P0159

O2 Sensor Circuit Slow Response (Bank 2 Sensor 2)

Car Fault Codes Emissions & exhaust

Can you still drive? Yes, normally

Who can fix it? DIY with some experience

Typical repair time 30 minutes – 1.5 hours

Typical cost SAR 150 to 900

What it means

The engine computer has found that the bank 2 downstream oxygen sensor is slow to react to mixture changes, such as switching to a lean reading during fuel cut. The usual cause is an aged sensor; engine performance is normally unaffected, but monitoring of that bank's catalytic converter stops.

Symptoms4

Check engine light on.
Usually no noticeable driving symptoms.
Bank 2 catalytic converter self-test does not complete.
Failed emissions test.

Possible causes5

Aged bank 2 downstream oxygen sensor.
Sensor contaminated by oil, coolant or additives.
Exhaust leak near the sensor.
Weak sensor heater.
Corroded or loose connector.

How to diagnose5

Watch how long the sensor signal takes to switch when lifting off and then accelerating, and compare it with the bank 1 downstream sensor.
Review the sensor self-test results on the scan tool if available.
Check the exhaust for leaks near the sensor.
Make sure there is no heater code such as P0161.
Inspect the connector and its terminals.

How to fix5

Repair any exhaust leak.
Clean the connector or repair the wiring.
Fix any oil burning or coolant leak before fitting a new sensor.
Replace the bank 2 downstream oxygen sensor.
Clear the codes and drive until the self-test completes.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is usually the downstream sensor plus removal labor, and may rise if it is rusted in or an exhaust leak needs repair.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Can I delay the repair?

A short delay is usually fine since it rarely harms the engine, but a lit check engine light can hide new faults, and the car will fail an emissions test.

Does this code mean the converter is bad?

No. It concerns the sensor's own speed, but it must be fixed so the computer can judge the converter correctly.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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