. To avoid unnecessary repairs and wasted money, it‘s best to have a qualified mechanic diagnose the problem correctly. 

Here are the steps a mechanic would take:

1. Scan the code using an OBD-II scan tool, document the freeze frame data (failure records), and clear the codes to verify the low voltage condition.

2. Monitor the downstream sensor live data and compare it with the upstream O2 sensor voltage data.

3. Measure the oxygen sensor’s voltage output with a multimeter. Downstream sensors should maintain a steady voltage around 0.45V.

4. Check the O2 sensor wiring, harness, and harness connector on the second oxygen sensor circuit for damage or corrosion.

5. Look for an exhaust leak before the rear sensor. They may also examine the vacuum line for a vacuum leak.

6. Check the fuel pressure to see if it’s low using a fuel pressure gauge.

7. Follow other pinpoint tests mentioned in the manufacturer’s manual.

8. Check the O2 sensor for fluid contamination or physical damage, which could be the reason behind the faulty sensor.

Possible Repairs for a P0137 Code

Here’s how a mechanic may resolve a DTC P0137:

1. They will repair or replace a faulty O2 sensor, damaged or corroded wiring, harness, and harness connector. They’ll also address loose connections in the O2 sensor circuit.

2. The mechanic will repair leaks in the exhaust manifold.

3. If a faulty fuel pressure regulator causes the low voltage readings, they’ll replace it since it would mean the O2 sensor is functioning fine.

4. The mechanic will repair the vacuum line if there’s a leak.

5. They’ll replace a faulty Bank 1 sensor 2. If the cause is a restricted or damaged catalytic converter, they’d replace that instead. Sometimes, a broken catalyst damages the rear O2 sensor. In such cases, they’ll replace both.

6. If the earlier steps do not work, they’ll reprogram the ECM. If reprogramming fails, they’ll replace the ECM, though this is rare.

After repairs, the mechanic will re-scan the codes using the scan tool and monitor the Check Engine Light to confirm they’ve resolved the issue.

NOTE: A mechanic will prioritize addressing sensor heater issues or related pending error codes, since they also trigger a P0137 error code.

P0137 Trouble Code Repair Costs

A diagnosis typically costs $75-$150, depending on the mechanic’s labor rate. The final repair cost depends on the parts or work required. 

Here are the estimated repair costs, including parts and labor:

• Oxygen sensor (rear sensor) replacement: $360 to $520
• Exhaust manifold repair (welding): $200 to $350
• Fuel pump replacement: $1,100 to $1,300
• Fuel pressure regulator replacement: $260 to $870
• Vacuum leak repair: $12 to $202
• Catalytic converter replacement: $450 to $4,200
• ECM replacement: $700 to $2,000

O2 Sensor Maintenance Tips

Follow these simple steps to keep the O2 sensor in good shape:

1. Fix exhaust leaks quickly to protect the oxygen sensor and maintain engine efficiency.

2. Use ISO (International Organization for Standardization) and SAE (Society of Automotive Engineers) compliant downstream or upstream sensors.

3. Replace spark plugs and air filters on time to prevent misfires that can damage the sensor.

4. Check gaskets, flanges, and flex pipes regularly for signs of leaks or wear.

5. Avoid running the engine rich for too long, or it will damage the sensor and catalytic converter.

6. Use high-quality fuel and repair oil or coolant leaks promptly to keep the sensor clean.

7. Regularly inspect the downstream O2 sensor wiring and connectors. Since the sensor sits low, road debris can damage it.