P0037 Rear oxygen sensor heater: voltage too low

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

P0037 means: Rear oxygen sensor heater: voltage too low. The oxygen (lambda) sensor has a built-in 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: sensor heater element has failed (most common).

What it means

The oxygen (lambda) sensor has a built-in heater so it warms up quickly. If the heater fails, the sensor doesn't work while the engine is cold and fuel consumption may go up. There is a break in the heater wiring or the heater element has failed.

What could be wrong

1. 1Sensor heater element has failed (most common)
2. 2Fuse has blown
3. 3Wire or connector is melted or broken

What you can check yourself

Check the lambda heater fuse in the fuse box. Make sure the sensor wire isn't touching the hot exhaust pipe. You can do the simpler checks yourself.

How we fix it

1. We measure the heater resistance and power supply
2. We replace the fuse or repair the wire
3. We replace the oxygen sensor

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