P0137
PowertrainOxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
The bank 1 sensor 2 (rear) oxygen sensor is reporting a voltage stuck low. A healthy rear sensor sits relatively stable around 0.6-0.8V when the catalytic converter is functioning; stuck below 0.2V usually means an open circuit or a failed sensor.
ⓘ Information only. This page provides general educational information about fault code P0137. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0137 mean?
P0137 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2).
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light, often the only symptom
- • Slightly worse fuel economy
- • Generally no drivability impact
- • Sometimes accompanied by P0420 if the cat is also misbehaving
Possible causes
Causes commonly associated with P0137, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed rear sensor, the sensor element has stopped responding (most common at 80,000+ miles)
- 2. Open circuit in sensor wiring (broken signal wire)
- 3. Connector unplugged or corroded
- 4. Exhaust leak ahead of the sensor drawing in air, faking a permanent lean signal
- 5. Damaged catalytic converter not catalysing properly
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Inspect connector first, water ingress and corrosion are common causes
- 2. Check sensor wiring continuity from connector to ECU
- 3. Read live data, rear sensor stuck below 0.2V at idle confirms the symptom
- 4. Inspect the exhaust manifold and cat housing around the rear sensor for cracks or leaks
- 5. If wiring and exhaust are good, the sensor itself is the suspect
Common questions about P0137
Could it be the catalytic converter rather than the sensor? +
Possibly, but check codes alongside. A failed cat usually triggers P0420 (efficiency below threshold) before or alongside P0137. If P0137 appears alone with no cat efficiency code, the sensor is by far the more likely culprit. Cats usually don't fail silently to where they look like a sensor fault.
I have an aftermarket exhaust, related? +
Possibly. Sports cats and de-cat systems sometimes set rear sensor codes because the exhaust gas reaching the rear sensor doesn't have the same characteristics as a stock cat would produce. Some installers fit an oxygen sensor 'spacer' (also called a defouler) to delay the sensor's reading, which clears the code on some makes; results vary and it's a workaround rather than a proper fix.
Is this safe to drive with? +
Yes, drivability is unaffected. The rear sensor is monitoring, not controlling. The downside is the warning light masks anything else that develops and the code fails MOT if the light is on. No urgent safety risk.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →