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P0133 Code: Meaning, Symptoms, Causes, Diagnostics, And Fixes

The P0133 OBD2 code activates when the upstream oxygen sensor isn’t responding as quickly as it should. While this is a relatively minor issue on its own, it can make it more difficult for your engine to maintain the right air-to-fuel ratio.

P0133 is a relatively minor trouble code, but it’s still enough to make you fail your next emissions test. Your vehicle will also release more harmful emissions while this trouble code is active. Because of this, it’s a good idea to find and fix the problem as soon as you can.

In many cases, this is a very affordable trouble code to fix. You may simply need to clean one of your sensors or replace a damaged wire. In any case, the steps below will help you to pinpoint the issue. 

P0133 Code Definition

  • P0133 Generic: Oxygen Sensor Circuit Slow Response (Bank 1, Sensor 1)
  • P0133 Ford: O2 Circuit Slow Response (Bank 1, Sensor 1)
  • P0133 Hyundai: (O2) Circuit Slow Response (Bank 1, Sensor 1)
  • P0133 Jeep: O2 Sensor 1/1 Slow Response
  • P0133 Toyota: Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1)

What Does P0133 Mean?

The oxygen sensors in your exhaust system send information to the engine control module (ECM) or powertrain control module (PCM) about the air-to-fuel ratio. This is conveyed as a voltage measurement. When it drops too low, the mixture is too lean. A high voltage indicates a rich air/fuel mix.

In response to this data, the ECM or PCM adjusts the mix accordingly. These small adjustments limit the smog-forming compounds in your exhaust and maximize your gas mileage. 

There are two oxygen sensors in your exhaust system. The P0133 code refers specifically to oxygen sensor 1, also called the upstream oxygen sensor. It measures the air going into the catalytic converter. This data is then compared with oxygen sensor 2, or the downstream oxygen sensor, to ensure the exhaust system is functioning correctly.

The voltage reading of the upstream oxygen sensor should go up when you press on the gas. If it responds too slowly, the P0133 OBD2 code will trigger. 

While P0133 is a generic powertrain code, the specific repair steps can vary depending on your vehicle. You may find technical service bulletins related to this code for your make and model. It’s also a good idea to check your vehicle’s manual for repair suggestions before starting the generic diagnosis below.

What Are The Symptoms Of The P0133 Code?

In some cases, you won’t notice any drivability issues. If there are symptoms, they include:

  • Activation of the check engine light
  • Reduced fuel economy
  • Reduced engine power
  • Rough engine running
  • Rough idles and stalling
  • Smoke in the exhaust

What Are The Causes Of P0133?

  • Faulty oxygen sensor
  • Carbon build-up in oxygen sensor ports
  • Damaged or faulty wiring around the oxygen sensor
  • Vacuum or exhaust leaks
  • Fuel pressure too low
  • Mass Air Flow (MAF) Sensor is dirty

How Serious Is The P0133 Code?

The P0133 is a low severe diagnostic trouble code (DTC). If you do have symptoms, they’re likely to be mild, and the risk of engine damage is low. Having said that, your car may emit more pollutants while this code is active. You should address it as soon as possible, and will at least need to repair it before your next emissions test. 

How To Diagnose And Fix The P0133 Code

Tools you’ll need:

We use an OBD2 scanner to diagnose the P0133 code.
We use an OBD2 scanner to diagnose the P0133 code.

How To Diagnose And Fix The P0133 Code

  1. Use the OBD2 scan tool to check for other trouble codes and read the freeze frame data. Verify the conditions under which the code initially set, then clear the codes and test drive your vehicle.
  2. If the code comes back, start by inspecting the wires around the oxygen sensor. Replace any that are damaged or frayed.
  3. Check the oxygen sensor for dirt and corrosion. If you find any, remove the oxygen sensor and clean it using MAF sensor cleaner. Ensure all wires are firmly connected when you reinstall it.
  4. Check for vacuum leaks in the exhaust system. Pay close attention to the ends of hoses, where fraying is likely, and ensure they’re all firmly connected. 
  5. Inspect the MAF sensor for dirt or corrosion. False readings from the MAF sensor can affect the response of the oxygen sensor. Clean it with MAF sensor cleaner, then clear the codes to see if P0133 returns.
  6. Use a digital multimeter to test the voltage of the oxygen sensor. Warm up your vehicle, then connect the positive lead of the multimeter to the sensor’s connector. Attach the black lead to the negative battery terminal or a ground point on the chassis. Ensure the car is in park with the emergency brake on, then have an assistant rev the engine. The sensor’s voltage should rise as you add fuel. If it doesn’t change, there is likely an issue with the sensor or the wiring.
  7. Test the wiring around the oxygen sensor for open circuits and shorts, even if there is no visible damage. Replace any faulty wires found in your diagnosis. If no faulty wires were found, or if the code still will not clear, replace the oxygen sensor. 

Common Mistakes To Avoid While Diagnosing The P0133 Code

While a faulty oxygen sensor is often the cause of the P0133 trouble code, this is not always the case. Make sure you check for vacuum leaks and damaged wires before replacing any components. If a sensor does seem to be failing, try cleaning it before you replace it. 

Tips To Avoid P0133 In The Future

Build-up on the sensors can impede their readings and cause trouble codes such as P0133 to trigger. Leaks in other engine systems are a common cause. Exhaust leaks can cause soot to accumulate on the oxygen sensor base. Dripping fluids can also dirty the sensor, even causing failure.

Proper preventative maintenance is the best way to prevent this. If you notice any fluids dripping from your engine, locate and repair the source, even if no trouble codes have triggered. 

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