O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

What it means

The engine computer has seen the bank 2 downstream oxygen sensor voltage stay unusually low, even under acceleration that should raise it. The most common cause is outside air reaching the sensor through an exhaust leak, followed by an electrical short or a failed sensor.

Related codes: P0156P0158P2272P0430P0137

Symptoms4

• Check engine light on.
• Engine usually runs normally.
• Puffing or ticking from the exhaust when there is a leak.
• Failed emissions test.

Possible causes5

• Exhaust leak near or ahead of the bank 2 downstream sensor, such as a failed joint or gasket.
• Signal wire shorted to ground.
• Failed bank 2 downstream oxygen sensor.
• A real lean mixture on bank 2 for a long period.
• Engine computer fault (rare).

How to diagnose5

1. Check the bank 2 exhaust joints and gaskets between the catalytic converter and the sensor.
2. Watch the sensor signal during hard acceleration; the voltage should rise if the sensor is good and there is no leak.
3. Unplug the connector and check the signal wire for a short to ground.
4. Review bank 2 fuel trims to rule out a real lean mixture.
5. Compare the reading with the bank 1 downstream sensor.

How to fix5

1. Repair the exhaust leak or replace the failed gasket.
2. Repair the wire shorted to ground.
3. Fix any lean cause on bank 2.
4. Replace the downstream sensor if its voltage does not rise under acceleration and the circuit is sound.
5. Clear the codes and drive until the self-test completes.

Repair cost

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

An exhaust joint or wiring repair keeps the cost low, while a new sensor takes it 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