Understanding Basic Actuator Components

Ultimately, an actuator of any kind, be it a door lock, or an EGR valve, functions on the same principle. The specifics may become more or less complex or complicated, but ultimately it is the same principle. The minimum components are simple, a power source, a cable or wire to a switch or control of some kind, an electric magnet, and a return to ground. Somewhere in all of this should be a protection device like a fuse.

Where an actuator gets more complicated is when there are multiple inputs to a control to activate the actuator. Think of how a temperature sensor will send information to an engine ECU (computer) which will check with other parameters (like the air conditioning system) to send power to a valve which, once powered, opens allowing air to go through, activating the fan clutch. Once the parameters have changed and the ECU decides the actuator should close, the power is removed from the air valve, and the internal spring closes the valve, shutting the supply of air to the fan clutch.

Breaking Down the Components

In a previous article, I talked about the ingredients and steps to diagnosing a component failure. Let’s use this model to break down how we can diagnose an actuator, no matter what kind. For this, we’ll use a simpler example, a light. In the case of a light, you will have the power source, the cable going to the fuse box, a wire coming from the fuse box to the switch, then a wire to the light, and a wire to ground (back to the battery completing the circuit). If the light is no longer working you could just replace the light. Much better would be to verify the power coming in, and the ground on the other side.

If you didn’t have a ground, you might get away with easily finding or replacing the ground and be fine. If you don’t have power, you would check the fuse, the battery and then the wires or cables to verify if there is power and that the power can make it to the switch, then the light. To verify the switch is the same as the light: check the power coming in, and the ground/continuance on the other side.

The difference between a lightbulb and an actuator is that a lightbulb often burns out or a filament breaks. An actuator can be much more uncertain. Maybe the valve seems to work, but it doesn’t open all the way or close all the way. Maybe it’s out of adjustment and is letting more or less of a fluid, air, or exhaust through.

Breaking Down the Actuator

Let’s assume we know the actuator has power, the signal gets to the actuator to tell it when to work and maybe how much to work, or which direction, and the ground is also good. Pretty much any actuator on a truck or trailer can be activated safely on a bench, but when something is rotational like a starter or moves aggressively you want to make sure it’s well secured. If it requires lubrification or cooling you also want to make sure you can handle that. Otherwise, any actuator can be verified on a bench, off the vehicle. It’s just usually easier when installed.

In every electric actuator, an electromagnet will be created by the signal/power. For an actuator to be able to do this, there needs to be a resistance. Ideally, you verify this resistance to a known specification. You can, however, verify the resistance versus a new part without installing the new part to see if it solves the problem. Electric components are usually hard to return if you can at all, and you don’t know that the power or ground caused the magnet to fail in the first place. If this is the case, it will damage the new part as well. Even just with experience, you can often have an idea if a resistance is reasonable, much like with a sensor.

Another thing you can check with or without diagnostic literature is the operation of the actuator. Does it normally, or would you expect it to normally be quiet? Is there an abnormal vibration? Many actuators will have a certain vibration while working, is this one unreasonable or unexpected? It may be a problem. Is the function supposed to be smooth but now pulsating? Again this could be a problem with the power source or ground (wiring or battery). Don’t forget that an ECU or other controller could control an actuator by the power, ground, or both!

Conclusion

All these things are reasonable for a fairly competent mechanic to verify even diagnostic information. Of course, knowing exactly what to look for and having a list of tests laid out for you is nice, but be careful what you wish for. In the other extreme of having no information is having too much. Some manufacturers demand that you follow their tests and verifications despite any evidence clearly signaling to you what the problem is. While this isn’t necessarily your problem, only the manufacturers, it's still something worth keeping in mind.