Code
P1165
HUMMER
P — Powertrain
Heated Oxygen Sensor (HO2S) Cross Counts Bank 2 Sensor 3
AI status
Completed
Completed
100%
Causes
- Faulty HO2S (Bank 2 Sensor 3)
- Open/shorted or corroded wiring or connector (signal or heater circuit)
- Heater circuit failure (open fuse/relay, poor ground, wiring fault)
- Contaminated or aging oxygen sensor (silicone, oil, antifreeze contamination)
- Exhaust leak upstream of the sensor or at the sensor flange
- Degraded or damaged catalytic converter on Bank 2
Symptoms
- Check Engine Light illuminated (MIL)
- Poor fuel economy or richer/leaner-than-normal running
- Failed emissions readiness or emissions test failure
- Possible rough idle or hesitation if upstream issues present
- Reduced catalyst monitoring or drivability complaints under some conditions
What to check
- Read and record freeze frame and all stored DTCs; note related fuel trim or misfire codes
- Scan live O2 sensor data for Bank 2 Sensor 3 and compare waveform to the corresponding upstream sensor(s)
- Verify heater circuit operation: check for battery voltage on heater feed when commanded and check heater resistance with sensor disconnected
- Inspect wiring harness and connector for corrosion, damage, heat exposure or poor grounding
- Perform visual inspection for exhaust leaks at flanges, gaskets, or pipe joints upstream of the sensor
- Check long- and short-term fuel trims and fuel pressure for conditions that could affect O2 switching
Signal parameters
- Narrowband O2 voltage typically switches roughly between ~0.1 V (lean) and ~0.8–0.9 V (rich); downstream sensors often show steadier voltages near midrange if catalyst is functioning
- Cross-counts: number of rich/lean transitions over a drive period — abnormal counts indicate too few or too many transitions compared to expected
- Heater circuit: commanded to supply battery voltage pulses; heater resistance typically low (varies by sensor design—check OEM spec)
- Response time: properly functioning sensor shows timely transitions after fuel trim changes or load events; slow or no transitions indicate sensor/heater/circuit or exhaust problems
Diagnostic algorithm
- Retrieve and record all DTCs and freeze frame data. Identify related codes (O2 heater, fuel trims, cat efficiency, misfires).
- Clear codes and attempt to reproduce. Monitor Bank 2 Sensor 3 live data during warm-up and steady-state runs; note switching behavior and compare with Bank 2 upstream sensor(s).
- Verify heater circuit: with ignition on (engine off) check for battery voltage at heater feed and a good ground reference; measure heater resistance at sensor and compare to OEM spec.
- Inspect wiring and connector for damage or corrosion; backprobe signal and heater circuits while monitoring for intermittent faults during wiggle test and engine heat cycles.
- Check for exhaust leaks upstream of the sensor (use smoke test or visual inspection). Repair leaks before further testing.
- Evaluate fuel system and engine mechanicals: check long/short-term fuel trims, fuel pressure, vacuum leaks and misfires that can alter O2 behavior.
- Use an oscilloscope to confirm sensor waveform shape, amplitude and switching frequency; verify cross-counts against expected behavior or bank 1 reference.
- If wiring and vehicle systems are good, replace the Bank 2 Sensor 3 with OEM-equivalent sensor. Clear codes and perform drive cycle to confirm code does not return.
- If code persists after replacement, inspect catalytic converter efficiency on Bank 2 (temperature testing across converter, exhaust back-pressure, or lab-grade catalyst tests) and consider ECM/ground diagnosis as last resort.
- After repair, erase codes and complete required readiness/drive cycle before returning vehicle to customer.
Likely causes
- Failed or slow HO2S (sensor not switching as expected)
- Wiring/connector fault to Bank 2 Sensor 3 (intermittent/open/short)
- Heater circuit not operating (sensor cold, poor response)
- Exhaust leak or upstream issue altering sensor readings
- Catalyst degradation downstream
Fault status
Status
HO2S Cross Counts Abnormal — Bank 2 Sensor 3: oxygen sensor switching behavior out of expected range (heater/sensor/circuit/exhaust/catalyst issue suspected).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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