Motor Vehicle Expert
OBD oxygen sensor fault guide

P0137 Code Meaning UK

P0137 means “O2 Sensor Circuit Low Voltage Bank 1 Sensor 2”. In plain English, the engine computer is seeing a low voltage signal from the downstream oxygen sensor after the catalytic converter. This can be caused by a faulty sensor, damaged wiring, poor connector contact, exhaust leak, low voltage, sensor contamination or a catalytic converter monitoring issue.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Mechanic-style O2 sensor advice
Quick answer Diagnosis steps Fault Codes Hub
✓ Downstream O2 low voltage explained ✓ UK repair cost guide ✓ MOT emissions advice ✓ Heavy internal linking included
Quick answer Meaning Symptoms Causes Can you drive? Repair costs Diagnosis MOT impact Related guides FAQs
Quick answer

What does P0137 mean?

P0137 means the ECU has detected a low voltage signal from the oxygen sensor circuit for bank 1 sensor 2. This is normally the downstream oxygen sensor fitted after the catalytic converter.

The downstream oxygen sensor mainly monitors catalytic converter performance. A low voltage fault can be caused by the sensor itself, but wiring damage, connector corrosion, exhaust leaks, low voltage and catalyst-related issues should also be checked.

Most common area

Downstream oxygen sensor, wiring, connector, exhaust leak or low voltage signal fault.

Main risk

Emissions monitoring may be unreliable and the engine warning light may stay on.

Best first check

Check live downstream O2 data, wiring, connector condition and exhaust leaks.

Code meaning

P0137 — O2 sensor circuit low voltage bank 1 sensor 2

Bank 1 is the side of the engine containing cylinder 1. Sensor 2 means the oxygen sensor after the catalytic converter. This downstream sensor checks how well the catalytic converter is working.

P0137 is stored when the ECU sees a downstream oxygen sensor signal that is lower than expected. This may be a genuine low signal, a wiring problem, poor connector contact or a sensor that is no longer responding properly.

Symptoms

Common symptoms of a P0137 code

P0137 may not always make the car drive badly because bank 1 sensor 2 mainly monitors catalyst performance.

Engine management light

A steady engine warning light is the most common symptom.

Emissions warning

Some cars may show emissions or catalyst-related warnings.

Normal driving feel

The car may still drive normally even with the code stored.

Poor fuel economy

Some vehicles may adapt differently when oxygen sensor data is unreliable.

Exhaust leak noise

A leak around the sensor or catalytic converter area can affect readings.

Related catalyst codes

P0137 may appear with P0136, P0141, P0420 or other oxygen sensor faults.

Common causes

What causes P0137?

P0137 can be caused by the downstream sensor, its wiring or a fault affecting exhaust oxygen readings.

Sensor

Faulty downstream oxygen sensor

The sensor may be stuck low, slow, contaminated or internally faulty.

Electrical

Damaged sensor wiring

Wiring near the exhaust can suffer heat damage, rubbing, corrosion or road impact.

Connector

Poor connector contact

Loose pins, water ingress or corrosion can interrupt the downstream oxygen sensor signal.

Exhaust

Exhaust leak near the sensor

A leak around the catalytic converter or sensor area can alter oxygen readings.

Catalyst

Catalytic converter issue

A weak or contaminated catalyst can create abnormal downstream sensor behaviour.

Voltage

Low voltage or ECU signal issue

Poor ground, low supply voltage or ECU signal interpretation problems can cause circuit faults.

Safe to drive?

Can you drive with P0137?

Short careful driving may be possible if the car runs normally and there are no serious symptoms. However, P0137 should not be ignored because it can affect emissions monitoring and may be linked to exhaust or catalytic converter problems.

✅ Lower risk: steady engine light only, normal running and no smoke or fuel smell.

⚠️ Medium risk: repeated downstream O2 sensor codes, exhaust leak noise or P0420 catalyst code.

🚫 Higher risk: flashing engine light, misfire, smoke, strong fuel smell or catalyst overheating smell.

Can You Drive With Engine Light? Engine Light Guide
Catalyst warning

Check catalyst and exhaust faults properly

Because bank 1 sensor 2 sits after the catalytic converter, P0137 should be taken seriously if it appears with P0420 or emissions problems.

Do not replace the catalytic converter until the downstream sensor, wiring, exhaust leaks and upstream fuel mixture issues have been checked.

P0420 Catalyst Code P0136 Sensor 2 Circuit
UK repair costs

Typical UK repair costs for P0137

Costs depend on sensor access, wiring condition, exhaust condition and whether catalyst-related faults are also present.

Diagnostic scan and live data

Typical range: £40–£120.

Downstream oxygen sensor replacement

Typical range: £100–£350+.

Wiring or connector repair

Typical range: £60–£300+.

Exhaust leak repair

Typical range: £80–£400+.

O2 heater circuit repair

Typical range: £60–£250+.

Catalyst diagnosis

Typical range: £80–£180+ before any catalytic converter repair.

Repair Costs Guide UK
Diagnosis flow

How to diagnose P0137 properly

✅ Scan all stored, pending and permanent codes.

✅ Record freeze-frame data before clearing anything.

✅ Check whether P0137 appears with P0136, P0141, P0420 or upstream oxygen sensor codes.

✅ Inspect downstream oxygen sensor wiring near the exhaust.

✅ Check connector condition, corrosion and pin fit.

✅ Read live downstream O2 sensor voltage.

✅ Compare upstream and downstream oxygen sensor behaviour.

✅ Inspect for exhaust leaks around the catalytic converter and sensor area.

✅ Check heater circuit operation if P0141 is also present.

✅ Confirm sensor or circuit fault before replacing the sensor.

Real experience

What I would check first

On a real P0137 fault, I would start with the downstream oxygen sensor wiring and connector. These sensors are often exposed to heat, water and road debris, so circuit faults are common.

Then I would check live sensor voltage. If the sensor is stuck low even when conditions change, and the wiring checks out, the sensor becomes a stronger suspect.

P0136 Sensor 2 Circuit P0141 Sensor 2 Heater P0420 Catalyst
MOT impact

Will P0137 fail an MOT?

P0137 itself is not normally what directly fails an MOT. The concern is what it causes. If it triggers an emissions-related engine warning light, high emissions, catalyst problems, smoke, misfire or poor running, it can become an MOT issue.

⚠️ Higher risk: engine warning light, emissions failure, smoke, misfire or catalyst issue.

⚠️ Medium risk: repeated downstream O2 code, exhaust leak or P0420 catalyst code.

✅ Lower risk: repaired fault, no warning light and normal emissions behaviour.

Engine Light MOT Guide Emissions MOT Guide
Used car buying advice

P0137 on a car you want to buy

If a used car has P0137 stored, check for oxygen sensor history, exhaust leaks, catalyst codes, emissions problems, fuel smell and wiring repairs around the exhaust.

A downstream oxygen sensor can be a manageable repair, but if the fault is linked to a weak catalytic converter or exhaust damage, the cost can rise.

Used Car Buying Guides Inspection Checklist
Frequently asked questions

FAQs about P0137

Common questions about P0137 oxygen sensor low voltage bank 1 sensor 2, safe driving, repair costs and MOT impact.

What does code P0137 mean?

P0137 means the ECU has detected low voltage from the oxygen sensor circuit for bank 1 sensor 2.

Can I drive with P0137?

Short careful driving may be possible if the car runs normally, but emissions and catalyst monitoring can be affected.

What is bank 1 sensor 2?

Bank 1 sensor 2 is normally the downstream oxygen sensor fitted after the catalytic converter.

Can P0137 mean a bad catalytic converter?

Sometimes. P0137 can be sensor or wiring related, but it may appear with catalyst-related faults such as P0420.

Will P0137 fail an MOT?

It can contribute to an MOT issue if it causes an engine warning light, emissions failure, smoke, misfire or catalyst problems.

Should I replace the oxygen sensor first?

Not before checking live data, wiring, connector condition, exhaust leaks, heater operation and related catalyst codes.

About this guide

Written for practical UK fault finding

Motor Vehicle Expert explains diagnostic trouble codes in clear, mechanic-style language for UK drivers. This P0137 guide is designed to help you understand downstream oxygen sensor low voltage faults, likely causes, safe driving advice, repair costs and MOT implications before replacing parts.

Fault codes should always be treated as a diagnostic starting point. P0137 can involve the downstream oxygen sensor, wiring, connectors, exhaust leaks, heater circuits, voltage supply and catalytic converter performance, so proper testing is better than guessing.