In the 80’s it was said that ECMs using OBD (On board diagnostics) would put technicians out of a job. A computer would do the task of diagnostics and it would do everything to fix itself besides turn a wrench. How did that work out? Technology is supposed to make life easier and simpler but when you compare a new ISX to an old beige big cam do things look simpler and easier? ECMs all have an on board diagnostics system. Is it useful? Absolutely. Is it perfect? Not even close. I hear lots of guys refer to the ECM as the brain box. Take it from someone who has disassembled hundreds and programmed thousands…there is no brain in there. The diagnostic systems on ECMs are more limited than most people realize. That’s why the need for technicians who use their head to find problems in this industry has never been greater. I’ve worked alongside great technicians and I’ve worked with guys who just pull codes and change parts. The difference tends to be if they are using their brain or not.
Do you need a computer to tell you that you have a miss? If you know your truck you don’t. You can hear it, you can feel it, and you know something isn’t right. A parts changer isn’t going to be interested in talking to you. He’s going to plug in, pull codes, and basically do what the computer tells him to do. If the computer doesn’t tell him what’s wrong or he changes it out for his test DDEC III with tons of timing advance in it then he will say the ECM is bad and change the computer because that’s what parts changers do. There is a lot of profit in the parts business so there isn’t much corporate incentive to change this. Also good technicians are expensive, hard to replace, and increasingly hard to find. Many are from before the days when there was an ECM on the engine. These guys had to rely on their eyes, ears, a toolbox full of testing equipment and their brain to find problems. The best techs out there combine their knowledge with the diagnostic information from the ECM. They realize that the ECM’s diagnostics has limitations and they don’t let it do the thinking for them. Imagine you have a DDEC IV that won’t start. Most of the time a DDEC IV will not log a code in this situation. If a DDEC IV loses unswitched power, the ignition input, or both timing signals no fault code will be logged. If it’s power related it won’t communicate. Also Series 60 engines with DDECIVs do not have a fuel pressure sensor. A technician will know what fuel pressure was when he tried to crank the engine. If the engine didn’t have an ECM the fuel pressure would be the first thing checked in a no start situation. A parts changer who relies on the ECM to do his thinking isn’t going to know what the fuel pressure is. Check back next month for the next part of this article.
Written by Fernando DeMoura, Diesel Control Service LLC.