In this article we talk about how these components work and how to make a quick diagnosis.
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IAC 4-wire valves are small step motors, in this case it is bipolar type and ... it is clear that with this term I do not mean the volatile personality changes of some people. This type of engine became popular among car manufacturers due to the fact that the number of cables needed to control it was reduced and costs were reduced and therefore they were the perfect substitute for the old 5 or 6 cable valves.
In the previous figure you can see the various detachable parts of a valve IAC rod.
This is the rod that has a guide and at the end of this is the endless thread (it is not seen until it is removed).
The spring that maintains the torque on the stem so that the movement is stable.
The bipolar electric motor that is responsible for moving the endless stem forward or backward.
This valve is fed directly with 12V regulated by the car computer (ECU) and the control signals are of the binary type, that is, each terminal is powered or by 12V full or by 0V full (ground), there is no analog signal as This is the case of the TPS sensor. Below is the internal electrical connection of the two most common valves.
For all valves, the electrical diagram is the same, only the shape of the rod changes. Now, as I was commenting, the reduction of cables brings a problem for mechanics who do not have a standard OBD II scanner (you can send them command to move), since it is very difficult to move the valve engine entering signals manuals to their terminals as it was done with the 5 or 6 cables.
Let's see why, as I said at the beginning, these valves are of the bipolar type which in short means means that the movement is based on the manipulation of two magnetic fields that are supplied by two coils (that is why the 4 cables) then to make a full turn of the engine you have to enter the following sequence in its terminals.
When making a complete turn, the endless screw of the rod is moved out approximately 2 tenths (this measurement depends on the manufacturer) so to see perceptible movement this step must be repeated about 10 times.
The important thing to keep in mind with the input of these signals is that the power cut must be done in all equally, because for example if we are doing it by using suiches, and close and open one by one by sequence as we would be adding incorrect steps to the engine and it would never turn. This is why it is difficult to implement a mechanical system in the workshop to turn it around.
In these cases if you have a mechanical workshop or you are a user of a car that has this type of valves if I recommend the purchase of equipment dedicated to the operation of these as the Valve Tester IAC 4 cables. Why? From my own experience, 90% of the valves that have brought them to me have been recovered, and those that were not, were because they were forced and damaged or were opened for repair.
A diagnosis that can be carried out without the need for many equipment are:
1.-Insulation and resistance test:
For this you must know where the coils of it are. If you do not know the brand of the valve or the model is very different from the one shown in the figures above, you can identify the coils with the help of a multimeter.
The method is shown below:
1.- Place the multimeter on a 200 ohm scale.
2.- Place one tip in terminal A and the other one is placed in B, C and D. When at some point you give continuity of about 50 ohms, coil 1 has already been identified.
3.- Mark the points on a piece of paper.
4.- Now test the two missing terminals that in the previous process did not give continuity and verify that there are 50 ohms of resistance.
See the following figure that illustrates the steps, in this case continuity points A and C, B and D.
For this test lean on the previous figure. As you can see, the coils correspond to terminals AC and BD. Only the insulation test between the chassis (metallic part) and contacts that is shown in the following figure would be missing.
The following must be fulfilled:
The coil resistance must be between 30 ohms and 60 ohms: A lower value indicates that there was overheating and insulation is being lost, and if it is higher it indicates false coil contact. If you present these two problems it is recommended to replace it, it is not repairable.
The resistance between coil contacts must be infinite: A value below 100k ohms indicates insulation problems between coils due to overheating. In this case it is still possible to use the valve, but you must program your replacement in a short time.
Resistance between coils and the valve chassis must be infinite: A value below 100k ohms indicates insulation problems between the coil and the chassis due to overheating. In this case it is still possible to use the valve, but you must program your replacement in a short time.
1.-For the movement test I would suggest the following procedure: Remove the IAC valve from the acceleration body.
2.-Connect it to its connector.
3.-Pass the ignition switch to the ON position. (Ask someone else to help you do this step for you).
4.-While performing this step you should note that the stem of the IAC will come out approximately 4mm (depends on the engine manufacturer). This procedure is done by the engine to close the air inlet to the engine to start with more gasoline than oxygen (rich mixture).
5.-The next step is to bring the engine ignition switch back to the OFF position.
While performing this step you should note that the valve stem will return to its original position.
Pay attention to the movement of the valve, it should be smooth and free of blockages.
It is important that you perform the procedure without disconnecting the IAC from the power supply or de-calibrating it. Then the car will not start (if I leave it with a shank further out) or it will start accelerated (if I leave it with the shank further in).
Well, it's all for the moment, I'll talk later on how to perform maintenance on these components with the use of the tool.
To see what an IAC valve is, visit our article Valves IAC.
They fail because the air flow that they regulate passes through the stem and the spring of the same, creating turbulence. This causes that all the dirt and the residual coal of the combustion adhere to these parts; and with the reciprocating movement (Regular air intake to the motor), all this dirt enters the moving mechanical part inside the valve motor, clogging it.
The dirt also increases if it gives unnecessary accelerations to the engine. This is because the rich mixture produces a lot of ollin, and the high vacuum that occurs in the intake manifold when you stop accelerating the engine sucks all this dirt towards the valve.
These valves with routine maintenance can extend their useful life for more than 100 thousand kilometers; In fact, I had one that never changed for 6 years. That if ... once a month I took it out, to make maintenance.
Inevitably the valves are damaged by winding failures. As they are electric motors they can not escape their biggest enemy ... The temperature. The engine of a car is not to say a very cool environment ... then the high temperature degrades the insulation until it finally collapses.
The answer is yes, and it is simpler than many believe. Go to my article "How to make a homemade IAC Valve tester". Is very good.
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Written by Dennis García
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