P0051 Oxygen sensor heater: signal or voltage too low (bank 2, sensor 1)

By: Diagno editorial team · Updated: 2026-10-15

P0051 means: Oxygen sensor heater: signal or voltage too low (bank 2, sensor 1). The oxygen sensor has a heater so it warms up quickly. OK to drive, but have it checked soon. The repair usually costs about €60–250 in Estonia. The most common cause: connector loose, damp or corroded.

What it means

The oxygen sensor has a heater so it warms up quickly. If the heater doesn't work, the sensor gives no proper reading on a cold engine and fuel use goes up. The signal voltage is too low. Usually a wire is broken, a connector is loose or a wire is shorted to ground. Bank 2 is the side of a V engine without cylinder 1.

What you may notice

• Engine light on
• Slightly higher fuel consumption
• Usually no change in how the car drives

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire broken or shorted to ground
3. 3Faulty oxygen sensor
4. 4Engine computer fault (rare)

Repair difficulty: Easy

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Check the oxygen sensor heater fuse. Make sure the sensor wire isn't touching the hot exhaust. You can do the simpler checks yourself.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the oxygen sensor

Standard SAE description: HO2S Heater Control Circuit Low (Bank 2 Sensor 1)