P0137 on a BMW: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to drive — this downstream sensor only monitors the catalytic converter, so a BMW with P0137 can be driven while you arrange the repair.

What P0137 means on a BMW

On a BMW, P0137 means the DME sees low voltage from the bank 1 downstream oxygen sensor, the one behind the catalytic converter. Because this sensor only checks converter efficiency, low voltage usually points to a faulty sensor, damaged wiring, or an exhaust leak — not a fuel problem. On inline-six BMWs, bank 1 is the only bank; on V8s it is the driver's side.

Is P0137 common on BMWs?

P0137 shows up on higher-mileage BMWs as exhaust heat and age take a toll on post-cat sensors and their wiring. Exhaust leaks at corroded pipe joints are also common on older 3 Series and X5s, and a leak before the sensor can drag its voltage down and set the code.

Commonly reported on: 3 Series, 5 Series, X3, X5.

Symptoms

Check engine light on
Usually no change in how it drives
Possible faint exhaust tick from a leak
Slightly worse fuel economy if a leak is present

Common causes

most common: Faulty bank 1 downstream oxygen sensor
common: Exhaust leak before the downstream sensor
common: Damaged or corroded sensor wiring from exhaust heat
less common: Water or contamination in the sensor connector

How to fix it

Fix	DIY?	Typical cost
Replace the bank 1 downstream oxygen sensor	Yes	$80–300
Inspect and repair an exhaust leak near the sensor	Mechanic	$100–350
Repair damaged O2 sensor wiring or connector	Mechanic	$80–250