Code
P0151
GWM
P — Powertrain
- Oxygen sensor circuit low voltage (bank 2, sensor 1)
Views:
UK: 3
EN: 8
RU: 0
AI status
Completed
Completed
100%
Causes
- Faulty bank 2 sensor 1 (upstream O2 sensor)
- Wiring shorted to ground or open circuit in sensor signal circuit
- Corroded/loose connector or poor pin contact
- Failed sensor heater circuit or open heater element
- Exhaust leak upstream of the sensor causing lean readings
- Vacuum leak or fuel delivery issue causing real lean condition
Symptoms
- Check Engine Light (MIL) illuminated, code P0151 stored
- Poor fuel economy (if ECU runs richer or incorrect trims)
- Rough idle or hesitation under some conditions
- Failed emissions test (high NOx or HC)
- Possible difficulty starting or surging if sensor heater not working
What to check
- Read freeze‑frame and live data with a scan tool; inspect short‑term and long‑term fuel trims for lean condition on bank 2
- Visually inspect O2 sensor connector and wiring for damage, corrosion, chafing, or disconnection
- Backprobe the sensor signal wire with engine running and compare voltage to expected range (see signal_params)
- Check sensor heater power and ground with key ON and engine OFF; measure heater resistance and supply voltage
- Perform smoke or vacuum test to rule out intake/exhaust leaks upstream of the sensor
- Wiggle test wiring while monitoring live data to check for intermittent faults
Signal parameters
- Typical narrowband zirconia sensor signal: ~0.0–1.0 V (approx). Low voltage indicates lean (~0.1 V or less is considered low)
- Normal upstream (sensor 1) should switch between ~0.1–0.9 V under closed‑loop when working correctly; a steady low value indicates a problem
- Heater circuit: supply typically battery voltage with key ON; heater resistance often in the low single‑digit to tens of ohms (manufacturer specific)
- Note: exact voltages/resistances vary by vehicle/sensor — use manufacturer specs when available
Diagnostic algorithm
- Confirm code and inspect freeze‑frame data to note conditions when fault occurred
- Scan for additional codes that could point to fuel or ignition issues
- Visually inspect sensor and harness at bank 2 sensor 1 for physical damage, corrosion, or disconnected pins
- Backprobe the sensor signal wire with engine running: verify voltage is not stuck low. If low, check for short to ground between sensor connector and chassis
- With key ON engine OFF, check for 12 V (or switched battery) at heater supply terminal and continuity to ground for heater. Measure heater resistance; compare to spec. Replace sensor if heater open or out of spec
- If heater and wiring are good but signal remains low, check for exhaust or intake vacuum leaks and fuel pressure/flow problems that could cause genuine lean condition
- If wiring checks fail to show open/short, perform a resistance/continuity check from PCM connector to sensor connector to identify internal wiring shorts/opens
- Repair or replace damaged wiring or sensor as required, clear codes and perform a drive cycle to confirm repair; if code returns, consider PCM or deeper electrical diagnostics
Likely causes
- Damaged/contaminated O2 sensor
- Broken or chafed signal wire to sensor with short to chassis ground
- Disconnected/corroded connector at the sensor
- Open heater element (sensor heater not warming sensor)
- Upstream exhaust leak producing false low voltage readings
Fault status
Status
Oxygen sensor circuit low voltage detected — Bank 2 Sensor 1 (upstream).
Repair difficulty: Medium
Diagnostic time: 1.0-2.0 hours
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