As most are aware, a transmission is not just a transmission anymore, in fact it has not been a stand-alone component for several decades now. A lot of the discussions I get involved in these days have to do with issues outside of the transmission which manifest themselves as transmission problems. This may be electrical issues, drivability related issues or even issues such as DTC’s setting in other modules that appear to be causing problems with transmission operation. The transmission is part of a complete system which is interwoven with other vehicle systems to make vehicle operation transparent to the operator. Just like your own body, if one of your primary organs is not working quite right it can raise havoc with your other organs which can have a dramatic impact on your body and its overall health.
A lot of things have changed over the years and operation of the vehicles you repair every day have also dramatically changed. The advent of OBD II in 1996 really started the ball rolling in the direction we are moving today. OBD II was designed to enhance the ability of the vehicle to make sure the systems-maintained emissions compliance during their operational life time.
One area that was added with the advent of OBD II was diagnostics known as I/M (Inspection and Maintenance) flags or I/M Readiness monitors. The whole idea at the time was to give the folks at your emissions testing facility an easy way to determine if your vehicle was emissions compliant or not. The problem with the design was that some people figured out ways around the system so the vehicle could be licensed even though it may not be emissions compliant at the time.
So, this leads us to where we are today. You just stepped off the tool truck where you laid down 5+ grand for the latest and greatest scan tool available. Being excited to try out your new toy, you plug it into a vehicle and attempt to clear the DTC’s which are set. Now you are confident that the repair you had just finished should have addressed the issue with the DTC so you hit the clear ALL DTC’s button. The scanner indicates that all the DTC’s are cleared so you fire the vehicle up for your test drive. But before you can even get out of the shop the ‘check engine light” is back on and you find that you still have a DTC set. So, what should you do? Chase the tool truck down the road so you can tell him what you think of his latest tool? Send it to the dealer so they can clear the DTC with their factory scan tool? The answer is no to both of those solutions.
As was stated earlier, vehicle systems are in a permanent state of change and we all must adapt to those constant changes. Starting around the 2010 model year manufactures started to change the way the I/M flags and DTC’s function. Some DTC’s are now classified as “Permanent DTC’s”. Permanent DTC’s are now programmed into various vehicle modules not just the PCM/ECM. This means those DTC’s cannot be cleared by disconnecting power or even with the factory scan tools. The whole idea was to eliminate the situation where the customer either purchased a cheap code clearing tool or took the car to his buddy to have the code cleared prior to taking it in for the emissions test.
So, the question is what do you do now? Resetting the I/M flags and clearing the DTC can only be accomplished by operating the vehicle to allow the system to operate and test the component/circuit in question. If the controller is happy with the test and the ignition has then been cycled to the OFF position, the light and DTC will disappear by themselves, if not the problem will remain and you will need to further address it. With your scan tool attached, you should be able to monitor each of the I/M flags so you will know when the test was complete as well as the tool should give you information on if it passed or failed the test.
The key to the vehicle testing of the I/M flag components is to follow a specific test-driving process. The problem with this process is that it is not standardized across the manufactures, in fact is it not even standardized within most of a manufacturer’s vehicle platforms. This means the process could be different if you are working with a 5.3L gas engine versus a 2.7L gas engine even if both were built by the same company.
Today, information is king in our industry and this is no different so you will need access to a shop manual for the application to locate the process that must be followed. This process is typically called a drive cycle or I/M reset procedure. During your testing, your scan tool will typically be able to display parameters related to the I/M flags so you can monitor the progress. Once all of the tests have been run and passed, eliminating the DTC and light is as simple as turning the key off when the process is complete.
I have seen a lot of folks chase their tales on this issue so now that you understand what is happening you can be a hero to the customer that has had it to 3 different shops for the concern. In addition, you can set back with a smile on your face as your new 5000.00 is working just as it was designed to.
Until next time, remember “Nothing will work, unless you do”.