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Catalyst Monitor not ready but no trouble codes

2001 Prizm/Corolla - CEL is off, no trouble codes, all other monitors are ready, but not the catalytic convertor. No repairs since a new battery mid December. The smog guy (California) says that he can let another monitor go but not the cat; it costs him too many points.

Is this a converter in the early stages of failure (150,000 miles; some oil consumption)? Or is there another possibility?

Have you performed the drive cycle for the catalyst monitor?

If not, here’s the drive cycle.

  1. The Check Engine light must be off.

  2. Get the engine up full to operating temperature and shut the engine off.

3.Turn off all accessories in the vehicle.

  1. Start the engine and bring the idle speed to 1,000 RPM’s for 6-8 minutes.

  2. allow the engine to idle normally for 2 minutes.

  3. Drive the vehicle at a steady speed of 55 MPH for 10 minutes.

  4. Stop the vehicle and allow the engine to idle in drive A/T with the brake pedal applied, in neutral M/T with clutch and brake pedals applied for 2 minutes.

If the readiness monitor does not complete, repeat the above steps.


Tester: That is an interesting cycle. I assume there must be some margin, as I don’t know how you can start up and drive at a steady speed of 55 MPH for 10 minutes without getting a lot of traffic tickets. Perhaps if you pulled off on an expressway, then started the whole sequence?

In fact it is impossible to get to 55 MPH without spending at least a few seconds at a slower speed.


There are different drive patterns that what was posted above for this car, search out Toyota TSB EG003-02. It has all the correct drive cycles listed and conditions that must be met for your monitors to set.

Steve Here is the link.

@64Impala Unless I’m extremely mistaken, you’re allowed to have 1 incomplete monitor, even if it is cat

Offhand, it sounds like the guy doesn’t want to smog your vehicle, but I think he would be legally allowed to smog it

If I were you, I’d call or visit another smog station, and ask the guy if he’s willing to smog it, if all monitors are complete, except cat

Got nothing to lose except a phone call, or a quick trip to another smog station

Thanks to all who responded!

I should have specified that I completed the Toyota-specified drive cycle for the catalytic converter monitor. Also to be precise, the O2 sensor and heater monitors are set, and there are no pending codes either. (Thanks to Steve for posting the link to the Toyota monitor drive patterns; it takes a bit of work to find - that is indeed the guide I used.)

To summarize: 2 months of mixed street/freeway driving and execution of the specified drive pattern, all other monitors set, but not the cat monitor, and no trouble codes current or pending. Ideas, please?

You are allowed 1 monitor to be unset. The shop is worried about keeping their star rating. I would look for a shop using the new ois system. It is much quicker and your car should pass using it.The way the state has the star system setup cars that should pass are failed so the shops star score is not affected, it’s a flawed system.

Yes, the operator said didn’t want to lose points, but he also said that no one would run it with the cat monitor not ready, implying that the state was running some kind of crackdown.

What is the ois system?

@64Impala please just call or visit another smog station, and explain the situation

I still think one of them will smog your car

Don’t take the guy’s word for it. Find out for yourself

The DAD ois is the new system for cars 2000 and newer it plugs directly into the obd port and looks at the vehicles computer data. The car is not drive on a dyno and the tech does not see which monitors have run or not. Call your local dealer and ask if they are using the new system, most are as it is quicker and less costly to maintain.

My car is 2005, and it got “smogged” a few months ago. I put smogged in parentheses because it’s exactly as @SteveC76 described. The guy hooked up to the 16 pin dlc, and I was out of there in less than 5 minutes

It was a STAR station, if that matters . . .

The DAD ois is the new system for cars 2000 and newer it plugs directly into the obd port and looks at the vehicles computer data

What about 1996-2000? We have never run OBD-II compliant cars on dyno for emissions, that’s the whole point of OBD-II.

I’m in Washington State, what are these points people are referring to? What’s the difference to the shop if the car passes or fails? Seems like that’s the customer’s problem.

The monitor standards are changing with the switch from the tailpipe monitor system (BAR-97) to the OBD Inspection System (OIS):

Gasoline-powered vehicles model-years 1996 through 1999 with more than one (1) incomplete monitor;

Gasoline-powered vehicles model-years 2000 and newer with any incomplete monitors, excluding the evaporative system monitor;

So the smog check guy is probably using the OIS system, which is mandated for all beginning March 9 2015.

So I am back to my original question: what is going on to keep the cat monitor from setting?

The rear O2 may be lazy. I would replace it. Someone with a good scanner could see it slow switching, but that would cost at least a $100 diag fee.

@knfenimore The rear O2 sensor isn’t supposed to be switching rapidly

If it is, that doesn’t bode well for the cat

You may have to experiment a bit to get it to set. Do you own an OBD II tool? They aren’t super expensive and are reported to be easy to use. You may just have to repeat that protocol a few times, and keep checking on your own.

I think if I had this problem I’d visit a Toyota dealership shop and ask them what driving pattern is needed for that monitor to complete. They probably deal with this quit a bit, and they are the experts. Visit during a day/time when they aren’t very busy.

It’s also possible the ECM is losing power for some reason, temporarily. That could cause this symptom. The ECM would randomly keep starting over with the monitors. And maybe the cat monitor is just the one that takes the longest to complete. A bad/loose fuse to the ECM, bad battery connections, battery on the fritz that drops out on bumps, etc. Maybe get your charging system and battery tested.

All this sound pretty frustrating. All you want to do is get the car smogged, but no clear way to get past this hurdle. If all else fails, you might try phoning up the Calif BAR and see if they can offer a solution. Or take another look at their website. Unfortunately, if the website is still like it was when I was going through a similar problem about a year ago, the BAR website isn’t very well organized, almost to the point where it appears the BAR is trying to obfuscate the issues and how the owner can resolve them for some reason. But if you phone you may get someone willing to help. If this is the first time this has happened, I think there’s probably a second way to get around all this. But you’d have to fix it by the time the smog test is needed again, in two years.

At this point I would try doing a code clear and disconnecting the battery. Then perform the drive pattern again. When I do the drive patterns I usually go out on the freeway in the early morning and follow the pattern as closely as possible.

Steve, have you had any experience that disconnecting the battery would fix a monitor not ready problem? I replaced the battery not too long ago (mid December), so the car has had that experience.

Asemaster, I’m dealing with California standards.

I’m going to try Cataclean first to see if I can avoid more expensive repairs involving tight spots and bruised knuckles - I’ll report back.

I have done it in the past when fighting with a difficult to set monitor. I perform a code clear at the same time even if there are not any codes. It’s like resetting your pc when a program hangs.