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Re: Voltage range for IAC operation on a B202L
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Posted by Gene N [Email] (#1094) [Profile/Gallery] (more from Gene N) on Wed, 2 Jun 2010 04:55:37 Share Post by Email
In Reply to: Voltage range for IAC operation on a B202L, Kevin M [Profile/Gallery] , Tue, 1 Jun 2010 17:20:34
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Ah, not quite that simple. The signal to the IAC is actually Pulse Width Modulated (PWM). What does that mean? It means that the current to the IAC is being continuously turned on and off at, usually, a set frequency and the difference between the time-on and the time-off makes the shutter move more or less against the spring in the IAC. I don't have the circuit diagram here, but usually the engine computer supplies a ground to the to the valve rather than voltage. That is consistent with what you see. When the car is on, the 12V is supplied to one terminal of the IAC. At the other end of the IAC, if the engine is running and everything is working, you should see the pulse train (on and off signals) if you had an oscilloscope. With an averaging multimeter, your meter could read any where from 12Vdc (the computer is dead or the transistor in it is open), to around 1Vdc if the pulse train was 100% on. (1Vdc is the voltage drop of a typical switching transistor.) The 1-9Vdc signal is an attempt by the meter to show the average voltage of a signal that is turning on and off quickly.

As for putting 12Vdc on the shutter, you should see movement, if you have the 12Vdc on the right terminal. If the terminals are switched, the motor is going the wrong way and the shutter won't move.

Also, keep in mind that the IAC is not designed to have 12Vdc applied to it continuously. If you do for any length of time, the motor will burn up.

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