P0133 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Mercedes with P0133 usually still drives well, but fuel economy drops a little until the sensor is replaced.

What P0133 means on a Mercedes-Benz

On a Mercedes-Benz, P0133 means the bank 1 upstream oxygen sensor is responding too slowly to changes in the exhaust. The engine computer uses this sensor to keep the fuel mixture balanced.

Is P0133 common on Mercedes-Benzs?

P0133 is common on Mercedes models like the C-Class, E-Class, and ML at higher mileage. The upstream sensor wears with age, and oil leaks that contaminate the sensor or a small exhaust leak are frequent contributing causes.

Commonly reported on: C-Class, E-Class, ML, GL.

Symptoms

Check engine light on
Worse fuel economy
Rough idle or hesitation
Failed emissions test

Common causes

most common: Aging upstream oxygen sensor (bank 1, sensor 1)
common: Exhaust leak before the sensor
common: Oil contamination of the sensor
less common: Wiring or connector damage

How to fix it

Fix	DIY?	Typical cost
Inspect the exhaust system for leaks near the sensor	Yes	$50–200
Replace the upstream O2 sensor	Yes	$100–280
Fix any oil leaks that could contaminate the new sensor	Mechanic	$150–400