O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

What it means

The engine computer has found that the downstream oxygen sensor signal on bank 1 stays flat after warm-up, even during acceleration and fuel cut. This usually means an open circuit, an unheated sensor or a dead sensor; engine performance is normally unaffected.

Related codes: P0136P0141P0036P0137P0160

Symptoms4

• Check engine light on.
• Engine usually runs normally.
• A downstream heater code may appear with it.
• Failed emissions test.

Possible causes5

• Open signal or ground wire, or a disconnected connector under the car.
• Faulty sensor heater or the fuse feeding it.
• Completely failed sensor.
• Connector terminals corroded by water and salt.
• Engine computer fault (rare).

How to diagnose5

1. Check for heater codes such as P0141 or P0036 and fix them first.
2. Watch the signal after warm-up during acceleration and when lifting off; if it does not move at all, the sensor is dead or its circuit is open.
3. Check the connector under the car is tight and free of water.
4. Check continuity of the signal and ground wires using the manufacturer wiring diagram.
5. If the circuit and heater are fine, replace the sensor.

How to fix5

1. Reconnect or clean the connector.
2. Repair the broken wire and secure it away from the exhaust.
3. Repair the heater circuit, or replace a blown fuse after finding why it blew.
4. Replace the downstream oxygen sensor if it is proven to give no signal.
5. Clear the codes and drive until the sensor test completes.

A loose connector or broken wire costs little, while replacing the sensor pushes the cost to the upper end.

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