Code
P0163
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Circuit Bank 2 Sensor 3 Low Voltage
AI status
Completed
Completed
100%
Causes
- Faulty HO2S (Bank 2 Sensor 3) sensor
- Open or shorted signal wiring between sensor and ECM
- Corroded, loose, or damaged connector or pins at the sensor or ECM
- Poor ground or interrupted 12V/ignition supply to the sensor heater
- Exhaust leak near the sensor causing abnormal readings
- Contamination of the sensor (oil, coolant, silicone, silicone-based sealants)
Symptoms
- Check Engine (MIL) illuminated
- Failed emissions test or readiness monitor incomplete
- Reduced catalytic converter monitoring (downstream sensor fault)
- Possible poor fuel economy or drivability issues in some cases (usually minor for downstream sensors)
- Heater lamp or DTC for heater circuit may also be set if heater supply is affected
What to check
- Read / record freeze frame and all active/pending DTCs with a scan tool
- Verify MIL status and readiness monitors
- Visually inspect sensor harness and connector for damage, corrosion, melting, or exhaust soot
- Check for exhaust leaks near Bank 2 sensor locations
- Use live-data to monitor Bank 2 Sensor 3 voltage and heater status while engine is warm
- Backprobe connector and check reference voltage, signal voltage, and ground continuity to the ECM
Signal parameters
- Oxygen sensor (narrow-band) signal: ~0.1 V (lean) to ~0.9 V (rich). Low-voltage threshold typically
- Downstream sensors often sit near ~0.45 V with smaller swings; sustained
- Heater circuit supply: switched 12 V or battery voltage when commanded (varies by vehicle)
- Heater resistance (typical range, vehicle-specific): ~1–20 ohms; extremely high or open indicates failed heater
- Continuity: signal wire to ECM should be near 0 ohms; open or high resistance is a fault
Diagnostic algorithm
- Verify the code: clear codes, run vehicle to re-test and confirm P0163 returns.
- Capture freeze-frame and live data with engine at normal operating temperature; note Bank 2 Sensor 3 voltage and heater status.
- Visual inspection: trace harness from sensor to ECM; repair any chafing, melted insulation, or connector corrosion.
- Backprobe signal wire at sensor with engine running: measure voltage. If voltage is low (
- With key on engine off, check for heater supply voltage at the sensor connector (should have battery or switched voltage depending on design).
- Measure heater resistance at the sensor; open or infinite resistance = failed heater. Also check for continuity to ECM and for a proper ground.
- Wiggle test harness and connectors while monitoring live data for intermittent drops.
- If wiring and connectors check good but voltage remains low, inspect/verify ECM pin voltages and for driver short to ground. Replace ECM only after exhaustive verification.
- If sensor signal wiring/heater wiring is faulty, repair wiring or connectors. If wiring good and heater or sensor output is bad, replace Bank 2 Sensor 3.
- After repair, clear codes, perform readiness drive cycle and verify no return of the code and proper sensor behavior in live data.
Likely causes
- Broken or chafed signal/ground wire to Bank 2 Sensor 3
- Corroded sensor connector causing high resistance and low voltage
- Failed heater element inside the oxygen sensor
- Sensor contaminated by oil or coolant making it slow/low output
- Open circuit or high-resistance ground in heater/signal circuit
- ECM driver shorted to ground or failed (less common)
Fault status
Status
P0163 — Heated oxygen sensor circuit low voltage detected for Bank 2, Sensor 3. The sensor output or heater circuit is reporting lower-than-expected voltage to the ECM.
Repair difficulty: Medium
Diagnostic time: 0.8-2.0 hours
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