O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
What it means
The engine computer has found that the bank 2 upstream oxygen sensor signal stays flat after warm-up and does not react to mixture changes. Precise fuel control on that bank stops and the computer uses estimated values; the cause is usually an open circuit, a failed heater or a dead sensor.
Symptoms4
- Check engine light on.
- Higher fuel consumption.
- A heater code such as P0155 or P0050 may appear with it.
- Failed emissions test.
Possible causes5
- Open signal or ground wire, or an unplugged connector.
- Faulty sensor heater or the fuse feeding it.
- Completely failed sensor.
- Wiring melted by contact with the exhaust behind the engine.
- Engine computer fault (rare).
How to diagnose5
- Start with any heater codes and fix them first.
- Watch the sensor signal after warm-up and compare it with bank 1; if bank 1 switches and bank 2 stays flat, the problem is in the bank 2 circuit.
- Inspect the connector and the wiring route behind the engine for melting or breaks.
- Check wiring continuity between the sensor and computer using the manufacturer wiring diagram.
- If the circuit is sound, replace the sensor.
How to fix5
- Reconnect or clean the connector.
- Repair melted or broken wiring and route it away from the exhaust.
- Repair the heater circuit, or replace the fuse after finding why it blew.
- Replace the bank 2 upstream oxygen sensor if it is proven to give no signal.
- Clear the codes and confirm the signal switches once warm.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
An unplugged connector or broken wire costs little, while a new sensor brings the cost to the upper end, especially when access is difficult.
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
Does this code affect only half the engine?
Yes. Only bank 2 loses precise mixture control, while bank 1 keeps working with its own sensor.
Why does bank 2 sensor wiring sometimes melt?
On some engines it runs close to the exhaust manifold behind the engine, so if it comes loose from its clips it touches hot parts.
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What was wrong? (optional)
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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