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How many miles do I need to drive to get the Catalyst monitor ready for smog test?

My car<1997, Toyota, Corolla> failed smog test a month ago and an auto repair shop did fixing and cost me $550. And I went to the smog test only center again, but I was told to drive 100 miles to get car ready for the test. After driving 200 miles, today I went back to the smog test only center, but I was told to drive 100 miles more because the Catalyst monitor is still not ready.

I need to know how many miles do I need to drive to get the Catalyst monitor ready for smog test.

Thanks very much for your time and attention!!

I looked up what it takes to reset readiness monitors for the catalyst system and it doesn’t take much. Only normal driving. However, it also states that the engine should be allowed to idle until it reaches operating temprature before taking it out for the drive cycle.

So, start the engine, let it idle for 20 minutes, then take it for a drive.


Thank you very much for your reply, Tester.

One more question: what is a drive cycle? And how many drive cycles do I need?

Thanks again!!

Thank you very much for your reply, Tester.

One more question: what is a drive cycle? And how many drive cycles do I need?

Thanks again!!

A drive cycle is where the vehicle is operated under certain conditions where the engine management system is able to relearn the operting parameters.

On some vehicles the drive cycle is very easy. And on others, the drive cycle is very complicated


Thank you very much again for your reply, Tester!

Could you please help find what is a drive cycle for my car: 1997 Toyota Corolla?

Thanks again!!

Start the engine. let it idle for 20 minutes. then drive the vehicle. How simple is that?



Got you. Thanks a bunch for your help!!

Is the check engine light on? What did they do for $550? How many miles on the car?


  1. The check engine light is not on < it was on before fix>
    2.they replaced <1> EGR vacuum modulator valve, <2> O2 sensor, and <3> catalyst converter
  2. There are 164,382 miles on the car

Thanks very much!!

Here’s my advice:
Drive the car on the freeway for at least 1/2 hour at steady speeds before going to the smog station again.

I would also write a letter to your state representative and Senator asking them to take a look at how your states emissions testing program is administered and operated…Today, all that is really needed is a quick inspection of the CEL function…If the light is working properly, the car passes the “test”…There is NOTHING to be gained by subjecting motorists to anything more involved or complex than than that. The FACT is, not enough cars fail these “tests” to make any difference in air quality…It’s just a Dog & Pony Show and a jobs program…

Where I’m at, all monitors must be set.
Well, you’re allowed one incomplete.
And then it still gets the tailpipe test on the dyno.
AND the inspection of the MIL function.

Setting the monitors can take time if you don’t have the procedures to do it. I had the same issue when my battery went dead and had an IM test due at the time. I am glad to say that we finally did away with the required IM testing here. There isn’t many bad smoggers running on the road anymore.

To give you an idea for what typical drive cycles are like, here’s the definition of the General Motors OBDII "drive cycle. It’s from the site. I suspect the “drive cycle” for your Toyota is not identical, but it would need to accomplish similar testing.

To perform an OBDII Driving cycle do the following:
<b>Cold Start</b>. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge “No Flow”, Misfire and if closed loop is achieved, Fuel Trim.

<b>Accelerate</b>. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

<b>Hold Steady Speed</b>. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

<b>Decelerate</b>. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

<b>Accelerate</b>. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

<b>Hold Steady Speed</b>. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

<b>Decelerate</b>. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

In the way of background info, your car computer (the ECM) constantly checks the operation of the cat converter while the car is being driven. It has sensors before and after the Cat, and if the cat is working, the sensor readings confirm this to the ECM. And if the Cat isn’t working, the sensors say this to the ECM too, and if they keep saying the Cat isn’t working, the ECM will turn on the check engine light.

When your new cat was installed, the Cat shop probably reset the ECM. Or they disconnected the battery, which does the same thing. After being reset, the ECM has to read those Cat sensors over the course of several trips, and during different operating conditions. Low speed, freeway speed, low coolant temps, high coolant temps. It’s not simply driving a certain number of miles, the car has to go through all these various prescribed driving conditions before it will finish the ECM reset procedure. So if your 100 miles of driving were all more or less the same type of driving conditions, then it might not reset. It’s a shame the shop isn’t able to tell you what exactly you need to do to finish the reset procedure. There ought to be a regulation for the auto makers about this in my opinion, that the ECM can’t keep secrets from the driver. And I think the smog shop should offer you better guidance too, rather than simply telling you to drive more and come back later.

You might wonder how the Smog shop even knows about all this? When you go to the smog place the first thing they do is hook up their computer to your car’s ECM and see what the ECM has to say. If the ECM says it has recently been reset, your ECM tells this to the smog shop computer. Your ECM in other words tattles on you. This is to prevent the circumvention of the state’s smog laws by simply disconnecting the battery before going for the test.

Thanks for all of you.

Here’s I am gonna do:

Driving cycle <1>: First I will idle 20 minutes, then drive at steady speed on freeway for 1/2 hour

Driving cycle <2>perform an OBDII Driving cycle: Cold Start, Idle, Accelerate, Hold Steady Speed,Decelerate, Accelerate,Hold Steady Speed,Decelerate.

I have somewhere on my HD the drive cycle for readying monitors on Toyota, and it is not simple, period. It involves more than one heat up, one cool-down, and varying speeds of driving in certain sequences and for certain lengths of time. When someone makes an apparently sarcastic comment about how simple it is, they are showing they do not know the Toyota drive cycle.

I just read a forum on Porsche, and one poor guy drove his car many hundreds of miles without ready being set. As I remember, they solved it by having him warm the car up before driving, he had been starting and driving right to the freeway, though I don’t think Toyota is that simple.


So do you know what Toyota drive cycle is?

The catalyst drive cycle from a Toyota bulletin;

The monitor will not run unless:
ECT (Coolant Temp) is 176F (80C) or greater.
IAT (Intake Air) is 14F (–10C) or greater.*

  • For 2002 MY and later vehicles: The readiness test can be completed in cold ambient conditions
    (less than 14F / –10C), if the drive pattern is repeated a second time after cycling the ignition OFF.

Drive Pattern Procedure
Connect the OBDII Scantool to DLC3 to check monitor status and preconditions.
Note the IAT (Intake Air) value during engine startup. The driving time must be adjusted
during step “a” based upon IAT (Intake Air) value at startup.
a. Drive the vehicle at 40 – 55 mph (64 – 88 km/h) for the time described below:
If IAT (Intake Air) was less than 50F (10C) when the engine was started,
drive for 7 minutes.
If IAT (Intake Air) was greater than 50F (10C) when the engine was started,
drive for 3 minutes.
b. Drive the vehicle at 35 – 45 mph (56 – 72 km/h) for approximately 7 minutes.

Drive with smooth throttle operation.
Avoid sudden acceleration.
Avoid sudden deceleration as much as possible with the throttle fully closed.
If readiness status does not switch to “complete,” ensure preconditions are met, turn the
ignition OFF, then repeat steps “a” and “b.”

Note that the engine temperature must be above 176F. Your thermostat opens in the 176-183F range. If you have an old thermostat that doesn’t close tight you may not reach the minimum tempurature for this monitor to start.