View source for 16517/P0133/000307

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== P0133 - Oxygen (Lambda) Sensor B1 S1 ==
=== P0133 - Oxygen (Lambda) Sensor B1 S1: Response too Slow ===

=== 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: [https://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info 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 [https://wiki.ross-tech.com/wiki/index.php/Official_Factory_Repair_Information 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 [https://wiki.ross-tech.com/wiki/index.php/Official_Factory_Repair_Information 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.