Oxygen Sensor Not Ready: Meaning, Causes, and Fixes

Oxygen sensor not ready” is one of the easy-to-fix problems car owners encounter. The fact that it is easy to fix should not deter you from attending to the issue as quickly as you can. This article will highlight the underlying issues that could trigger the “oxygen sensor not ready.” It will also discuss fixing the problem without spending your hard-earned money. 

Oxygen Sensor Monitor Incomplete

An oxygen sensor monitor incomplete means your vehicle’s computer cannot determine if everything in the emission control system is functioning well. So, the OBD inspection will be incomplete. If you have a defective unit or the heater circuit is not good enough, it may keep you from getting your monitor ready. 

The oxygen sensor monitor is a self-check feature that determines the oxygen sensor condition. What triggers the MIL on your dashboard is if the oxygen sensor monitor finds any problem with the oxygen sensor or other components by it. Under this condition, your car will likely fail an emission inspection. Besides, the MIL will not go off until the emission inspection is complete. 

Causes of “Not Ready” Oxygen Sensor Monitor in a Vehicle

Here are a few reasons your Chrysler, Ford, or GM’s O2 sensor monitor will indicate not ready:

  1. An “oxygen sensor not ready” can result from your vehicle’s computer memory reset, which might have happened during an update or a recent repair.
  2. Since the oxygen sensor is in the exhaust stream, it can also become contaminated. Extreme rich fuel mixture conditions or issues with emissions control systems can result in this contamination. The sensor may need a replacement. 
  3. A recently disconnected battery or a weak battery is also a likely cause of this in your vehicle. 
  4. Faulty or damaged alternator.
  5. Incomplete drive cycle.
  6. Another major cause of “not ready” is an oil blow-by in an older engine and engine coolant that is burnt in the combustion chamber. This is often a result of an engine gasket leak.

How to Fix “Oxygen Sensor Not Ready”

  • Ensure your engine is not on. Do not turn the ignition on for at least eight hours before the diagnostic test. The coolant temperature and the air temperature should be 50 C/122 F or less and 11 degrees, respectively.
  • Ensure your car has enough fuel before starting the test. 35% to 85% fuel level is OK.
  • Ensure you clear all DTC or pending ones. If you don’t, the Malfunction Indicator Light will remain on. Having the MIL on may hinder the complete running of a car’s monitor.
  • Start the engine, and turn on the defroster and the air conditioner. Leave the engine idle for 2½ minutes.
  • Once the above time elapses, turn off the defroster and the AC.
  • For three minutes, speed up constantly between 55 to 60 mph. Then steadily decelerate to 20 mph without using your brake.  
  • Repeat the process three more times.
  • Drive between 50-100 miles at highway speed. During this process, the monitor diagnostics will occur.
  • Complete the OBD II drive cycle to bring the monitor to a complete status. Completing your drive cycle enables the monitors to determine any potential issues connected to the emission system. Driving your car at a given speed for a specific length of time will help get the monitor ready. 

Chrysler vs GM: How to Complete Drive Cycle for O2 Sensor Monitor 


  • Sep 1: Start your car engine 
  • Step 2: Idle for about 5-7 minutes
  • Step 3: Allow the system to hit closed loop operation
  • Step 4: Steadily drive your Chrysler for 2 minutes above 25 mph speed. 
  • Step 5: Brake and stop for about two and a half minutes 
  • Step 6: Smoothly accelerate to 35-45 mph 
  • Step 7: Repeat steps 5 &6 multiple times

GM: Typically, General Motors models, like Chevrolet, use a two-part O2 sensor monitor. 

  • Start the engine 
  • Switch on the AC and defroster
  • Let it idle for about 3 minutes
  • The first part of the two-part O2 sensor monitor will run first
  • As it’s running, it checks the sensor heater circuit.
  • Switch off the AC and defroster
  • Press the gas pedal and accelerate to 55 mph while at half throttle 
  • Hold the throttle at a steady speed of 55 mph for about 2 and a half minutes.
  • The second part of the two-part O2 sensor monitor will run.  


How can I keep my oxygen sensor ready?

First, reset the car’s computer. Then drive your car, covering a distance of 50 to 100 miles. Your monitor needs driving to check the sensors and determine any potential problems.

Will my engine operate in the absence of oxygen sensors?

Your Power Control Module will be unable to determine the fuel to supply the engine if your 02 sensors are not working. But, of course, your engine will operate. 

How will I figure out if my drive cycle is complete?

Do not start the engine for at least eight hours. Drive at a steady highway speed for 15 minutes. For twenty minutes, drive with 30 seconds of idle time in between.

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Final Thoughts 

“Oxygen sensor not ready” should not be a cause for panic. It is a clear indication that your Onboard Diagnostic System (OBDII) cannot carry out a check on the emission control system. So, the steps above can assist you in fixing the problem as a DIYer. If those steps do not rectify the problem, your car may need repair. You will need to seek the expertise of a technician to help you inspect your car and diagnose the trouble. 

Overall, “oxygen sensor monitors incomplete” do not always require elaborate or costly repairs. Just driving your car around at a specific speed limit for a specific period may be all that your car needs.   

  • James Smith

    I'm James Smith, a car enthusiast and a content writer for Daily Car Tips. I have a passion for all things cars, from classic muscle cars to the latest electric vehicles. When I'm not writing about cars, you can usually find me tinkering with my car or checking out the latest automotive trends.

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