Code
P0146
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Circuit Insufficient Activity Bank 1 Sensor 3
Views:
UK: 7
EN: 20
RU: 16
AI status
Completed
Completed
100%
Causes
- Failed or degraded oxygen sensor (sensor 3)
- Open, short, or high resistance in signal or heater circuit
- Faulty sensor connector or poor pin contact/corrosion
- Blown fuse or relay feeding sensor heater circuit
- Exhaust leak affecting sensor readings
- Contaminated sensor (oil, coolant, silicone, fuel additives)
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Failed emissions test
- Reduced fuel economy (possible)
- Poor drivability rarely shown directly (usually downstream sensor related)
- Stored freeze frame data showing conditions when fault set
What to check
- Read and record all stored DTCs and freeze frame data with a scan tool
- Verify oxygen sensors are at operating temperature during testing (warm engine)
- Compare live data: Bank 1 Sensor 1 (upstream) vs Sensor 3 (downstream)
- Check for obvious exhaust leaks, damaged wiring, or connector corrosion
- Inspect and wiggle harness/connectors while watching live data for intermittent changes
- Check heater circuit supply (battery voltage with key ON) and ground
Signal parameters
- Typical zirconia HO2S voltage range: ~0.1 V (lean) to ~0.9 V (rich)
- Upstream (bank1 sensor1) should switch frequently when closed-loop (~1 Hz or faster once warmed)
- Downstream (bank1 sensor3) normally shows less switching; should not be completely inactive or flatline
- Heater supply: ~12 V with key ON (when configured) and current typically 0.3–2 A depending on sensor
- Heater resistance typical range (varies by sensor): roughly 2–20 Ω (consult OEM spec)
Diagnostic algorithm
- Verify code and capture freeze frame with a scan tool; note engine temp, load, RPM, fuel trims.
- Warm engine to normal operating temperature. Monitor live voltage for Bank1 Sensor1 and Sensor3.
- Observe downstream (Sensor3) behavior: if voltage is flatline (stuck high/low or ~0.45 V no switching), record values.
- Inspect sensor connector and wiring for damage, corrosion, or loose pins. Repair as needed.
- With engine off, disconnect sensor and measure heater resistance between heater pins; compare to spec. Check for short to ground or battery on signal pin.
- With key ON (engine off) check for battery voltage at heater feed (if applicable) and good ground return.
- Backprobe signal wire with engine warm and observe voltage. Wiggle harness to check for intermittent faults.
- Check for exhaust leaks ahead of the sensor and evaluate catalytic converter condition (temperature differential test or backpressure test) if downstream readings remain abnormal.
- If wiring and power/ground are good but sensor output is incorrect, replace Bank1 Sensor3 with OEM or equivalent and clear codes.
- After repair, erase codes and perform a drive cycle to verify the fault does not return. If it does, consider PCM diagnostics or internal faults.
Likely causes
- Sensor 3 heater not powered (open fuse/relay or wiring open)
- Wiring short to battery or ground on signal or heater circuit
- Connector corrosion or bent terminals at sensor harness
- Aging sensor with slow/no switching output
- Exhaust leak upstream of the sensor causing incorrect readings
- Catalyst inefficiency producing abnormal downstream voltages
Fault status
Status
Insufficient activity detected from Heated Oxygen Sensor Bank 1 Sensor 3. PCM/ECM expected switching or signal amplitude from the downstream oxygen sensor but observed low/no activity. Possible causes include failed sensor, heater or wiring fault, contamination, exhaust leak, or catalyst issue. Further testing required to isolate root cause.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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