Powertrain, generic · Fuel and air metering

P0137 O2 Sensor Circuit Low Voltage Bank 1 Sensor 2

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The oxygen sensor after the catalytic converter on bank 1 (sensor 2) is a switching sensor (about 0.1–0.9 V) used for converter monitoring and fine mixture trim. P0137 means the signal stays below the lower limit. Documented limits: GM below 40–60 mV (two trips); Ford switches in a pull-up and reads open above 1 MΩ (20 kΩ from 2020) or short to ground below 10 Ω, within 10 s. Subaru uses the code as a functional test instead: the sensor never reaches 550 mV within 200 s after fuel cut-off, i.e. it behaves as if permanently lean – so a real exhaust leak can also trigger it there. When it fails, the control module stops the downstream trim and cannot evaluate the converter; there is no limp mode.

Likely causes

Signal wire shorted to ground or melted against the exhaust
Sensor faulty (cracked element, thermal shock from water)
Signal circuit open (counts as low on Ford)
Exhaust leak ahead of the sensor (lean reading)
Signal and ground wires swapped after a repair

Symptoms

  • Check engine light on (usually after two drive cycles)
  • Catalyst monitor readiness not set
  • Usually no noticeable change in driving

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–250
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Look for exhaust leaks upstream of the sensor
  2. Check fuel trims
  3. Inspect wiring

Parts involved

oxygen sensor bank1 sensor2oxygen sensor wiringcatalytic converter

Related codes

P0138P0140P0157P0143P0131P2A01

References: law.cornell.edu, gsi.ext.gm.com, newtonnet.co.uk, saabwisonline.com.