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Troubleshooting Catalyst Monitor Not Ready Issue In 7 Simple Steps

The OBDII (On Board Diagnostic) System regulates the vehicle’s performance with the help of monitors. Two types of monitors are present in our vehicles – continuous and non- continuous. Continuous monitors operate as long as the engine runs.

Whereas, non-continuous monitors need certain conditions like speed, ambient, acceleration, fuel level, and much more to carry its testing process. Catalyst Monitors are non-continuous monitors that assess the ability of the catalytic converter to decrease harmful emissions.

But, what if your vehicle indicates ‘catalyst monitor not ready’? So, let’s explore further how to make your vehicle’s catalyst monitor ready!

7 Steps to Follow When Catalyst Monitor Not Ready

The output of the catalyst monitor can be either ‘not ready’ or ‘ready.’ If the output of the monitor is not ready, what does that indicates? It signifies that the requisite Drive Cycle has not run completely; thus, the catalyst monitor has not tested the catalytic converter.

So, in order to make the status of catalyst monitor ‘ready’, you need to follow these simple steps.

1. Make Sure the Engine Light is Off

The first and foremost step is to check whether the engine light is off. If your vehicle has active trouble codes, it may stop a monitor from running completely.

2. Check if your Vehicle has a Coolant Temperature

The drive cycle starts with a cold start. The engine coolant temperature of your vehicle should be below 50°C (122°F) and within 6°C (11°F) of the air temperature. You can achieve this by allowing your car to sit overnight.

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3. Let the Engine be Idle for 2 Minutes

Issues of catalyst monitor not ready

The next step is to start the engine and keep it idle for two and half minutes, keeping rear defroster and AC on.

4. Drive the vehicle at a Steady Speed of 55 MPH

Now, switch the rear defroster and ac off and keep the speed of your vehicle at 90 km/hr (55MPH) nearly for 3 minutes. During this period, the purge and Fuel monitor diagnostics will take place.

5. Decelerate your Vehicle’s Speed at 20 MPH

Make the speed of your vehicle fall gradually up to 32 km/hr (20 MPH). Avoid touching/shifting of clutch or brake.

6. Again Speed Up

Drive your vehicle back to 55MPH (90 km/hr) at 3/4 throttle for nearly five minutes. The catalyst monitor diagnostics will take place during this period. If the battery is detached or the catalyst is not ready, it might take five complete driving cycles to decide the status of the catalyst. For additional information about catalyst monitor, one can refer to maintenance tips by car experts.

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7. Stop the Vehicle

Now, make your vehicle slow down and allow it to sit idle for 2 minutes.

Reasons for catalyst monitor not ready
Steps for catalyst monitor not ready

That’s all. By practicing the above-mentioned steps carefully, you can easily troubleshoot the problem of ‘catalyst monitor not ready.’ Next time your vehicle shows such kind of signals; don’t forget to follow these steps.

13 Comments
  1. Anthony Kwan says

    I followed your instructions exactly this morning and it fixed the monitor not ready issues. My Miata passed the smog check without any problem. Prior to that I had wasted so much time driving , putting hundreds of miles without any results. Thank you very much for being so helpful. I will recommend this procedure to any one who needs it.

  2. Douglas says

    Brilliant! I wasted two weeks trying to figure out how I’m going to pass emissions and even after bringing it to two shops they couldn’t help me. I found this thread and tried it out on my 2004 ford van and it passed right after. Thanks!

  3. John says

    Wow, this actually did work like a champ… my mother had a new battery installed in her 98 Mazda which wipes everything clean and right before scheduled emissions test. She barely drives it and kept showing 4 modules not active… drive 50 miles and stilled showed 2 not active, one of which was the catalyst (mandatory for that one)… followed directions x 4 and passed 2 days later. Be aware it’s not safe or wise to attempt this on interstate and slow down to 20 mph, but do best you can in a safe manner and your good!

  4. Julia says

    I would love to try to to fix my catalyst problem. However, I live back country roads with stop signs and short roads. It is about 2 miles to the main road. How can I run this test properly when I have to stop and start twice before highway? Thank you

    1. Bill says

      Go out very early on a Sunday morning and do the same. You don’t have a stop sign, imagine one. Leave a mile or so between stops. You can also do the 55 MPH test the same way without getting in anyone’s way.

  5. TopSpeed says

    After going through 3 smog shops and my own indi, they couldnt figure it out. Did it one time and it worked. Thank you!

    2000 BMW 323i

  6. Eduardo says

    Im still having problems I do every step and still doesn’t work I been trying to fix this problem but smog check still won’t pass catalyst not ready set all monitors. I have a Nissan Altima 2009 I took my car to the dealer and the only thing they said is not ready drive more miles. I drove 600 miles already I tried everything but still doesn’t work. I been doing this for a month already.

  7. John says

    Works. I drove 400 miles then tried this what worked for me is driving 20 min at 55 per hour exactly 55 and not using autopilot

  8. Bong says

    Worked like a charm. For safety concerns I did the drive late at night on the freeway when traffic is light. At the point where I slowed 20mph, I turned on my hazard lights.

    1. Bong says

      Forgot to mention this was for a 2003 Toyota Tacoma 4WD

  9. Rod says

    Drove 1500 miles but catalyst was still showing not ready. Did this procedure once and it cleared the catalyst. Big help, big sigh of relief. Thanks a lot.

  10. Liz says

    You are really awesome! Thank you very much for your posting. I tried your advise and it worked. I tried it just one time and by following each steps of your instructions. But, I turned on my hazard light while driving the 20 MPH. And so then i brought the car back to the garage, i was told catalyst was “cured” and my car 2006 Acura RSX passed the emission test! And to think that I have spent 2 days and going back and forth from several garages say around 6 times and each time I was advised to drive some more and some more to build the mileage. That didn’t work for me but your technique works! Thank you!!!

  11. Julie says

    I’ve had my Hyundai Sonata (2005) for 14 yrs. This year (2021) will be my 5th time doing a drive cycle. well, I actually don’t do it. I’ve had others do it for me (2x on a Dyno & 2x on the road). My car’s drive cycle is not what is described by the author here (unfortunately). It is much more complicated and hard! Requires idle for 5 min, driving at 50 for 8 min, idle for 15 min, driving for a minute at 55 & idling for a minute (both twice). Then doing a bunch of driving at 40 mph & 50 mph (6x) for a minute at 40 & 5 seconds at 50. It is nearly impossible for the average person to do this. The Dyno is the way to go! When it was driven on the road, I don’t know where they drove it. It was outside the city & 75 miles from where I live.
    Anyway, this ends up costing me $150 each time. I will be paying it again, & I am not happy. I’m mad at the State of California & their silly requirement that all monitors be ready. The Referee is no help either because they should take care of this & they have the ability to do so. I also want to point out that my car has had bad batteries installed that last only a year (2x, I think) (Thx AAA). So, after the car passes it’s smog w/ monitors ready, six months later the battery dies. One time I had the vehicle serviced for a new timing belt and the shop messed it up & cleared the monitors so at my next smog, monitors were not ready again. The State of California should be aware of stuff like this, and make some cars EXEMPT to a smog–especially if it’s only a single monitor not being ready–and nearly impossible to get ready.

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