Technical Explanation
The diagnostic trouble code P0137 is registered when the Engine Control Module (ECM) detects a low voltage condition in the oxygen (O2) sensor circuit for Bank 1, Sensor 2. This is commonly referred to as:
Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
Decoding the P0137 Code: What Does It Really Mean?
P0137 is a generic powertrain code, meaning it’s applicable across all vehicles equipped with OBD-II systems. However, specific repair procedures can differ between car manufacturers and models.
This code is very similar to P0136, and it specifically points to the second oxygen sensor on Bank 1. Bank 1 refers to the side of the engine containing cylinder number 1. Sensor 2 is the downstream oxygen sensor, located after the catalytic converter.
The P0137 code is triggered when the ECM observes that the voltage output from the Bank 1, Sensor 2 oxygen sensor remains consistently low for an extended period, typically exceeding 2 minutes.
The ECM interprets this persistently low voltage as an indication that the sensor is not detecting sufficient oxygen in the exhaust stream after the catalytic converter. The sensor, located downstream of the catalytic converter, is meant to monitor the converter’s efficiency by measuring the oxygen storage capacity. While Sensor 2 is less active than the upstream sensor (Sensor 1), a consistently inactive or low voltage signal will trigger the P0137 code and illuminate the Malfunction Indicator Lamp (MIL) – also known as the Check Engine Light.
Common Symptoms of a P0137 Error
Often, the most noticeable symptom of a P0137 code is the Check Engine Light illuminating on your dashboard. In many cases, there may be no other immediately apparent symptoms affecting the vehicle’s drivability. However, in some instances, you might experience:
- No noticeable symptoms: Just the Check Engine Light.
- Slight decrease in fuel economy: Due to potential issues affecting engine management.
- Possible failed emissions test: Due to the oxygen sensor malfunction.
Potential Causes of a P0137 Code
Several factors can lead to a P0137 error code. Here’s a breakdown of the common culprits:
- Faulty Oxygen Sensor (Bank 1, Sensor 2): The most frequent cause. The sensor itself may be degraded or malfunctioning internally.
- Exhaust Leak Near Sensor 2: Leaks in the exhaust system before or near the downstream oxygen sensor can introduce extra oxygen, causing the sensor to read low voltage.
- Plugged or Failing Catalytic Converter: A restricted or inefficient catalytic converter can affect exhaust flow and sensor readings.
- Wiring Issues in the O2 Sensor Circuit:
- Short to Voltage on O2 Signal Circuit: An electrical short can incorrectly bias the sensor signal.
- High Resistance or Open Circuit on O2 Signal Circuit: Damaged wiring, corroded connectors, or an open circuit can disrupt the sensor signal.
- Engine Running Condition Issues:
- Engine Running Very Rich or Lean: Imbalances in the air-fuel mixture can affect oxygen sensor readings.
- Engine Misfire: Misfires can introduce unburnt fuel and oxygen into the exhaust, potentially confusing the downstream sensor.
- Fuel Pressure Problems (High or Low): Incorrect fuel pressure can lead to rich or lean conditions, impacting sensor readings.
- PCM/ECM Malfunction (Less Likely): In rare cases, a fault within the Powertrain Control Module (PCM) or Engine Control Module (ECM) could incorrectly trigger the P0137 code.
Troubleshooting and Possible Solutions for P0137
Addressing a P0137 code requires systematic diagnosis. Here are the common solutions, progressing from the most likely to less frequent fixes:
- Oxygen Sensor Replacement (Bank 1, Sensor 2): Given its frequency as the cause, replacing the Bank 1, Sensor 2 oxygen sensor is often the first step. Ensure you use a quality replacement sensor.
- Exhaust Leak Inspection and Repair: Thoroughly inspect the exhaust system, especially around and before the Bank 1, Sensor 2 location. Repair any detected leaks.
- Catalytic Converter Check: Evaluate the catalytic converter for blockage or failure. This may require professional diagnosis and potentially replacement.
- O2 Sensor Circuit Wiring Inspection and Repair: Carefully examine the wiring harness and connectors for Bank 1, Sensor 2. Look for signs of damage, corrosion, or loose connections. Repair any shorts, opens, or high resistance issues in the wiring.
- Engine Performance Diagnostics: If wiring and sensor are ruled out, investigate potential engine running condition problems. Check for:
- Misfires: Perform a cylinder misfire test.
- Fuel Pressure: Test fuel pressure to ensure it’s within specification.
- Air-Fuel Ratio Imbalance: Use a scan tool to monitor live data and check for excessively rich or lean conditions.
- PCM/ECM Diagnosis (Advanced): If all other possibilities are exhausted, PCM/ECM malfunction could be considered, but this is rare and requires advanced diagnostic tools and expertise.
Important Note: Always consult your vehicle’s repair manual for specific diagnostic procedures and component locations.
Further Assistance with P0137
For more in-depth assistance with the P0137 trouble code, we encourage you to post your question in our FREE car repair forums. Our community of experienced mechanics and automotive enthusiasts can offer further guidance and insights to help you resolve your issue.
Disclaimer: This information is intended for informational purposes only and should not be considered professional repair advice. We are not liable for any actions taken on your vehicle based on this information. All content is copyright protected.
