fooling the pcm

Here is my problem and any help would be greatly appreciated. I have a 98 jeep tj wrangler with a 99 jeep xj cherokee pcm aka ecu all is good except for i get a check engine light when i turn my a/c on because the cherokee pcm wants to turn on the electric cooling fan "p1491" fault code and my wrangler does not have an electric cooling fan. So as a temporary fix i wired a small light bulb into the pcm plug that wants to turn the fan on, it is a negative wire btw it would go to a relay if it were on a cherokee. So does anyone have any idea what would be an easy fix for this without using a light bulb? i tried to just ground the wire and that works until you turn the a/c off and the pcm thinks that the efan is still running.

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Jody

Wire a relay in place of the bulb, or a resistor instead?

If Ween's suggestion doesn't work, maybe a relay turned on by the aircon (eg, clutch or on switch) which connects that PCM wire to GND.

It may be best using a (say) 47 to 150 Ohm resistor (to GND) assuming that's the resistance of the missing relay or the bulb you used (ie, 2W - 3W).

A few good suggestions. I don't know much about resistors except that they pull a load. How hot would a small resistor get and what size would I need? I also like the idea of wiring it to the a/c relay that wouldn't even be noticeable. How would I get a ground on/off from the a/c relay? Or would I need to install a whole separate relay?

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Jody

Ween's suggestion is best if it is designed for and only senses the presence of a relay (and maybe that it is operating ok), and relays are easier to find & fit than bulbs & resistors.


But otherwise:
If 47R (R = Ohm), P=VV/R = 15x15/47 = 4.7 = 5 Watts.
If 100R, likewise 225/100 = 2.25W => 5W.
If 150, 225/150 = 1.5W. (If 120R; 1.89W)
Hence a 120 Ohm or 150 Ohm 2W resistor.

However you might find it works fine with a 470 Ohm or higher resistance in which case 1/2W is fine.

Use whatever is convenient - a relay coil, bulb, resistor.

well i guess i got lucky today after work i stuck a pin in c-1 connector that tells the a/c to come on and it was negative when the a/c pump came on..YEAH..so i gave it a test and spliced them together. it worked wonderfully. some heat shrink, solder and a little tape all is good. thanks for all the help.

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Jody