🚨 Diagnostic Profile
- Vehicle/Equipment Make: CADILLAC
- Technical Description: HO2S Bank 2 Sensor 3 Rich Or High Voltage
This code is a Powertrain (P) code monitored by the Engine Control Module (ECM) or Powertrain Control Module (PCM). It indicates that the Heated Oxygen Sensor (HO2S) located on Bank 2, Sensor 3 (typically a secondary sensor positioned after the catalytic converter on vehicles with multiple catalyst monitoring points, or a third sensor in a dual-catalyst bank configuration) is reporting a voltage signal that is consistently higher than expected, suggesting a rich fuel condition. The PCM interprets this as either an actual rich exhaust condition (too much fuel, not enough oxygen) or a wiring/sensor fault causing a false high-voltage signal. This can stem from fuel delivery issues, a failing sensor, contamination, or wiring faults causing a skewed voltage reading. A rich condition on Bank 2 specifically points technicians toward that cylinder bank’s fuel trims, injectors, and air/fuel metering components.
🚨 Repair Difficulty Tier
- Difficulty Rating: Intermediate
Diagnosing this code requires a capable OBD-II scan tool that can display live and freeze-frame oxygen sensor voltage data, along with fuel trim values for Bank 2. A digital multimeter is useful for verifying wiring integrity and sensor heater circuit resistance. While sensor replacement itself is a moderate DIY task, pinpointing whether the root cause is the sensor, wiring, or an actual rich fuel condition (such as a leaking injector or failing fuel pressure regulator) requires diagnostic experience and proper data interpretation.
🛠️ Resolution Steps
- Step 1: Preliminary Inspection
Begin by visually inspecting the wiring harness and connector for HO2S Bank 2 Sensor 3, checking for corrosion, chafing, or damaged insulation near the exhaust system where heat exposure is common. Inspect the sensor itself for physical damage, oil fouling, or carbon buildup, which can indicate a rich-running condition. Check for exhaust leaks upstream of the sensor that could skew readings. - Step 2: Diagnostic Verification
Connect a scan tool and monitor live data for HO2S Bank 2 Sensor 3 voltage, along with Short Term and Long Term Fuel Trims (STFT/LTFT) for Bank 2. A voltage reading pegged high (above 0.8–1.0V) with corresponding negative fuel trims confirms a rich condition. Use a digital multimeter to verify sensor signal and heater circuit voltages against factory specifications, and perform a wiggle test on the harness to rule out intermittent wiring faults. - Step 3: Resolution & Reset Process
If the sensor itself is confirmed faulty (slow response, stuck voltage, or heater circuit failure), replace the HO2S Bank 2 Sensor 3 with an OEM-spec unit. If wiring is damaged, repair or replace the affected harness section and ensure proper connector seating. If the fuel trims indicate an actual rich condition, inspect for a leaking fuel injector, faulty fuel pressure regulator, or MAF sensor miscalibration on that bank. After repairs, clear the code using the scan tool and perform a drive cycle to confirm the PCM no longer detects the fault and readiness monitors complete successfully.
📦 Parts, Labor, and Budget Estimates
- Required Components/Software: OEM-spec Oxygen Sensor (HO2S Bank 2 Sensor 3), wiring harness repair kit (if needed), OBD-II scan tool with live data capability, digital multimeter
- Average Component Price: $60 – $150 USD
- Estimated Labor Hours: 0.5 – 1.5 hours (additional time required if fuel system diagnosis is needed)
- Total Estimated Budget: $120 – $300 USD (higher if fuel injector or fuel pressure regulator replacement is required)