So, let’s talk about performance and what it means. First, what’s your objective? Are you racing the quarter mile? Or are you looking at something for the circle track? Maybe it’s off-road? Do we want our vehicles to get 27mpg in the city and 45 on the highway?
We have been working on cars most of our lives and have encountered numerous issues with performance. Whether it’s a code on a truck or automobile, it will always come down to the same expectation, and it is not working properly. Sometimes the issues may be intermittent or happen once or twice a week.
Yes, the check engine light comes on (according to the owner), but it is not on now when the vehicle shows up at the shop. It is time to play Sherlock Holmes. Is there any other way to describe this situation? We have no codes, nor do we have a shred of evidence now. The only thing you have is a customer telling you the vehicle has a problem and is not working properly.
Now in my book, I would first drive the vehicle stone cold, like first thing in the morning. Before starting the engine, I’d popped the hood open and visually check the battery terminals (Figure 1). Are they corroded? That will start a proper diagnosis when you are looking for a ghost in the vehicle.
Then we will install the DVOM on the battery. Let’s check the battery voltage before we even crank the engine. Then we check the voltage while cranking the engine to start it up (Figure 2). Is it falling below 10.5 volts? Because if it does, we have a problem. Sometimes when you check the voltage across the battery terminal, you’ll get one reading, but if you pinch the battery cable, you’ll get a different reading because of a voltage drop across, bad connections on the terminals to cables crimp.
When we are working on computer control electronic transmissions, voltage is as critical as ground, and I mean this to the last half of a volt. When the vehicle starts, and while cranking, the ignition is on feeding voltage to all the computers and sensors, every component needs to have the appropriate voltage it was designed to operate with, or functionality and performance are out the window.
One of the most important parts of this puzzle is getting the right information from the customer and when it happens. Mornings, afternoons, when it sits for a while, or when it rains? Yes, I’ve seen water run down a filler tube or a cowl and fill a connector or computer full of water and cause chaos.
A voltage drop is as devastating as a bad ground. Taking the time to diagnose and ask questions could save a lot of repair time. And maybe, just maybe, being able to fix and correct a problem that no one else could find and fix. That is a good feeling of self-accomplishment when you can find and repair an issue in record time.
On so many occasions, I have checked a circuit with DVOM and seen computer drivers not ground a solenoid properly and the transmission not shift, even though the computer calls for the shift. Without the proper ground circuit, the solenoid will not fire, and no shift occurs. The same goes for a lack of voltage to or from the computer. Remember that computers are dumb. If there is a lack of voltage or ground on a particular circuit, the computer will not “code” the circuit because it still sees a signal and does not recognize a fault.
Computers can only see open or short circuits to ground or power. Computers in trucks and cars cannot tell the difference if the circuit has the proper amount of voltage necessary to operate that circuit; it is just going to react to it. So, to be a good diagnostician, always remember that everything starts at the battery and ends up at the battery to complete a circuit to operate any component. Get to know your DVOM or Oscilloscope. Play with it to learn how to get the most out of it and get the performance you’re looking for.
