: Failed Emissions Test- But No Codes

12-27-05, 01:19 PM
Ok here in Central Texas they have added the dreaded emissions test to the annual inspection. My car has no codes. No MIL light. They don't sniff ODBII cars here but hook up and do a systems ready test. Apparently the system said the Cat was not ready, Evap not ready and EGR sys not ready. There are 9 things they check and you are allowed only 2 not readys I had three.
Car runs great. The inspector said it might have something to do with drive cycles?? I reset the PCW about 2 days ago. He said I should drive it more and bring it back..LOL
So what sre the drive cycles for the Northstar after reseting the PCM. ANd could it be I didn;t drive it long enough this morning before I went??

12-27-05, 01:52 PM
You're on the right track. Try this. http://www.obdii.com/drivecycle.html

12-27-05, 02:14 PM
did you even warm it up?

12-27-05, 03:02 PM
dkozloski - thanks for the link.
That the link that had found also.
I was able to find it about 5 minutes after I posted this :rolleyes:

eldorado1 - yeah the car was definitely warmed up. I imagine that I haven't driven enough cycles to clear all rediness flags. I 'll guess I will drive it around the rest of the week and try again on friday. You get two chances at the test before you have to pay again :thumbsup: I didn;t realize it can take up to 5 driving cycles to determine the state of the cat.

I will also have to assume that somewhere in normal driving ; a driving cycle will be completed.
You would look like an idiot doing the requested drive cycle operation 5 times. I'm sure that the explanation is the way to do it in about 20 minutes or so.

Anyway thanks for the info guys :)

12-27-05, 05:23 PM
A drive cycle consists of a very specific set of criteria.
There are a couple hundred codes that can set in your engine operating system. Each code has a set of conditions that must be met before the diagnostics can be run. A drive cycle would be a trip that consisted of all the criteria being met for each code to run. Those are few and far between, let me tell you.

What he is looking at are called "flags", basically they are flags that indicate whether or not certain system tests have run and passed. For example the O2 sensor system is monitored for several criteria including time to activity along with switching voltage signals and good pre and post catalyst readings. If all the temperature, time and data is correct the computer sets a "flag" to tell the computer that the O2 sensor system is operating normally.
There are several flags for different systems.
When you cleared the codes, you reset the flags all to "not run".
The machine he hooks it to tells him that not enough flags have set so that he can pass the car on the emissions test. You have to drive it for a few days so that all the flags will set because all the diagnostic tests have to run and pass. This is supposed to prevent people from clearing the codes right before they go get a test and pass because the CEL is not on (MIL).
This way the tests have to run AND pass before you can pass your test.
You are given a margin of 2 flags that don't have to be set, meaning not ALL of the test have to run but most of them do.

Just drive it for a few days, do some highway driving if can, and then take it back. Don't clear the codes again or you'll be right back where you started.

12-27-05, 05:33 PM
Here is an article I found online that might clarify a little bit.

Final quality check: a drive cycle provides the key component to OBD II system repairs: the final check on repair quality
Motor Age, Jan, 2005 by Stan Stephenson

The On-Board Diagnostic (OBD) II system, since its full introduction in 1996 vehicles, has completely changed the way technicians now must approach emission system diagnostics. On today's vehicles, 17 or more separate subsystems are monitored by OBD II. Also, as many as 11 monitored circuits check on the OBD II system's running condition. The former Check Engine light has now become a Malfunction Indicator Lamp (MIL).

As the OBD II system runs its checks on these individual monitored circuits, it will illuminate the MIL to advise the driver or technician of the need for service before performance deterioration of a component results in total and possibly expensive failure of the system or component.

The complexity of problems detected by the OBD II system in late-model vehicles is seldom confined to just one subsystem that may be in need of repair. Issues of readiness monitors, analysis of diagnostic trouble codes (DTCs) and running a drive cycle all play an important part in turning off that MIL--and keeping it off.


To make this happen, OBD II runs a complex series of algorithms--programmed mathematical comparisons continuously on some circuits, periodically on others. The system will illuminate the MIL whenever a monitored circuit indicates any of the emissions gases is likely to exceed 150 percent of the design standard.


Even if the MIL is off, there are two problematic issues in OBD II emissions testing today. One is a vehicle's readiness to take a test. The other is in performing a drive cycle to ready it for a test and to provide a quality check on the work performed, including a check that the MIL is out and stays out after the repair.

In some states, any vehicle submitted for an OBD II emissions test must be tested as presented--whether the MIL is on or not. If the vehicle fails because the MIL is on and it is not ready to take the test in the first place, repairs must be made up to at least the dollar-value of the waiver limit of that state.

Readiness, of course, applies to the 11 monitors of the OBD II system. Three of these are continuous monitors that run all the time. The other eight monitors run intermittently. For OBD II-equipped vehicles, most states follow the U.S. Environmental Protection Agency's (EPA) guidance on unset monitors. This allows for two monitors to be unset or not ready in 1996 to 2000 model-year vehicles. Vehicles from 2001 to the current model-year are allowed only one monitor unset or not ready.

Today, many vehicle owners do not understand why their vehicles may not be ready to take an emissions test. For the shop owner, the difficulty lies in explaining the problem to an owner who feels his or her vehicle is operating fine: "So what do you mean it isn't ready to take the test?"

Failure to heed an illuminated MIL because the vehicle seems to operate normally could mean an expensive failure. In cases of any monitor being unset or not ready, the MIL will not always light up immediately to alert the owner that something must be checked.

Some motorists, and even some techs, believe that disconnecting the battery for a few seconds will turn off the MIL. What this actually does is cause all monitors to become unset or not ready. The only tiling that will reset the monitors, or at least the ones that were ready, is to perform a drive cycle. However, the chances of performing a successful drive cycle are slim, especially if the problem has not been diagnosed and repaired correctly.


An important part of an OBD repair technician's toolbox is the comprehensive drive cycle manual; the only source is published by Motor Manuals. The latest 1996-2004 edition contains just more than 900 individually different drive cycles for the wide range of engines now in use. Contrary to what many technicians believe, there is no generic drive cycle. A technician also needs a reference book that covers all the many DTCs. At last count, there were well over 800 of them, and that number grows each model year.

Unfortunately, there is no indicator that points to exactly which monitors may be either set to ready or be unset and not ready. Some late-model vehicles have a driver indication about a state of unreadiness, but there is no indication as to which monitor or monitors are affected. At this point, DTCs will have to be revealed to determine exactly what part of the emissions control system needs to be serviced.


Today one of the most difficult areas of OBD control to tackle is proving to be the evaporative fuel vapor control system (EVAP). That EVAP monitor's state of unreadiness must be corrected, and getting this monitor to run is proving to be an involved part of OBD technology--so much so that is creating a need for specialized training on the diagnosis and correction of EVAP problems.

Despite its complexity, the OBD II system's MIL is most often illuminated because of simple stuff: loose connections, a broken wire or, in the case of an EVAP code, probably a loose gas cap. An EVAP monitor check also calls for the fuel tank to be filled no less than one-quarter and no more than three-quarters.

Now, about that gas cap: Many motorists simply fail to turn the cap the recommended three hard clicks to properly secure it. But in some very late-model vehicles, the new style of screw-on gas cap does not crick itself into a secure position. In the case of a vehicle owner who suffers from arthritis, that final gas-cap click or screw home may be impossible.


Post-repair drive cycles pose their own set of problems. Several steps must be accomplished to satisfy the OEM's specific enabling criteria and achieve a monitor's state of readiness. All these criteria differ from one vehicle make to another, and even within some engines of an OEM's line there is little commonality. So enabling criteria for any given monitor may differ. Enabling criteria for specific monitors can be found in the drive cycle reference guide.

While each OEM's drive cycle is different, let's look at a general example of what procedures could be involved in performing a typical drive cycle. It is important to note that this is not a specific drive cycle, it is an example of what one may involve.

First, the vehicle should be warmed up to operating temperature, and then accelerated up to a steady speed of about 30 to 35 mph. Next, the vehicle must be allowed to come to a complete stop without ally brake application. After that step is complete, the vehicle should be accelerated to about 50 to 55 mph for a specified number of minutes, and then be allowed to coast to a stop--no braking.

These steps, when performed correctly, complete the drive cycle, set all monitors to ready and turn off the MIL.

The difficulty with miming any specific drive cycle is likely to be in finding a stretch of road, especially in areas with large populations, to do all this accelerating, cruising and slowing down as prescribed. Some believe they can simulate a drive cycle on a two-wheel ASM dynamometer, but others in the industry say dais is not possible. A four-wheel dyno could do a drive cycle if the operator follows the OEM's prescribed routine exactly, but it is often tough to do.

At least one late-model General Motors 3.6-liter V6 engine is not so easy to run through a drive cycle as described above. That engine may have to go through as many as three cold-soak routines over a couple of days in order to accomplish its exact drive cycle as specified.


For virtually all drive cycles, the automakers' instructions state that two people should take the vehicle on a checkout run: One to drive the vehicle, and the other to read the drive cycle instructions. This OEM recommendation is made to cover any questions of subsequent liability.

Of course, this raises the question for the shop owner of how much to charge to perform a drive cycle, especially if two techs have to make the run according to the OEM's recommendations. Diagnostic time is not cheap, nor is shop labor time.

Some shop owners believe they can ease the complexity of running a drive cycle by giving the vehicle owner a copy of the vehicle's drive cycle and the advice to follow the instructions. This is a very bad idea. If the vehicle owner has an accident because he/she was reading the instructions you gave them instead of paying attention to the traffic, you and your shop could be liable.


Perhaps what is needed on rite part of all emissions test/repair shop owners is to accept the reality that running a drive cycle is a normal part of an OBD emissions repair. It should be listed and billed on the work order.

12-28-05, 01:22 AM
I don't get this one: the vehicle should be accelerated to about 50 to 55 mph for a specified number of minutes, and then be allowed to coast to a stop--no braking.

How can a car with an automatic transmission "coast to full stop"?! That is impossible unless you happen to be going up a hill! When the car is in 'Drive", it'll never coast to a full stop on a flat road.
At least none of the automatic transmission cars I owned.


12-28-05, 06:54 AM
On IM/240 tests and some OBD emissions tests they do that kind of thing on the dynomometer. In VA where I am we have a dyno-test for emissions.
It tests the car on a drive cycle for tailpipe emissions and checks the readiness flags. The car should be "pre-conditioned" so the catalyst is ready and some other things are good to go on the dyno.
It's really hard to do some of these tests.
The CA "smog" program is very similar.

Jack Ammann
12-28-05, 07:54 AM
Ok here in Central Texas they have added the dreaded emissions test to the annual inspection.

The best technique I have found is to "befriend" an inspection tech. AND I don't even have a Catalytic Converter...LOL. **I took it off right after he inspected the car**

:lies: :eek: :bigroll: :thumbsup: :highfive: :rolleyes:

12-28-05, 08:11 AM
The best technique I have found is to "befriend" an inspection tech. AND I don't even have a Catalytic Converter...LOL. **I took it off right after he inspected the car**
:lies: :eek: :bigroll: :thumbsup: :highfive: :rolleyes:
They have always checked for Cats here. The problem is the EPA readiness checks that the PCM will report to the Emissions testing system. Here in my county, they only check these flags and the MIL for cars with the ODBII, for earlier cars they use the tailpipe emissions probe. Jack I like the idea of befriending a "TECH", this at least hopefully the tech would have AutoXray or something similiar to check those damn ready flags before you go.

ewill3rd- thanks for the info. Since some of these readiness flags are based on a specific driving arrangement and sequence, it would seem that it is possible that some of these flag will never set to ready until you do the exact driving sequence required. Utterly ridiculous in my book. :rolleyes:

Peteski - your right about the complete stop with an automatic car, however I'm wondering if the parking brake would be considered a braking, point being as you approach a slow roll ease into the parking brake. Anyway go figure that these drive cycles seem to have little to do with a "REAL WORLD" drive cycle. The F****** EPA should be worried about what happens under normal driving conditions and not when eveyone is carpooling doing a readiness check as they go to work...LOL

BTW : I have driven this car 2 days ago on a 300 + mile highway round trip with a 24 hour stop in the middle of that trip. You'd think the damn flags would have set by now...

12-28-05, 09:59 AM
It obviously gets complicated but some tests only run under certain conditions, it's almost impossible to complete a "drive cycle" in one trip because some of the enable criteria are way to complicated to duplicate with any degree of accuracy.
I'll know there is a document that outlines a "drive cycle" but I don't recall where to find it.
What year is your STS and I'll see if I can find the drive cycle criteria?

Here is an example of information on the readiness flag for the O2 sensor system.

Inspection Maintenance (I/M) program
Several states require that vehicles pass OBD system l/M emissions inspection. These inspections may apply to any 1996 and newer model year OBD II equipped passenger cars and light duty trucks.

As part of an OBD I/M emission inspection, the vehicle's I/M readiness status is checked to ensure that the vehicle's OBD system has properly evaluated the emissions systems of the vehicle for proper operation. To ensure vehicles are capable of passing this portion of the inspection, technicians can review the l/M readiness test status using the l/M System Status display on the Tech®2. This display provides test data that will verify whether the vehicle's OBD systems have run. States performing inspections on an advisory basis will not reject vehicles for not being I/M-ready.

Conditions for Updating the I/M System Status
Each OBD II system requires at least one diagnostic test. A system monitor is complete when all of the DTCs that report to the system monitor have run and passed or failed. The results of a failed test are reported by a diagnostic trouble code (DTC).

Once all of the tests are complete, the l/M System Status display indicates YES in the "Completed" column. For example, when the HO2S Heater Test indicates YES, all oxygen sensor heaters have been diagnosed.

When any required test for a specified system has not run, the "Completed" column under l/M System Status displays NO. The following is a list of conditions that would set the l/M System Status indicator to NO:

• The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.

• The battery has been disconnected or discharged below operating voltage.

• The control module power or ground has been interrupted.

• The control module has been reprogrammed.

• The control module DTCs have been cleared as part of a service procedure.

Monitored Emission Control Systems
The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with AIR or EGR.

The following is a complete list of the vehicle's systems that may require monitoring by the OBD system:

• Air conditioning system

• Catalytic converter efficiency

• Comprehensive component monitoring (emission-related inputs and outputs)

• Evaporative Emissions (EVAP) system

• Exhaust Gas Recirculation (EGR) system

• Fuel delivery system

• Heated catalyst monitoring

• Misfire monitoring

• Oxygen sensor system (O2S or HO2S)

• Oxygen sensor heater system (HO2S heater)

• Secondary Air Injection (AIR] system

If a specific vehicle is not required to monitor one or more of the above listed systems, the Tech®2 display will read "not supported." Any non-supported system will not be considered when determining the readiness of the overall system.

For the specific DTCs related to each system, refer to SI (Service Information) for further diagnostic information on conditions for running the DTC or refer to the publication information mentioned in this bulletin to order the Inspection Maintenance Emissions Diagnostics Manual and follow the I/M Readiness Testing System DTC Tables. Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles any may not require an indicator.

12-28-05, 10:18 AM
dkozloski posted this earlier in the thread

Try this. http://www.obdii.com/drivecycle.html

I just think its asinine for the car not have ready flags turned after 400 miles of driving most highway some city and under different conditions. I guess I'll wake up early in the mornings the rest of the week and do the drive cycle described above. LOL..... sorry officer I can't maintain a constant speed due to these drive cycle instructions.... I'll have the emissions report handy, drive cycle instructions and stop watch in hand just in case he thinks I'm drunk :alchi:

12-28-05, 11:53 AM
If you have a document that shows you failed the test you should be okay to drive it for a few days, at least in most states, they give you some time to get it done.
Also remember I think they give you 2 flags that don't have to be set.
Just don't let the battery go dead!

12-28-05, 01:22 PM
This business of "befriending a tech" can escalate to a federal felony if you're not careful. Why not just pay the money like everybody else.