Currently Im using a single 25ohm, 5 watt resistor in place of a solenoid to prevent my cars computer (PCM) from throwing a code. This is part of a project Ive been working on. The size of this resistor is rediculous and Id like to know if I could use five 5ohm, 1 watt resistors in series to reduce the size of the project board. Any help appreciated!

 

I think that five 1W resistors take up more space than a single 5W resistor.
Do it if you want but make sure there is sufficient free flowing air to cool them.

The heater for the O2 sensor that you removed?

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Uncle $crooge

 

How 'bout a 12v lamp, 1/2 amp?

 

That resistor might overheat 12²/25 = 5.76W.

You could use a 30R assuming it will draw enough current to keep the ECU happy.

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maybe there is a better way of doing this....a little background about this part of the project. There are 2 solenoids in my transmission. I have the dealer manuals which state the computer throws a code if either one is not within a range of 20-40 ohms. The solenoid is connected to 12 vdc and gets its ground to operate from the computer. So, what do you guys think the computer is looking for? A lower voltage within a range that would correspond to the resistance of each solenoid? If so, wouldn't it be easier (and a whole lot smaller) to simply supply a voltage within that range through a smaller resistor? Just an idea but I don't have the electronic math know how to figure that out.

That brings me to another topic...What would you guys suggest for learning the math? I mean Id like to not have to rely on the members here so much to figure out what resistors I need to saturate this transistor and so forth...not that I mind the help but Id like to try and figure it out on my own first.

Anyway back on topic. I was also thinking of a way to use a single resistor to supply the "signal" to both solenoid channels of the computer...once again Im not sure how to figure that value out but I recall someone saying it would be half the resistance or something to that effect. I would really appreciate any help and as always THANK YOU...your help is invaluable to all of us who know so little

 

Are the solenoids still there and the coils not as low a value as the ECU needs? If so parallel a resistor with the coil? Does the solenoid work but just out of range for the ECU?

Google for ohm's law for a start on the math part.

 

solenoids are still there and work/read correctly. I built a project to control the shifts manually by reading a valve position switch in the transmission which the project reads as a specific gear and energizes the solenoids in the correct order. Im currently using 2 dpdt relays...one switches the solenoids between computer control and my manual control project and the other connects these two resistors (dummy solenoids) to the computer so it doesnt go crazy when Im manually controlling the solenoids.