Diagnostic trouble code P0137 is a generic OBD-II powertrain fault code. It indicates that the powertrain control module has detected a low voltage condition in the downstream oxygen sensor circuit for bank 1, sensor 2.
Exact vehicle application must be verified before diagnosis. The code identifies an electrical fault in the sensor circuit, but further testing is required to identify the root cause.
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Key Takeaways
- P0137 is a generic OBD-II code indicating a low voltage condition in the bank 1, sensor 2 oxygen sensor circuit.
- Possible causes include damaged wiring, poor electrical connections, an exhaust leak, or a failed downstream oxygen sensor.
- Symptoms often include an illuminated Check Engine Light and potentially failed emissions tests, though drivability issues are rare.
- Diagnosis requires inspecting the sensor circuit wiring, checking for exhaust leaks, and testing the sensor signal and heater circuits.
- Repairs involve fixing damaged wiring, sealing exhaust leaks, or replacing the confirmed failed oxygen sensor.
P0137 Code Description and Implications
P0137 is a generic OBD-II diagnostic trouble code. It indicates that the powertrain control module (PCM) has detected a voltage in the bank 1, sensor 2 oxygen sensor circuit that is lower than the expected operating range.
Bank 1 sensor 2 is the downstream oxygen sensor, located after the catalytic converter. Its primary role is to monitor catalyst efficiency, not to directly control the air-fuel mixture.
A circuit low condition means the module is seeing an unexpectedly low voltage signal, often indicating a short to ground or an open circuit. This requires electrical diagnosis to identify the exact point of failure.
Common Causes of the P0137 Code
Possible causes for a circuit low condition include damaged, chafed, or melted wiring in the bank 1, sensor 2 oxygen sensor circuit that is shorting to ground.
Corroded, loose, or pushed-back pins in the electrical connectors at the sensor or the control module can also disrupt the circuit.
An exhaust leak upstream of or near the downstream sensor can draw in fresh air, causing the sensor to read a persistently low voltage.
A failed downstream oxygen sensor with an internal short or contamination may also trigger this code.
Symptoms Associated With P0137
The most immediate symptom is an illuminated Check Engine Light. Because the downstream sensor primarily monitors the catalytic converter, a P0137 code rarely causes noticeable drivability issues.
The engine will typically idle and accelerate normally. However, the vehicle may fail an emissions inspection due to the illuminated warning light and incomplete monitor readiness.
If an exhaust leak is the root cause, you may also hear a ticking or hissing noise from the exhaust system.
Diagnosing the P0137 Trouble Code
Diagnosis begins by verifying the exact wiring diagram for the specific vehicle to identify the bank 1, sensor 2 circuit path, signal, and heater pins.
Technicians inspect the wiring harness and connectors at the sensor and control module for visible damage, corrosion, or chafing against the hot exhaust.
Using a scan tool, they monitor the live data for the downstream sensor voltage to see if it is stuck low or fluctuating abnormally.
They also inspect the exhaust system for leaks near the sensor and test the sensor signal and heater circuits with a digital multimeter.
Repairing the P0137 Issue
If wiring damage or a short to ground is found, the affected harness section must be repaired, soldered, and properly insulated with high-temperature materials.
If an exhaust leak is confirmed near the sensor, the leaking exhaust component or gasket must be repaired or replaced.
If the sensor fails electrical testing or live data analysis, the confirmed failed downstream oxygen sensor must be replaced.
If all external circuits and the sensor test correctly, follow the manufacturer diagnostic procedure to evaluate the powertrain control module.
Cost Considerations for P0137 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing a downstream oxygen sensor involves standard labor times and moderate parts costs. Repairing an exhaust leak may require welding or replacing exhaust pipe sections.
Prevention Strategies for Future Occurrences
Inspecting exposed exhaust wiring harnesses for chafing, heat damage, or moisture intrusion can help prevent intermittent circuit faults.
Addressing engine misfires or oil consumption issues promptly can help prevent contaminating the oxygen sensors with unburned fuel or ash.
Troubleshooting Tips and Best Practices
Never assume the oxygen sensor has failed just because a circuit code is present. P0137 specifically identifies an electrical fault in the wiring or an exhaust leak causing a false low reading.
Do not confuse the downstream sensor (sensor 2) with the upstream sensor (sensor 1). The upstream sensor controls fuel trim, while the downstream sensor monitors the catalyst.
Check for technical service bulletins related to updated wiring harnesses, revised sensors, or control module software updates for your specific model year and configuration.
More OBD-II Codes
| P0135 | P0138 | P0420 | P0300 |
| P0133 | P0140 | P0430 | P0301 |
| P0132 | P0141 | P0171 | P0302 |
| P0131 | P0150 | P0174 | P0303 |
| P0130 | P0155 | P0170 | P0304 |
| P0136 | P0156 | P0172 | P0305 |
Frequently Asked Questions
Is P0137 a generic or manufacturer-specific code?
Yes. P0137 is a generic OBD-II code, meaning its definition as a bank 1, sensor 2 oxygen sensor circuit low voltage fault is standardized across all vehicle makes and models.
Can I drive my car with a P0137 code?
Yes, in most cases. Because the downstream sensor monitors the catalytic converter and does not directly control fuel delivery, drivability is usually unaffected. However, the vehicle will fail emissions tests.
Will disconnecting the battery clear the P0137 code?
Disconnecting the battery may temporarily clear the code, but it does not repair the underlying electrical short, exhaust leak, or component failure. It also resets readiness monitors.
Can an exhaust leak cause a P0137 code?
Yes. An exhaust leak near the downstream sensor can draw in fresh air, causing the sensor to read a persistently low voltage and triggering the circuit low code.
Does P0137 always mean the oxygen sensor is bad?
No. While a failed sensor is a possible cause, the code can also be triggered by damaged wiring, poor connections, a short to ground, or an exhaust leak.
What Should You Do About the P0137 Code?
Confirm the exact wiring diagram and diagnostic procedure for your specific vehicle application. Because P0137 identifies an electrical circuit fault or a false reading, tracing the sensor circuit and checking for exhaust leaks is mandatory.
Follow the applicable diagnostic steps to test the wiring, connectors, and sensor signals. Once the root cause is confirmed, repair or replace the failed components and verify system operation.
