P0139 Oxygen sensor after the converter - slow response (bank 1, sensor 2)
P0139 means the oxygen sensor after the converter (bank 1, sensor 2) responds too slowly: for example, during engine braking, when the fuel supply is cut, its signal drops too late. The usual cause is an ageing or contaminated sensor, not the converter.
Does restoration help?
Most likely not the catalytic converter
Most likely not: the code points to the sensor or its circuit, not to the converter, and restoring the converter will not fix this fault. If P0420 or P0430 is present as well, we assess the converter only once the sensor and its circuit are in order.
A code shows where to look, but it is not a final diagnosis. We make the decision at the workshop after diagnostics and measurement.
Symptoms
- Check Engine light on; the car usually drives as before.
- As long as the sensor is not working properly, the control unit cannot correctly assess how the converter is working.
- The code soon comes back after clearing until the cause is fixed.
Most common causes
- An ageing sensor.
- Sensor contaminated with oil, coolant or silicone.
- An exhaust leak or damaged wiring.
- If both bank 1 sensors respond slowly - an injector problem is also possible.
Order of checks
What to do
- 1
Read the codes and data
During the computer diagnostic we look at all the codes and the live sensor signal to find out whether the fault is in the sensor, its circuit or somewhere else.
- 2
Check the circuit
Wiring, connector, fuse and heater circuit - the fault may be there rather than in the sensor itself.
- 3
Then the sensor and the converter
If the circuit is in order, the sensor most likely needs replacing. We assess the converter separately - only if P0420 or P0430 is present as well.
FAQ
Questions about P0139
A contaminated or ageing sensor is usually replaced. What matters more is finding where the contamination comes from - oil or coolant damages the converter too.
Not directly. A slow sensor after the converter makes it hard to assess the converter correctly, so if both codes are present, we sort out the sensor first and only then assess the converter.
P0139
Not sure what is wrong with your car?
Tick the symptoms or enter the fault code - in 30 seconds you get a first assessment of whether the part can be restored. If restoring is no longer worth it, we buy the old converter.
Request
Book a check or a job
Leave your contact details - we will get back to you, clarify the situation and agree on a time.
- Phone+371 29 007 007
- Phone+371 28 777 998
- WhatsApp+371 20 099 444
- Emailinfo@autokatalizatori.lv
- AddressJūrkalnes iela 62, A7 bokss, Rīga
