| DTC Data Sheet | |
| System | Powertrain |
| Standard | ISO/SAE Controlled |
| Fault type | Circuit Low | Location: Bank 1, Sensor 2 |
| Official meaning | O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 |
DTC P0137 is an ISO/SAE controlled powertrain code that indicates the engine control module (ECM/PCM) has detected a low-voltage condition in the oxygen (O2) sensor circuit for Bank 1 Sensor 2. Bank 1 refers to the engine bank that contains cylinder #1, and Sensor 2 identifies the downstream (post-catalyst) O2 sensor located after the catalytic converter. Because this sensor is used primarily for catalyst monitoring rather than primary fuel control on most systems, the first sign is often an illuminated malfunction indicator lamp (MIL). Even when the vehicle seems to run normally, this circuit-low fault can prevent emissions monitors from completing and can lead to inspection failures until the underlying electrical, sensor, or exhaust-related issue is corrected.
Look up your vehicle's recalls, specs & safety ratings — free VIN decoder with NHTSA data
P0137 Quick Answer
P0137 – O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 means the ECM/PCM is seeing the Bank 1 Sensor 2 O2 sensor signal stay too low. Start by confirming the correct downstream sensor location, then inspect the connector and wiring near the exhaust for damage or poor pin fit, and verify the signal circuit is not shorted to ground and is electrically intact.
What Does P0137 Mean?
P0137 – O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 is set when the ECM/PCM detects a low-voltage condition on the O2 sensor signal circuit for the downstream O2 sensor on Bank 1. In other words, the controller expects Bank 1 Sensor 2 voltage to be within a certain range during specific operating conditions, but it observes the circuit voltage remaining lower than the acceptable threshold for long enough to meet the diagnostic criteria.
This is a circuit-low fault: the diagnostic emphasis is on the electrical signal being low (for example, a short-to-ground, high resistance, poor terminal contact, or an open affecting the signal path) rather than assuming the sensor element itself has failed. Bank 1 is the side of the engine with cylinder #1; on engines with only one bank, Bank 1 still applies.
Theory of Operation
Bank 1 Sensor 2 is the downstream O2 sensor located after the catalytic converter. The ECM/PCM uses this sensor primarily to monitor catalyst function by observing oxygen storage and release behavior. Compared with the upstream sensor (Sensor 1), the downstream sensor signal typically changes more slowly and with less switching activity when the catalyst is operating properly.
P0137 is triggered when the ECM/PCM interprets the Bank 1 Sensor 2 signal circuit as being stuck or held at a low voltage. A true circuit-low condition can be produced by a signal wire shorted to ground, excessive resistance in the signal/return path, connector corrosion or poor terminal tension, or a sensor that cannot generate normal voltage due to operating conditions. Because the DTC definition is specifically “circuit low,” the diagnostic process should prioritize verifying circuit integrity and proper electrical conditions at the sensor and at the ECM/PCM input.
Symptoms
- Malfunction indicator lamp (MIL) illuminated
- O2 sensor and/or catalyst readiness monitors may not complete
- Failed emissions inspection due to stored code or incomplete monitors
- Scan tool data showing Bank 1 Sensor 2 voltage consistently low or not responding as expected
- Possible minor drivability changes depending on vehicle strategy (not guaranteed)
Common Causes
- Bank 1 Sensor 2 signal circuit shorted to ground
- Open circuit or high resistance in the Bank 1 Sensor 2 signal wiring
- Corrosion, water intrusion, damaged terminals, or poor pin fit at the Bank 1 Sensor 2 connector
- Damaged harness routing near the exhaust (melted insulation, pinched wires, chafing)
- Exhaust leak near the downstream sensor location that can influence sensor output and keep voltage low
- Bank 1 Sensor 2 O2 sensor fault after circuit checks verify wiring integrity
- ECM/PCM input circuit issue (uncommon) after all external circuit checks are proven good
Diagnosis Steps
Tools: scan tool with live data and freeze-frame, digital volt-ohm meter (DVOM), appropriate wiring diagram/connector views for the vehicle, and back-probing or terminal testing tools. Use safe lifting/support equipment if under-vehicle inspection is required.
- Confirm DTC P0137 is present (stored and/or pending) and record freeze-frame data. Note engine coolant temperature, RPM, vehicle speed, fuel system status, and battery voltage at the time the code set.
- Verify sensor identification and location: Bank 1 Sensor 2 is the downstream O2 sensor after the catalytic converter on the bank containing cylinder #1. Confirm you are diagnosing the correct sensor and connector.
- Visually inspect the Bank 1 Sensor 2 harness and connector. Look for melted wiring, contact with exhaust components, pulled or stretched wires, damaged conduit, or signs of impact.
- Inspect the connector condition closely. Check for bent pins, corrosion, water intrusion, loose terminal fit, or evidence the connector is not fully seated or locked.
- Using the scan tool, observe Bank 1 Sensor 2 live data (voltage) at idle and during a brief steady RPM hold. Note whether the value remains abnormally low and whether it shows any response to changing conditions.
- Perform an electrical check for a short-to-ground on the Bank 1 Sensor 2 signal circuit using the wiring diagram. With the connector disconnected as appropriate, verify the signal circuit is not unintentionally grounded.
- Check for opens/high resistance in the signal circuit between the sensor connector and the ECM/PCM (as applicable). Perform continuity and resistance checks per service information and confirm terminals are mechanically sound.
- Inspect for exhaust leaks at or near the downstream sensor bung, gasket joints, and nearby flanges. Repair leaks that could introduce outside air and affect downstream sensor readings.
- If circuit integrity and connector condition are confirmed good, evaluate the sensor itself by confirming the signal can rise from low voltage under conditions that should change O2 content, while ensuring testing methods follow service information and safety practices.
- After repairs, clear codes and complete a verification drive cycle to confirm P0137 does not return and that relevant readiness monitors can complete.
Professional tip: Treat P0137 as a circuit-low problem first. Before replacing Bank 1 Sensor 2, prove the signal circuit is not being pulled down by a short-to-ground, corrosion, or a damaged harness section near heat sources; intermittent low-voltage faults often occur only when the wiring is hot, vibrating, or under tension.
Possible Fixes
- Repair or replace damaged wiring/conduit for the Bank 1 Sensor 2 circuit (especially heat-damaged sections near the exhaust)
- Clean, dry, and correct connector pin/terminal issues (corrosion removal, terminal tension repair, proper seating/locking)
- Repair exhaust leaks near Bank 1 Sensor 2
- Replace Bank 1 Sensor 2 O2 sensor only after confirming the circuit is not shorted/ खुले and connector integrity is verified
- If verified by pinpoint testing, repair the ECM/PCM input circuit concern (uncommon and should be confirmed with service procedures)
Can I Still Drive With P0137?
In many cases, the vehicle will remain drivable with P0137 – O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 because the downstream sensor is primarily used for catalyst monitoring. However, driving with the code present can prevent emissions monitors from completing and can lead to inspection failure. More importantly, if the low voltage is caused by wiring damage near the exhaust, the condition may worsen with heat and vibration. If additional symptoms appear (such as severe running issues or exhaust concerns), diagnose and repair the underlying circuit-low cause promptly.
How Serious Is This Code?
P0137 is typically an emissions and diagnostics concern rather than an immediate safety issue, but it should not be ignored. Because the code indicates a low-voltage condition in the downstream O2 sensor circuit, it can disrupt catalyst monitoring and keep the vehicle from meeting readiness requirements. If the root cause is a damaged harness or connector, continued operation may lead to further wiring deterioration. Addressing the circuit-low condition in a timely manner helps restore proper monitoring and prevents secondary electrical problems.
Common Misdiagnoses
A frequent misdiagnosis is replacing the downstream O2 sensor without confirming a true circuit-low cause such as a short-to-ground, high resistance, or connector terminal issues. Another mistake is confusing sensor positions and testing Bank 1 Sensor 1 instead of Bank 1 Sensor 2. Overlooking harness damage near hot exhaust components or failing to check for nearby exhaust leaks can also lead to repeated code returns because the underlying low-voltage condition remains unresolved.
Most Likely Fix
The most likely fix for P0137 – O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 is to correct the electrical cause of the low-voltage signal: repair damaged wiring near the exhaust, restore proper connector terminal contact, and eliminate any short-to-ground or high-resistance condition in the Bank 1 Sensor 2 signal circuit. Replace Bank 1 Sensor 2 only after these circuit checks confirm the wiring and connector are not pulling the signal low.
Repair Costs
Repair cost depends on whether the confirmed root cause is a sensor, wiring, connector issue, or control module problem. Verify the fault electrically before replacing parts.
| Repair Type | Estimated Cost |
|---|---|
| Basic DIY inspection | $0 – $50 |
| Professional diagnosis | $100 – $180 |
| Sensor / wiring / connector repair | $80 – $400+ |
| PCM / ECM replacement (if required) | $300 – $1500+ |
Brand-Specific Guides for P0137
Manufacturer-specific diagnostic procedures with factory data and pin-level details for vehicles where this code commonly sets:
Key Takeaways
- P0137 is an ISO/SAE controlled powertrain code for O2 Sensor Circuit Low Voltage Bank 1 Sensor 2.
- Bank 1 Sensor 2 is the downstream (post-catalyst) O2 sensor on the bank containing cylinder #1.
- The diagnostic priority is circuit integrity: shorts to ground, opens, high resistance, and connector terminal problems.
- Exhaust leaks near the downstream sensor can contribute to persistently low readings and must be ruled out.
- After repairs, clear the DTC and confirm readiness monitors can complete without the code returning.
FAQ
What is the official meaning of P0137?
The official meaning of P0137 is: O2 Sensor Circuit Low Voltage Bank 1 Sensor 2.
Which O2 sensor does P0137 refer to?
P0137 refers to Bank 1 Sensor 2, the downstream O2 sensor located after the catalytic converter on the engine bank that contains cylinder #1.
Does P0137 mean the O2 sensor is definitely bad?
No. P0137 is a circuit-low code, so the low voltage may be caused by wiring damage, a short-to-ground, poor connector terminal contact, or an open/high-resistance condition. The sensor should be considered after circuit checks confirm the wiring and connector are good.
What should I check first for P0137?
Start by confirming you are working with Bank 1 Sensor 2, then inspect the connector and harness near the exhaust for melting, chafing, corrosion, or loose terminals. After the visual inspection, test the signal circuit for a short-to-ground and check for opens/high resistance using the proper wiring diagram.
Will P0137 cause a failed emissions test?
Yes, it. An illuminated MIL and stored P0137 will typically fail an emissions inspection, and the downstream O2/catalyst monitors may not complete until the circuit-low condition is repaired and a verification drive cycle is completed.