Powertrain, generic · Fuel and air metering

P0157 O2 Sensor Circuit Low Voltage Bank 2 Sensor 2

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The oxygen sensor after the catalytic converter on bank 2 (sensor 2) is a switching sensor (about 0.1–0.9 V) used for converter monitoring and fine mixture trim. Bank 2 exists only on V and boxer engines with a separate downstream sensor per bank. P0157 means the signal stays below the lower limit, the bank 2 counterpart of P0137. GM sets it below 50 mV (two trips), on its 3.0 V6 within 50 s in closed loop; Ford uses its pull-up resistance check and counts both open circuit and short to ground as P0157. 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)

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.

Parts involved

oxygen sensor bank2 sensor2oxygen sensor wiringcatalytic converter

Related codes

P0158P0156P0160P0137P0151P2A04

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