P0151 — O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)
Low severityWhat it means
P0151 is stored when the engine control unit sees a fault involving the upstream oxygen sensor on bank 2 (sensor 1). On V-type engines, bank 2 is the cylinder bank opposite cylinder 1; this upstream sensor trims fuel for that bank before the converter. A “low” reading means the signal is stuck near the bottom of its range, which usually points to a short to ground or an internally failed sensor.
Common symptoms
- The live reading sits abnormally low or at zero
- Rough running or higher fuel use
- Check engine light
- Failed emissions test
Likely causes
- Signal wire shorted to ground
- Internally failed sensor pulling the signal low
- Aged or contaminated bank 2 oxygen sensor
- An exhaust leak near the sensor
What to check first
- Compare the live signal against a known-good range and check for a short to ground
- Compare bank 1 and bank 2 sensor behaviour in live data
- Inspect the bank 2 exhaust and sensor wiring
Can you keep driving?
Drivable short-term; like any fuel-control sensor it wastes fuel and stresses the converter, so repair soon.
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