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

P0159 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0159 and illuminates the check engine light.

If your vehicle has triggered P0159, you may notice one or more of these symptoms:

• Check engine light illuminated
• Slight reduction in fuel economy, only on engines that use this sensor to fine-tune the mixture
• No noticeable driveability symptoms
• Possible failed emissions test
• May appear with P0430 if the bank 2 converter is also fading, or cause a false P0430

Here are the most common causes of P0159:

Generally yes, for short-term driving. Safe to drive short term. A slow downstream sensor makes the engine computer's check of the bank 2 catalytic converter unreliable, so a developing converter problem may be masked or a healthy one wrongly flagged. Plan a repair within a few weeks.

Follow these steps to pinpoint the root cause of P0159:

1. Confirm which sensor the code means before buying parts: Bank 2 is the cylinder bank that does not contain cylinder 1, and Sensor 2 is the one after the catalytic converter. Check the cylinder numbering for your engine in the service information, because the side of the car bank 2 sits on is not the same on every engine
2. Read freeze frame data and look for companion codes. P0430 or P0156 point to a converter or sensor cluster issue on bank 2; P0139 stored as well means both downstream sensors are slow, which suggests contamination affecting both banks, such as oil or coolant getting into the exhaust
3. Inspect the bank 2 exhaust between the catalytic converter and the downstream sensor for leaks that could distort the gas sample
4. Inspect the Bank 2 Sensor 2 connector and wiring for corrosion, heat damage or partial open circuits
5. Graph both downstream sensor voltages during a steady cruise and then a lift-off fuel cut. A healthy sensor drops toward 0V almost at once when fuel is cut; a sensor that drifts down slowly, or clearly lags the bank 1 downstream sensor, is aged
6. Substitute a known-good sensor. Response time is the only definitive test, so if the new sensor responds correctly, the original was worn out

Repair costs for P0159 vary depending on the root cause and your vehicle. Here are typical estimates:

P0159 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

These codes are often seen alongside P0159 or indicate related issues: