16517/P0133/000307

Possible Symptoms

• MIL (Malfunction Indicator Lamp) ON
• Poor fuel economy
• Increased emissions or failed inspection
• DTC stored in ECM

Possible Causes

• Aged, contaminated, or faulty Oxygen Sensor 1 Before Catalytic Converter -GX10- (Bank 1 Sensor 1)
• Exhaust leak ahead of the front oxygen sensor
• Wiring or connector faults at the front oxygen sensor or its heater circuit
• Air leaks or unmetered air (intake vacuum leaks, PCV issues)
• Fuel delivery or mixture control issues affecting lambda dynamics (fuel pressure, MAF faults)
• Sensor contaminated by silicone, coolant, or leaded additives
• ECM software calibration issues (in rare cases)

Monitoring Conditions

• Monitor Strategy: Front O2 signal dynamic check
• Malfunction Criteria:
  • Delayed response
  • Slow transition
  • Delayed response while avoiding controller oscillations

Possible Solutions

• Address any related DTCs first (misfire, fuel trim, MAF, exhaust leaks)
• Inspect wiring, grounds, and connectors for Oxygen Sensor 1 Before Catalytic Converter
• Verify heater circuit operation for the front oxygen sensor
• Inspect exhaust system for leaks ahead of B1 S1
• Check fuel trims and correct intake leaks or MAF faults
  • See: Fuel Trim Info
• Evaluate sensor switching speed with scan data or scope
  • Induce lean and rich conditions and confirm lean↔rich transition times meet thresholds
    • (verify exact test procedure and thresholds with Official Factory Repair Information)
• Replace the front oxygen sensor if slow response is confirmed
• Perform any required basic settings or adaptation resets after repairs per Official Factory Repair Information

Special Notes

• We always recommend to use original equipment replacement parts, not all sensors are created equally.
• After replacement, clear DTCs and road test to confirm repair.