Has this ever happened to you?
Has this ever happened to you? You have just done some repairs on a vehicle and had fixed a check engine light (CEL) that had set a P0300 misfire code. The vehicle ran great when you were done. The owner picked up the vehicle after paying his bill and all was well until.... the CEL came back on. There was the usual phone call that they had just spent all this money to have that light turned off and now it’s back on again. What do you do? Have them bring it back if they haven’t already shown up; you pull the tech off the job they were doing to come over and rescan the vehicle to find a totally unrelated code. The customer really doesn’t know the difference but you do (say a P0420 cat efficiency code shows up now). How could you have maybe avoided this problem? Well you could have used Mode $06. Mode $06 has been around for quite a while (phasing in started in 94) but it has really not been used much or really grasped by the average tech. Mode $06 looks really complicated, gives the illusion of being a foreign language (Hexadecimal numbers),and it was really hard to find any information on it at all. Although most of this is true it has been made much more user friendly with the mandating of CAN. Mode $06 is one of 15 OBDll modes that are reserved for global diagnostic scan tool operation. It was designed by engineers for engineers to diagnose specific emission related failures. That explains why it’s complicated. Those failures are on the OBDll NON COUNTINUOUSLY monitored systems, this is important to understand. Basically vehicles with OBDll have 2 types of emission monitors, continuous and non continuous. A monitor is just a test or a series of tests that are ran on system, sub system or component to verify its operation. The difference in the monitors is really in the name but a quick way to tell is in how they set trouble codes. First a non continuous test only runs once per drive cycle, second almost all non continuous monitors use a 2 trip consecutive failure to turn on the CEL. This is where the rules get bent a bit, Ford reports their misfire data in Mode $06 which is really useful but is the results of a continuous test. A continuous monitor is testing all the time as long as conditions are met, such as MISFIRE, FUELTRIM, and COMPREHENSIVE COMPONENT it’s always looking for a failure and won’t wait until it sees the problem twice. The non continuous monitors only run when all of their enable conditions have been met, this is a key point. For the vehicle to perform a test on itself a lot of conditions have to be just right or the test can’t happen and this list of conditions is very vehicle/engine specific. What we need to look at is the fact that if there is problem in another system or another monitor has not passed it can disable the testing of many if not all the non continuous monitors. Some vehicles only need the CEL on and no non continuous monitor will run. The list of these enabling and disabling criteria can be found at your diagnostic information site or the factory website. The list of NON COUNTIOUS MONITORS is large and growing as systems are added that affect emissions. I have found 22 now (I am sure there are more) but the big ones that usually bite us are EGR, EVAP, CAT, AIR and Thermostat. When all of the conditions have been met and the PCM decides that the time is right to perform a test, it will run the monitor. When it’s done it will post the results of those test/tests in Mode $06. This data is kept here until another test is done and the data is updated or the data is erased usually by simply clearing a code. We can see these results if we attach a scanner and look at the Mode $06 data. This is the nice part, the scanner only has to be able to get us the generic side; we don’t need a factory scanner. Some factory scanners don’t even show Mode $06, (Tech2). This is the point that things can get difficult if not outright hard. You see the PCM is using binary numbers and when it reports that info to us in Mode $06 it uses hexadecimal numbers. Once the PCM sends out the results of the Mode $06 data in Hex form a couple of things can happen, the scanner will give us exactly what the PCM saw raw; hex values or the scanner may perform the mathematical operation of conversion for us and give us the decimal numbers that we are VERY used to seeing. Confused yet? well it is fuzzy let’s try and clear it up. Binary is the base of 2, Hexadecimal is the base of 16 and what we like to see is decimal a base of 10.When ever you see a number that is preceded by a $ sign on your scanner the value that follows is going to be Hexadecimal number format, because the system is based on 16 they use the letters A B C D E F along with 0 to 9 so you can see a number like $4FFE. This is 20478 I will explain how to get this number in a minute. So now we have our scanner hooked up and we are trying to look at the Mode $06 data and we see the report and it may look like this on a 2001 Honda: TID $05 CID $81 Min Value $100 Max Value $1F4 Current Value $1F3 When you see data like this the first thing you will think is WHAT THE HECK? What do these numbers mean? and what is a TID or a CID? Well let me give you some more information. First the data you are seeing is in HEX($), we will need to convert this. Second we will need to go to our information service to find out what monitor the TID and CID relate too. The TID is the Test ID (really the monitor); the CID is the Component ID (what we are testing). Before the implementation of CAN the manufactures were allowed to set the TID’s and CID’s as they wanted. After CAN they have rules and new names we now have MID’s and TID’s. MID’s are monitor ID’s they are standard across all manufactures and are now arranged in order of priority (o2 monitors first). TID’s are test ID’s and these can still be set by the manufacture as they wish. Getting back to our example of: TID $05 CID $81 Min Value $100 Max Value $1F4 Current Value $1F3 After visiting or information service we can say that we are looking at the CAT monitor for this Honda(TID$05 CID $81). We will need to convert the raw HEX numbers into something that makes sense to us. If you have access to a windows based PC then use its built in HEX to decimal scientific conversion calculator. Its in programs under accesories, type in the HEX value then hit the DEC button and the number is now in decimal format. Put those numbers into the data so it would look like this; TID $05 CID $81 Min Value 256 Max Value 500 Current Value $499 Now we are starting to see something that is of value to us, this car is on the verge of failing this test, the result is 499 and the max limit is 500. It is really close to setting a P0420 code and if the next test is above the limit it will set a pending code and if the next test after that is also a fail, the CEL will come on. Remember it needs two consecutive failures to turn on the CEL on a non continous monitor. One more thing that is VERY IMPORTANT this test/monitor will not run if there are any misfire codes (we saw this on our information site) and we had a P0300. This monitor was shut off and after our repair it was able to run again and it did twice, failing both times, turning on the CEL and setting the code. It sure would have been nice if we had looked at these Mode $06 values and test results before we had cleared the codes after repairing the misfire wouldn’t it.We could have made a note on the invoice and explained the situation to the customer before they left. It takes a little of the pressure off the tech when the CEL comes back on and you can say “we warned you about that, it may require more diagnostic’s ”. Written by: Jeff Taylor
Subscribe to comments