P0139: O2 Sensor Circuit Slow Response Bank 1 Sensor 2
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - no driveability effect, but the car will not pass an emissions test.
Symptoms
- Check engine light only
- Normal driving feel
- Emissions readiness monitors not completing
Likely causes, most common first
- Downstream sensor aged and responding slowly
- Sensor coated with combustion deposits
- Small exhaust leak near the sensor
- Engine burning oil or coolant, poisoning the sensor
Read P0139 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0139 says the downstream sensor on bank 1 still works but reacts too slowly for the computer's test. Oxygen sensors age gradually - they do not usually fail outright - and slow response is what that ageing looks like in code form.
Before replacing it, consider what may have poisoned it. An engine that burns oil or has leaked coolant into the exhaust coats sensors and converters alike, and a new sensor fitted to an engine with that underlying problem will report the same complaint again within a year.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0139
“I just bought the car and had it 1 week and I was driving to work when the check engine light came on suddenly and car started misfiring. This happened right when I was stopped at a light and turned on my a/c. 3 codes came on which were p0420, p0139, and p2647. I was told I need to reprogram the powertrain control module. I have seen many recalls on here for that same thing but when I put my VIN number in it says 0 recalls for my car. I just really feel it is related to campaign 11v395000”2007 Honda Accord · Jul 2020 · 140,000 mi
“Engine light came on the 29th day of ownership, with odb code p0139. The one o2 sensor was replaced, driving back home after the repair the engine light came back on. Took it back the next day same code p0139, this time they replaced the ecm/pcm computer. After almost two weeks the engine light came back on with the same code. I purchased this car with on 7 miles on it and it's been in the dealership 3 with less than 2k on it. *tr”2020 Jeep Cherokee · Jun 2020 · 1,128 mi
“2002 nissan maxima check engine light came on with p0139 and p1147 codes. Dealer performed a repair under tsb ntb02-051a. This should be a recall, not a tsb. Cost is $480. *nm”2002 Nissan Maxima · Jan 2005 · 77,220 mi
Cars that report P0139 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0139?
Yes - no driveability effect, but the car will not pass an emissions test.
How much does it cost to fix P0139?
Typical US repair costs range from $150 for the simplest fix (downstream oxygen sensor) to $600 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0139. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.