How do I fix code P0137?

The P0137 code indicates the downstream oxygen sensor (Bank 1 Sensor 2) is reporting a consistently low voltage. In most cars, this points to a faulty sensor or an issue in the wiring, connectors, or exhaust system. Replacing the sensor or repairing wiring typically resolves the problem, but other causes—like exhaust leaks or catalytic converter issues—may also be involved.

What P0137 means

P0137 is an OBD-II diagnostic code that signals a problem with the circuit for Bank 1 Sensor 2, the oxygen sensor located after the catalytic converter. The sensor output is used by the engine control module (ECM) to monitor exhaust gas composition. A persistently low voltage reading from this sensor can trigger a check engine light and may affect fuel efficiency and emissions control. The exact voltage range varies by vehicle, but a sensor that remains in a low state under typical driving conditions is considered faulty or out of specification.

Common causes

Several issues can produce a P0137 warning. The most likely ones are listed below; addressing these in order from simplest to more involved fixes often yields the best results.

• Faulty downstream O2 sensor (Bank 1 Sensor 2) itself



• Exhaust leaks upstream or around the sensor or before/around the sensor that skew readings


• Problems with the oxygen sensor heater circuit (preventing the sensor from warming up properly)


• Catalytic converter inefficiency or failure affecting downstream readings


• ECU/PCM fault or an incorrect calibration

Any of these can cause a persistent low voltage reading on Bank 1 Sensor 2, so a systematic check is important before replacing parts.

Diagnostic steps

To confirm the fault and avoid unnecessary part replacement, follow these diagnostic steps. The list below outlines a practical approach used by many technicians.

1. Use an OBD-II scanner to verify the code and review freeze-frame data. Check whether Bank 1 Sensor 1 (upstream) is operating normally while Sensor 2 remains consistently low.


2. Inspect the Bank 1 Sensor 2 harness and connector for signs of damage, corrosion, oil contamination, or loose connections. Gently wiggle the connector to see if the reading fluctuates.


3. Check for exhaust leaks around the sensor location, including gaskets and flanges, as leaks can affect sensor readings.


4. Test the downstream sensor’s heater circuit if your vehicle’s manual provides heater resistance specs. A faulty heater can prevent proper operation, especially on cold starts.


5. If you have access to a multimeter or oscilloscope, measure the sensor’s heater resistance and sensor signal voltage with the engine at operating temperature. Compare results to the manufacturer’s specifications.


6. Consider swapping Bank 1 Sensor 2 with a known-good sensor (or swapping sensors between banks if possible) to see if the fault follows the sensor.


7. Inspect the catalytic converter’s health if sensor readings remain abnormal after sensor replacement and wiring fixes. A severely degraded cat can affect downstream sensor behavior and trigger related codes (e.g., P0420).


8. Clear the codes and perform a road test to confirm whether P0137 returns or if other codes appear.

After performing these checks, you’ll have a clearer picture of whether the issue is a faulty sensor, a wiring problem, an exhaust/leak issue, or something deeper in the exhaust aftertreatment system.

Fix options

Based on the diagnostic results, one or more of the following fixes may be appropriate. The goal is to restore proper downstream sensor readings and emission-system function.

• Replace Bank 1 Sensor 2 (downstream O2 sensor) with a new unit that matches the vehicle specifications


• Repair or replace damaged wiring or connectors to Bank 1 Sensor 2, and ensure a solid ground and clean connections


• Repair exhaust leaks around the sensor location or upstream that could distort readings


• If the sensor heater is defective, replace or repair the heater circuit as recommended by the vehicle’s service guide


• Evaluate catalytic converter health if readings persist abnormally after sensor/wiring fixes; consider cat replacement only if diagnostics justify it (e.g., poor catalyst efficiency tests)


• Reset the engine computer after repairs and take a test drive to confirm that the code does not return

In most cases, replacing the faulty downstream O2 sensor or fixing wiring is sufficient. If the problem persists after these steps, more extensive diagnostics of the exhaust aftertreatment system may be required.

What to expect after repair

Once the faulty component is replaced or the wiring is repaired, the vehicle should show normal downstream O2 sensor readings on live data, and the check engine light should stay off if no other faults are present. It may take a short drive for the ECM to relearn fuel trim and stabilise. If the code reappears, recheck the sensor, harness, and any related systems, and consider professional diagnostic help.

Preventive tips

To minimize the chance of P0137 returning, follow these best practices:

• Use quality O2 sensors from reputable brands and avoid aftermarket parts that don’t meet OEM specs


• Keep the exhaust system in good condition and fix leaks promptly


• Regularly inspect wiring and connectors for signs of wear or damage, especially in exposed or hot engine areas


• Follow your vehicle’s maintenance schedule for emissions-related components

Proactive maintenance can help prevent downstream sensor faults and keep the emissions system functioning as designed.

Summary

Code P0137 usually means Bank 1 Sensor 2 is delivering a low voltage signal. The typical path to a fix is to inspect and replace the downstream O2 sensor if needed, repair wiring or connectors, and check for exhaust leaks or catalyst issues. Diagnostic steps should confirm whether the problem is the sensor itself, the wiring, or the exhaust system, before committing to component replacements. If in doubt, seek a qualified technician to ensure proper diagnosis and compliance with emissions standards.