Faulty, aging or contaminated bank 2 sensor 2 oxygen sensor (OBD-Codes.com says this is the most likely cause if the code returns). Broken, frayed or shorted sensor wiring. Exhaust leak, especially in front of the sensor. Intake air leaks or a faulty MAF sensor (OBD-Codes.com suggests checking these). Engine computer (PCM) failure (listed by RepairPal; not listed by OBD-Codes.com).

Replace the bank 2 sensor 2 oxygen sensor (RepairPal lists oxygen sensor replacement as the common repair). Repair damaged or shorted wiring. Repair an exhaust leak in front of the sensor. Fix any intake air leak or MAF sensor fault found. Repair or reprogram the PCM only after the sensor, wiring and leaks check out.

P0159🌫 Emissions / downstream oxygen sensorUsually OK to drive

P0159: O2 Sensor Circuit Slow Response (Bank 2, Sensor 2) (Meaning, Causes, Fixes)

Q: What does P0159 mean?

P0159 means the oxygen sensor after the catalytic converter on bank 2 (sensor 2) is responding too slowly. The usual causes are an aging or contaminated sensor, damaged wiring, or an exhaust leak, and RepairPal also lists a failed engine computer (PCM) as a less common cause. Bank 2 is the side of a V6 or V8 engine that does not have cylinder 1, and sensor 2 is the downstream oxygen sensor, mounted after the catalytic converter on that side. OBD-Codes.com says the code means the air-fuel ratio is not being adjusted by the oxygen sensor signal or the ECM as expected, or not as often as expected, once the engine is warmed up. RepairPal's description is more general: the PCM has detected a failure of the sensor or of the information it receives from it. OBD-Codes.com calls this the rear passenger-side sensor, but which side bank 2 is on depends on the engine, so go by where cylinder 1 is. Engines with a single bank (most four-cylinders) don't have a bank 2. Exact test criteria vary by manufacturer.

Q: Can I keep driving with P0159?

Usually OK to drive. Get it checked within a reasonable time. RepairPal rates P0159 'Moderate', meaning it isn't usually an immediate safety risk, and OBD-Codes.com says you likely won't notice any drivability problems. Left alone, though, it can cause an emissions test failure, and RepairPal lists reduced engine performance and higher fuel use as symptoms. If the check engine light is flashing, the engine runs very rough, or you smell fuel or see heavy smoke, stop driving and have it looked at, because those point to a bigger problem than this sensor. Exhaust parts get very hot, so let the car cool fully before touching the oxygen sensor.

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0159 means

Bank 2 is the side of a V6 or V8 engine that does not have cylinder 1, and sensor 2 is the downstream oxygen sensor, mounted after the catalytic converter on that side. OBD-Codes.com says the code means the air-fuel ratio is not being adjusted by the oxygen sensor signal or the ECM as expected, or not as often as expected, once the engine is warmed up. RepairPal's description is more general: the PCM has detected a failure of the sensor or of the information it receives from it. OBD-Codes.com calls this the rear passenger-side sensor, but which side bank 2 is on depends on the engine, so go by where cylinder 1 is. Engines with a single bank (most four-cylinders) don't have a bank 2. Exact test criteria vary by manufacturer.

Severity: can I keep driving?

Usually OK to drive

Get it checked within a reasonable time. RepairPal rates P0159 'Moderate', meaning it isn't usually an immediate safety risk, and OBD-Codes.com says you likely won't notice any drivability problems. Left alone, though, it can cause an emissions test failure, and RepairPal lists reduced engine performance and higher fuel use as symptoms. If the check engine light is flashing, the engine runs very rough, or you smell fuel or see heavy smoke, stop driving and have it looked at, because those point to a bigger problem than this sensor. Exhaust parts get very hot, so let the car cool fully before touching the oxygen sensor.

Common symptoms

Check engine light on
Often no noticeable drivability problems (per OBD-Codes.com)
Decreased engine performance (listed by RepairPal)
Increased fuel consumption (listed by RepairPal)
Failed emissions test

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Faulty, aging or contaminated bank 2 sensor 2 oxygen sensor (OBD-Codes.com says this is the most likely cause if the code returns)
Broken, frayed or shorted sensor wiring
Exhaust leak, especially in front of the sensor
Intake air leaks or a faulty MAF sensor (OBD-Codes.com suggests checking these)
Engine computer (PCM) failure (listed by RepairPal; not listed by OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. Fix misfire, fuel trim (such as P0174) or catalytic converter codes such as P0430 first.
OBD-Codes.com suggests the simplest first step is to clear the code and see whether it comes back.
With the exhaust cold, find the bank 2 sensor 2 oxygen sensor just after the catalytic converter on the side without cylinder 1, and check its wiring and connector for damage, fraying, melting or corrosion.
Look and listen for exhaust leaks ahead of the sensor, such as a ticking or puffing sound at a cold start, or soot around joints, flex pipes and gaskets.
Check for intake air leaks and make sure the air filter box and intake hoses are sealed.

Typical fixes

Replace the bank 2 sensor 2 oxygen sensor (RepairPal lists oxygen sensor replacement as the common repair)
Repair damaged or shorted wiring
Repair an exhaust leak in front of the sensor
Fix any intake air leak or MAF sensor fault found
Repair or reprogram the PCM only after the sensor, wiring and leaks check out

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

OBD-Codes.com lists checking the frequency and amplitude of the oxygen sensor signal as an advanced test, which needs a scan tool with live data or a lab scope
The sources differ on symptoms: OBD-Codes.com says you likely won't notice drivability problems, while RepairPal lists decreased engine performance and higher fuel use
The sources also differ on causes: RepairPal includes a PCM failure, which OBD-Codes.com doesn't mention, while OBD-Codes.com adds intake air leaks and the MAF sensor
The code returns after a new sensor, or P0430 or fuel and misfire codes are also present

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0159?

Usually, for a while. RepairPal rates it 'Moderate', and OBD-Codes.com says you likely won't notice drivability problems. Get it diagnosed within a reasonable time, because it can affect fuel use and make you fail an emissions test.

Which oxygen sensor is bank 2 sensor 2?

It is the sensor after the catalytic converter on bank 2, the side of the engine that does not have cylinder 1. Only engines with two banks, such as V6 and V8 engines, have one.

Will replacing the oxygen sensor fix P0159?

Often. OBD-Codes.com says you will likely end up replacing the rear sensor if the code returns after clearing, and RepairPal lists sensor replacement as the common repair. Check the wiring and look for exhaust leaks in front of the sensor first.

What's the difference between P0159 and P0139?

Both are slow-response codes for the sensor after the catalytic converter. P0139 is for bank 1 (the side with cylinder 1), while P0159 is for bank 2. P0153 is the bank 2 sensor before the converter.

Sources

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.