O2 Sensor Circuit (Bank 2 Sensor 1)
What it means
This code appears on engines with two banks, such as V6 and V8 engines, and means the engine computer found an abnormal signal from the upstream oxygen sensor on the bank that does not contain cylinder 1. This sensor controls the mixture for half the engine, so that bank may run a less accurate mixture.
Symptoms4
- Check engine light on.
- Higher fuel consumption.
- Occasionally a slightly uneven idle.
- Failed emissions test.
Possible causes6
- Failed or contaminated bank 2 upstream oxygen sensor.
- Damaged wiring or connector; this sensor's wiring often runs near the exhaust at the back of the engine.
- Leak in the bank 2 exhaust manifold ahead of the sensor.
- Sensor heater fault.
- Bank 1 and bank 2 sensor connectors swapped during earlier service.
- Engine computer fault (rare).
How to diagnose5
- Confirm which side is bank 2 on your engine per the manufacturer; it is the bank opposite cylinder 1.
- Compare the bank 2 sensor signal with the bank 1 sensor on a scan tool; the healthy bank gives a useful reference.
- Inspect the connector and wiring along their route, and confirm each sensor is plugged into its correct connector.
- Check the bank 2 exhaust manifold for cracks or a leaking gasket.
- Make sure there is no heater code such as P0155.
How to fix4
- Repair the connector or wiring, and swap the sensor connectors back if they were reversed.
- Repair any exhaust leak ahead of the sensor.
- Replace the bank 2 upstream oxygen sensor if it is proven faulty.
- Clear the codes, drive until the self-test completes, and confirm the code does not return.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
A connector or wiring repair keeps the cost low; the upper end comes with a new sensor, and labor may rise because the bank 2 sensor is sometimes hard to reach behind the engine.
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
Where is bank 2 on my engine?
It is the bank opposite the one with cylinder 1, and its side differs between makers, so check the manufacturer information before removing any sensor.
Could the code appear because a sensor was recently replaced?
Yes. If the new sensor was fitted with the bank connectors reversed, codes like this appear, so check the connections.
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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