Code
P0161
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Heater Performance Bank 2 Sensor 2
AI status
Completed
Completed
100%
Causes
- Open or short in the heater power or ground circuit for Bank 2 Sensor 2
- Failed oxygen sensor heater element
- Blown heater fuse or fusible link
- Poor or corroded connector/terminal (water ingress, corrosion, heat damage)
- High circuit resistance from damaged wiring or poor ground
- Faulty ECM heater driver (rare)
Symptoms
- Check Engine Light / MIL illuminated
- Possible reduced fuel economy or emissions test failure
- Longer closed-loop warm-up time (poor fuel trim control until sensor is hot)
- Sometimes rough idle or drivability issues if sensor stays cold
What to check
- Read freeze frame and related DTCs with a scan tool; note engine temperature at fault
- Visual inspection of sensor, connector, and wiring for damage, heat or corrosion
- Check relevant fuses and relays for heater circuit
- Backprobe sensor connector to verify heater supply voltage with key on/engine running
- Measure heater element resistance at the sensor (spec range provided below)
- Perform wiggle test on harness while monitoring live data / heater voltage
Signal parameters
- Heater element resistance: typically about 2–20 ohms (varies by sensor). An open (infinite) or very high resistance indicates failed heater
- Heater supply voltage: approximately battery voltage (~11–14 V) when the ECM commands heater ON (dependent on vehicle and key/run conditions)
- Heater current: can be >1 A depending on sensor design; verify against manufacturer spec if available
- ECM reports heater circuit fault when commanded heater current or voltage is out of expected range or not present
Diagnostic algorithm
- Verify DTC and capture freeze frame data. Note related codes (especially other O2 sensor or heater circuit codes).
- Perform a visual inspection of the Bank 2 Sensor 2 connector and wiring for chafing, heat damage, corrosion, or water entry.
- Check fuses/relays for the oxygen sensor heater circuit. Replace any blown components and retest.
- With connector disconnected, measure heater element resistance across the sensor heater pins. Compare to expected range (manufacturer spec).
- With key ON/engine running and sensor reconnected, backprobe the heater power terminal to confirm battery voltage when the ECM commands heater ON. Also verify a good chassis or engine ground on the ground side of the heater circuit.
- If no voltage at the connector but fuse is good, trace wiring back to find open/short/loose connection or test the feed/ground for continuity. Repair or replace wiring/connector as needed.
- If wiring, power and ground are good but heater element is open or out-of-spec, replace the oxygen sensor (Bank 2 Sensor 2).
- If new sensor plugged in and fault persists, suspect ECM heater driver fault — verify with manufacturer procedures before ECM replacement.
- Clear codes, perform a warm-up/drive cycle and verify the code does not return.
Likely causes
- Failed heater element in the HO2S (most common)
- Open wiring or connector fault between the sensor and ECM
- Blown fuse or relay supplying the heater circuit
- High-resistance ground or corroded connector causing insufficient heater current
Fault status
Status
Heater circuit performance fault detected for Bank 2, Sensor 2 oxygen sensor (heater not reaching expected performance or not being driven correctly).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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Repair manuals
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