As automotive technicians, we use a myriad of different devices to diagnose broken motor vehicles. Sometimes we use a divining rod, sometimes we use a sledge hammer, sometimes a chicken’s foot but mostly we use a scan tool! Providing, of course, that our magic wand is in for repair.
Often, however, when we use a scan tool we find that it does not report any fault codes. It’s obvious the car has problems! We can feel and hear engine misfires. We can see smoke coming out everywhere. We know by the sheer temperature of the engine bay that the catalytic converter is on fire!!!
So how can there be NO fault codes?
As you may already know, on many late model cars if an individual module (ECM, TCM, etc.) is not “talking”, it will not and cannot report any issues. It simply doesn’t communicate. This is particularly common on European cars, BMW for example. With many scan tools, after running a preliminary scan of the vehicle, a technician can find a “communicating modules” section. Alternatively, by reading the quick scan results, the tech can determine that he or she doesn’t see all the modules necessary to operate the vehicle correctly.
Suppose I find that one or more modules are not talking. Why? Why, I wonder, is this happening to me? Modern cars are extremely advanced; the headaches they cause will never disappoint me. Does it want to torture me? Or could it be because something happened to the vehicle before I ever touched it? Perhaps the customer “forgot” to tell me that the battery went dead and he had a friend jump start it in the Sears parking lot. Or maybe a set of incredibly huge speakers were installed, (complete with a bowel shaking 1000-watt amplifier) with no regard to how the bus systems work.
These are just a few of the ways to completely collapse a CAN network or bus system needed to allow electronics modules to communicate.
Whatever will I do?
Before you throw your shoe at the car and run away crying, try something as simple as ……………….a battery reset!
Yep, this little bit of magic is a good way to jump start a confused CAN network that has been traumatized by ineptitude.
Simply remove the battery cables from the battery. Touch the cables together. (European cars require a long mating period, typically no less than fifteen minutes.) After a while refit the battery cables (positive first) and run another scan. You will most likely see a ton of faults codes appear, where they did not exist earlier.
Now you can stand tall and proud, hair combed neatly and teeth brushed, knowing you have conquered the faultless phenomenon.
Who needs college?
TECH TIP 101:
Fully charge and load test the battery while you have the cables off.