Motor Vehicle Expert
OBD oxygen sensor fault guide

P0136 Code Meaning UK

P0136 means “O2 Sensor Circuit Malfunction Bank 1 Sensor 2”. In plain English, the engine computer is seeing a problem with the downstream oxygen sensor circuit after the catalytic converter. This sensor mainly monitors catalyst performance, so the fault may involve the sensor, wiring, connector, exhaust leak, sensor contamination or catalytic converter condition.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Mechanic-style O2 sensor advice
Quick answer Diagnosis steps Fault Codes Hub
✓ Downstream O2 fault 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 P0136 mean?

P0136 means the ECU has detected a problem with the oxygen sensor circuit for bank 1 sensor 2. This is normally the downstream oxygen sensor fitted after the catalytic converter.

The downstream sensor does not usually control fuelling as strongly as the upstream sensor. Its main job is to monitor catalytic converter performance. A P0136 code can still affect emissions monitoring and may appear with catalyst-related codes such as P0420.

Most common area

Downstream oxygen sensor, wiring, connector, exhaust leak or catalyst monitoring fault.

Main risk

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

Best first check

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

Code meaning

P0136 — O2 sensor circuit malfunction 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 sensor checks how well the catalytic converter is cleaning the exhaust gases.

P0136 is stored when the ECU sees an abnormal signal, missing signal or circuit problem from the downstream oxygen sensor.

Symptoms

Common symptoms of a P0136 code

P0136 may not always make the car feel different, but it can keep the engine light on and affect emissions monitoring.

Engine management light

A steady engine warning light is the most common symptom.

Emissions fault warning

Some cars may display emissions system or catalyst-related warnings.

Normal driving feel

Many cars still drive normally because sensor 2 mainly monitors the catalyst.

Poor fuel economy

Some vehicles may use substitute values or adapt differently when O2 data is unreliable.

Exhaust smell

If the fault is linked to catalyst or mixture problems, exhaust smell may be stronger.

Related catalyst codes

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

Common causes

What causes P0136?

P0136 can be caused by the downstream sensor, its circuit or a fault affecting exhaust/catalyst readings.

Sensor

Faulty downstream oxygen sensor

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

Electrical

Damaged wiring

Oxygen sensor wiring sits near heat, exhaust movement and road debris.

Connector

Poor connector contact

Corrosion, loose pins or water ingress can interrupt the sensor signal.

Exhaust

Exhaust leak near the sensor

Leaks around the catalytic converter or sensor area can affect oxygen readings.

Catalyst

Catalytic converter issue

A weak catalyst can create downstream oxygen sensor behaviour that looks abnormal.

Voltage

Low voltage or ECU signal fault

Poor sensor supply, ground or ECU signal interpretation can trigger circuit faults.

Safe to drive?

Can you drive with P0136?

Short careful driving may be possible if the car runs normally and there are no serious symptoms. However, P0136 should not be ignored because it can affect emissions monitoring and may hide or accompany catalyst problems.

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

⚠️ Medium risk: repeated O2 sensor codes, exhaust leak, poor economy or 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-related codes carefully

Because bank 1 sensor 2 monitors the catalytic converter, P0136 should be taken seriously if it appears with P0420 or emissions problems.

Do not replace the catalytic converter without checking the downstream sensor, wiring, exhaust leaks and upstream mixture faults first.

P0420 Catalyst Code P0130 Upstream O2
UK repair costs

Typical UK repair costs for P0136

Costs depend on sensor access, wiring condition, exhaust condition and whether a catalyst fault is 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 P0136 properly

✅ Scan all stored, pending and permanent codes.

✅ Record freeze-frame data before clearing anything.

✅ Check whether P0136 appears with P0141, P0420, P0130 or fuel-trim codes.

✅ Inspect downstream oxygen sensor wiring near the exhaust.

✅ Check connector condition, corrosion and pin fit.

✅ Read live downstream O2 sensor data.

✅ Compare upstream and downstream O2 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 P0136 fault, I would first inspect the downstream oxygen sensor wiring and connector. These sensors live underneath the vehicle where heat, water, salt and road debris can cause problems.

Then I would compare upstream and downstream oxygen sensor live data. If sensor 2 is flat, erratic or not believable, the circuit needs checking before replacing the sensor.

P0141 Sensor 2 Heater P0420 Catalyst P0134 No Activity
MOT impact

Will P0136 fail an MOT?

P0136 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

P0136 on a car you want to buy

If a used car has P0136 stored, check for exhaust leaks, catalyst codes, oxygen sensor history, emissions problems, fuel smell and poor repairs around the exhaust wiring.

A downstream sensor can be a manageable repair, but if the code is linked to a tired catalytic converter, the repair can become more expensive.

Used Car Buying Guides Inspection Checklist
Frequently asked questions

FAQs about P0136

Common questions about P0136 oxygen sensor circuit bank 1 sensor 2, safe driving, repair costs and MOT impact.

What does code P0136 mean?

P0136 means the ECU has detected a malfunction in the oxygen sensor circuit for bank 1 sensor 2.

Can I drive with P0136?

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 P0136 mean a bad catalytic converter?

Sometimes. P0136 can be sensor or wiring related, but it may appear with catalyst-related faults such as P0420.

Will P0136 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 P0136 guide is designed to help you understand downstream oxygen sensor circuit 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. P0136 can involve the downstream oxygen sensor, wiring, connectors, exhaust leaks, heater circuits and catalytic converter performance, so proper testing is better than guessing.