Oxygen sensors detect the oxygen content in the exhaust gases leaving the engine. They constantly transmit this information to the powertrain control module (PCM) in the form of a voltage reading. The engine computer uses this information, together with data relayed by other sensors, to regulate the amount of fuel injected into the engine.
When there is a delay in the voltage switch of the bank 2 downstream oxygen sensor, onboard diagnostics may log the P0133 code.
What Does the P0133 Code Mean?
Diagnostic Trouble Code (DTC) P0133 stands for “Oxygen Sensor Circuit Slow Response (Bank 1, Sensor 2).” It is triggered when the downstream oxygen sensor (located after the catalytic converter) in Bank 1 takes too long to transmit signals to the PCM.
Although the downstream oxygen sensor’s signal does not switch back and forth rapidly like the upstream does, it does change to some degree. A problem arises whenever the PCM does not receive signals from the bank 1 sensor 2 oxygen sensor quickly or frequently enough for the vehicle to run efficiently.
That being said, on most vehicles, if the upstream (primary) O2 sensor signal becomes unreliable to the point that the ECM/PCM knows it can no longer trust that signal, the downstream O2 sensor that usually monitors oxygen storage capacity in the catalytic converter will become the ECM/PCM’s primary input for fuel trim adjustments.
On most vehicles, if the upstream (primary) O2 sensor signal becomes unreliable to the point that the ECM/PCM knows it can no longer trust that signal, the downstream O2 sensor that usually monitors oxygen storage capacity in the catalytic converter will become the ECM/PCM’s primary input for fuel trim adjustments.
– Richard McCuistian, ASE Certified Master Automobile Technician
P0133 on Some Ford Vehicles
Code P0133 may appear on some Ford vehicles. On a 1999 Ford F-150 4.2L V6, for example, this DTC is caused by the following conditions:
- Contaminated HO2S sensor
- Exhaust leaks
- Shorted /open wiring
- Improper fueling
- MAF sensor
- Deteriorating HO2S sensor
- Inlet air leaks
It should be noted that the HEGO Monitor (Heated Exhaust Gas Oxygen sensor) checks the heated oxygen (HO2S) Sensor frequency and amplitude. If during testing the frequency and amplitude were to fall below a calibrated limit, the test will fail.
What are the Possible Causes of the P0133 Code?
- Faulty oxygen sensor/air-fuel ratio sensor
- Malfunctioning oxygen sensor/air-fuel ratio sensor heater circuit
- Circuit issues, such as damaged wiring or poor connections
- Exhaust system leak
- Malfunctioning PCM (in some cases, a software upgrade may be needed)
What are the Common Symptoms of the P0133 Code?
Check engine light is Illuminated
In some cases, the only symptom that vehicle owners experience is an illuminated check engine light. The vehicle must be connected to an OBD scan tool to retrieve the trouble code to confirm that the warning light was triggered by an O2 sensor slow response error code.
Engine performance problems
The P0133 code is sometimes accompanied by symptoms linked to poor engine performance but won’t typically cause poor engine performance.
How to Diagnose the P0133 Code
Evaluating oxygen sensor performance will require some technical diagnostics knowledge. If you’re not keen on troubleshooting your own vehicle, it’s a good idea to seek the help of a licensed mechanic.
If you are an experienced DIYer with advanced automotive know-how, you may check out this video to get an idea of what the diagnostic process might involve:
How to Fix the P0133 Code
If you have DIY car troubleshooting experience, you may try using a scan tool utility to diagnose P0133.
Note, however, that vehicles of different makes and models may experience common symptoms associated with the P0133 code. Repair information for this code may be vehicle-specific. For instance, the steps for fixing a P0133 code in Ford vehicles may differ from the steps for resolving the code in Suzuki cars.
Bring your vehicle to the nearest auto repair shop to get expert advice on diagnosis and repair from a mechanic. If you plan on fixing this code on your own, you may refer to repair manuals or an ALLDATA vehicle subscription for factory repair information.
Products Mentioned in this Guide
Oxygen Sensor
Catalytic Converter
Technical Reviewer at CarParts.com
Automotive and Tech Writers
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