Oxygen (lambda) sensors

P0139 Rear oxygen sensor responds slowly

By: Diagno editorial team · Updated: 2026-10-15

P0139 means: Rear oxygen sensor responds slowly. The rear oxygen sensor sits after the catalytic converter. OK to drive, but have it checked soon. The repair usually costs about €60–250 in Estonia. The most common cause: sensor is old or faulty. Other possible causes: wire or connector is damaged, exhaust leak.

Is it safe to drive?OK to driveOK to drive, but have it checked soon.

Typical repair cost€60–250parts and labour in Estonia

What it means

The rear oxygen sensor sits after the catalytic converter. The engine computer uses it to check whether the converter is working. The sensor is ageing and reacts slowly.

What could be wrong

1Sensor is old or faulty
2Wire or connector is damaged
3Exhaust leak
4Catalytic converter is worn out

What you can check yourself

Check the sensor wire and connector. The wire often runs under the car and is easily damaged. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

We check the sensor reading with a diagnostic tool
We check for exhaust leaks
We replace the sensor if it is faulty

Standard SAE description: O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

This code usually comes with: Check engine lightSee what the light means →

Want a definite answer?

Bring the car to our workshop in Estonia for diagnostics. We read the fault codes, test the sensors and tell you what is wrong. Repair price depends on the work involved, generally €45 per hour.

Book a diagnostic check

Questions

What does fault code P0139 mean?

Rear oxygen sensor responds slowly. The rear oxygen sensor sits after the catalytic converter. The engine computer uses it to check whether the converter is working. The sensor is ageing and reacts slowly.

Can I drive with code P0139?

OK to drive, but have it checked soon.

How much does it cost to fix P0139?

Roughly €60–250 in Estonia. The price depends on exactly what has failed and on the car.

How is P0139 fixed?

We check the sensor reading with a diagnostic tool. We check for exhaust leaks. We replace the sensor if it is faulty.

Based on AI combined with our hands-on workshop experience and knowledge. This information is general and prices are approximate (Estonian workshop rates). The same code can mean different things on different cars. Only an inspection of the car gives a definite answer.