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luvbeefcakes
12-18-2008, 12:11 AM
I have tried for two months to get my 01 chevy cavalier to pass an emmissions test. Every time it comes back OBD NOT READY. Specifically the Fuel Sys, Comp, and 02 sensor read NOT READY. I have driven the car about 50 miles today and tried the emmissions test twice, both with the same result. Every time I've tried the test it has been burning natural gas. There are no check engine lights on or anything abnormal, and the car runs perfectly fine in both natural gas and regular gas. Any ideas how I can get this car to pass an emissions test. It's obviously a problem with the car's self testing system.

nttrainer
12-18-2008, 12:53 AM
You have to run it through a drive cycle on both fuels.

I have an OBD Scan tool that tells me when the sensors are ready.
Some sensors only reset when driving on gasoline.

For the first drive cycle turn the vehicle off and remove the CNG 20amp fuse in the fuse box under the hood. That insures that the vehicle will run a cycle on gasoline.

Do the following:

1 - Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F and within 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.

2 - 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.

3 - Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

4 - Hold Steady Speed. Hold a steady speed of 55mph for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

5 - Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. Let the vehicle coast along gradually slowing down to 20 mph. During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

6 - Accelerate. Accelerate at 3/4 throttle to 55-60mph. This will perform the same diagnostics as in step 3.

7 - Hold Steady Speed. Hold a steady speed of 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.

8 - Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the brakes or shift gears.


Now turn the vehicle off, put the 20amp CNG fuse back in and repeat the cycle on CNG. Make sure the car is running on CNG !! You don't need to do the Cold Start again (step 1). I usually have my drive arranged so that I drive to the mechanic with the car running and leave it running until he has done the emission test.

I had the "sensors not ready" problem with the first 2001 Cavalier I sold and then I found this procedure and I've used it on every Cavalier I've taken in for emission testing and it's worked every time.

It's important to have the vehicle off when removing and replacing the fuse. You don't want to short anything out.

Hope this helps....

afvman
12-18-2008, 08:22 AM
nttrainer,

Great response! You should put that one in the Library.

B/R,

afvman

freedml
12-18-2008, 08:48 AM
A day or two of 'normal driving' will also accomplish this. I have an OBDII interface for my laptop which also tells me when a car is 'emissions test ready.'

kirkbenge
12-18-2008, 09:21 AM
I had the same problem with my '01 cavalier, Fuel Sys, Comp, and 02 sensor read NOT READY. I didn't go to the same extent that nttrainer went to, but I was told that I needed to have the car run at a steady speed (between 55 and 60 mph) for at least 5 to ten minutes. I told the tech at the I/M shop that I'd be back in twenty, and got right onto a nearby highway and drove at exactly 55 mph for about 10 minutes... When I got back to the I/M shop, all the codes were ready.

nttrainer
12-18-2008, 10:54 AM
A day or two of 'normal driving' will also accomplish this. I have an OBDII interface for my laptop which also tells me when a car is 'emissions test ready.'

It just depends on which sensors are "not ready". You can drive all you want on CNG and some of the sensors (Evap Sys, Catalyst, O2 Sensor) won't go to ready until you drive on gasoline.

The drive cycle is from GM (thanks CNG Utah). It is intended to cover the procedure necessary to reset all sensors.

I'm attaching a failed emission report from Utah that shows which sensors were not reset by only driving on CNG. This test was done after almost 200 miles of "normal driving" but only on CNG. When we followed the drive cycle on gasoline all the sensors went to "Ready" state.

The OBDII code reader that I have will tell me if a vehicle is "emissions test ready" also but it only reports for the fuel that the vehicle is currently running on. I've had it tell me that it's ready when I'm driving on CNG but when I switch over to gasoline it's not ready.

larrycng
12-18-2008, 10:58 AM
You're doing all the right things.

Remember, that with OBDII, one monitor not running to competion will cause another monitor not to run. For example, if the O2 monitor does not complete then the misfire monitor, fuel system (fuel trim) monitor, and CAT monitor will not run because they are dependent on a properly operating O2 monitor to run their tests.

If necessary you can use "Mode 6" to check if some of the components are marginal on their test results. The computer based Autoengineuity scantool has mode 6 capability as do most of the newer factory scantools

After you pull the fuse and reset the monitors for the second test, you should not get the EVAP monitor to run because of the engine temperature conditions. That would be normal on many of the GM products.

Larrycng

freedml
12-18-2008, 11:02 AM
Ok, so a day or two of driving on each fuel should make it ready. In California they only test the fuel that the car is running on at the time of the test. Were they doing more extensive testing or does their computer only look at the gasoline computer? The original post doesn't say which state it's from.

nttrainer
12-18-2008, 11:07 AM
I don't know if all counties in Utah are requiring this but Utah County (where I live) is requiring that the emissions test be performed on BOTH fuels. They are also getting very picky about non-EPA approved systems.

kirkbenge
12-18-2008, 01:00 PM
... "You can drive all you want on CNG and some of the sensors (Evap Sys, Catalyst, O2 Sensor) won't go to ready until you drive on gasoline."

I don't want to sound too critical, but this statement cannot be true. As I stated previously, my '01 cavalier Fuel Sys, Comp, and 02 sensor were NOT READY. I had been driving normally on CNG for several hundred miles prior to this experience, but the codes were NOT ready. I did not switch to gasoline, instead I drove the car at a steady speed (I actually drove about 10 minutes at exactly 50mph, and about ten more at 55 mph) on CNG. When I got back to the I/M shop, all the codes were ready. I know from personal experience that the codes can all be ready even if you are only on CNG.

Something that I forgot to mention previously: When I returned to the shop after the drive, I did not shut off the car, but left it running until the tech checked it. My plan was that if it didn't work the second time, I would unplug the low pressure lock-off, run on gasoline for 20 minutes and come back later, but it never got to that, 'cause it worked even on CNG.

KIRK

Also, check out this post for what other people have said... http://cngchat.com/forum/showthread.php?t=2525&

Highmarker
12-18-2008, 03:02 PM
I had the same problem with my '01 Cavalier back in June. When you go for the emissions test, don't turn the car off. Just have it idling while you are waiting for them to do the test, then pull into the shop and tell the technician NOT to turn the car off. It worked for me.

nttrainer
12-18-2008, 03:27 PM
Kirk, I appreciate you sharing your experience. Sorry I got a little caught up in the hyperbole there.

My safety/emissions mechanic had a route of mixed driving that included about 10 miles of steady-speed freeway driving and returning on surface streets. He "guaranteed" that it would reset all sensors - it didn't.
I took the car to DMV's testing facility in Sandy (the buyer lived in SL County) and they ran it on their dyno for close to an hour and they said they were able to get the 02 and Catalyst to go ready but they would reset to not ready when the car was turned off. They only ran it on CNG.
I took it to Bill Brown Chevy in Provo and they tinkered with it for a week and couldn't figure anything out. They only charged me a diagnostic fee because they were so frustrated with it and just wanted it out of the shop.
We finally found the GM drive cycle and ran it through the cycle on both fuels and finally everything came ready. I have noticed this to be a particular problem with the '01 Cavaliers and to a lesser extent, the '02 Cavaliers. I haven't seen much of a problem with the '98-00 Cavaliers. No experience with '03 and newer.

It's nice to hear the experiences others have had.

nttrainer
12-19-2008, 08:10 AM
I had the same problem with my '01 Cavalier back in June. When you go for the emissions test, don't turn the car off. Just have it idling while you are waiting for them to do the test, then pull into the shop and tell the technician NOT to turn the car off. It worked for me.

That seems to be a common issue with the '01 Cavalier - the sensors reset when the car is turned off. That is what the Air Quality tech found with my car. He was running a real-time sensor on the car while it was on the dyno and he said that the sensors would go back to not ready when the car was turned off. Probably a good thing to remember when you take the car in for emissions testing.

Bear95
08-20-2009, 10:15 PM
Hello,

I have a Chevy Cavalier 2001 having the same problem now, wore is the fuse for the CNG. I can’t find it.
They say a message comes up “COMP” How do we fix that so My car a pass Emissions.

Thanks,

kirkbenge
09-01-2009, 10:30 AM
OK, so I'm due once again to register my vehicle, time to pass emissions testing. I took it to my local Jiffy Lube, after driving my usual complicated route (cold start, accelerating, holding 50 mph, then 55 mph, then coasting to 20 mph etc) and I told the tech NOT to turn off the engine, but he absolutely refused, so of course I failed; 5 codes not ready.
I hooked up my OBDII scan tool, and drove the route again (I wanted to verify that everything was READY), but to my surprise, no matter how long I drove, I could not get the EVAP and CATALYST to be READY. I kept my scan tool plugged in for two full days of driving, and both codes NEVER went to a READY state. I was getting frustrated, thinking I wouldn't be able to pass emissions, so I decided to call the number for the health department listed on the I/M report.

Guess what? The 2001 Chevy Cavalier Bi-fuel is on the EXEMPTION LIST! (in Salt Lake County)
It is a known issue that the codes reset and are very difficult to pass. You only need to do the tail-pipe sniffer test. When you go to your local I/M shop, tell them you need the tail-pipe test, and have them call the state at 801-313-6720 (salt lake county) for verification. No need to go through all of the hassle of getting all of those codes set!

I would assume that if this is a known issue, other states and counties have adopted similar exemption lists. I am in Salt Lake County.

wacbass
11-13-2009, 08:04 PM
Thanks so much for posting about the exemption!!! I have been wrestling with my 2001 Cavalier since first of Oct. trying to get it to pass. I will let you know what my local Jiffy Lube says.

nttrainer
11-15-2009, 10:41 AM
To bypass the OBDII test and do the tailpipe sniff they need to put in an exception code. The code is 201 (two-zero-one). At least that is what Utah County uses. I'm not sure if it is the same in the other counties.

niklan123
07-28-2010, 07:57 PM
I am new and I can not post a new thread and I need help. Please, Please. I have a 2001 Cavalier and went to Emmissions today and they have to test both Gasoline and on the CNG and it has to be right then and there. My car when it has CNG in it, runs on CNG and only after that is gone will it switch to Gasoline. Well I can't figure how to switch from CNG to gasoline and they don't know or care, and wont pass the car until I can show them how to do it. They wont let me come in on Gasoline and come back an hour later with CNG. Does anyone know how I can go to Emmissions and let them check the CNG and then know how I can make it run on Gasoline for there stupid test. It is so hot here in Arizona, and my wife spent 7 hours dealing with the most uncaring people in the world. Thank You so much for any help you can give.. Thank You Lanny

freedml
07-28-2010, 09:58 PM
Take it in running on CNG, then pull the Alt Fuel fuse in the engine compartment and it will switch to gasoline.

CNG Utah
07-29-2010, 01:01 PM
I think on an 01 Cavalier it will actually say CNG on the fuse box. It's probably a good idea to turn off the car before pulling the fuse.
http://www.cngutah.com/assets/cng-fuse.jpg

niklan123
07-29-2010, 07:22 PM
Thank You so much. 2 emmission places didn't know about the fuse, 3 Chevy places didn't know, searched the web for 6 hour's, paid $19.00 on Ask.com to Chevy Master mechanic and his suggestion was to time my visit to emmissions so the CNG would run out and the Gas wpould start up. LOL What a long day but today because of this Forum everything went so smooth. Thank You to Everyone