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Old July 11th, 2010, 18:25
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CharlesS CharlesS is offline
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Join Date: Mar 2003
Location: Quezon Province, Philippines
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Re: Radiator Fan Override Switch (The Easy Way)

Originally Posted by kastein View Post
My info says this is wrong, extended idle is just a switch that grounds a pin on the ECU when the switch is turned on. The ECU uses this to change its idle RPM setpoint from 750 to 1000 and turn the fan on when required. Covered in section 14 and wiring schematic on page 8W-14, at least in the '98 FSM. If you ground pin A12 in C1 (connector 1) of the ECU wiring harness on any 4.0L XJ this should be enabled.
OK.... I have the same info in my '98 FSM.
I was just using that explanation as an example...

This idea of grounding out an ECU terminal is the wrong approach to manually turn the fan on....
The research (almost 7 years ago) I referenced in an earlier post showed this to be a mistake that could harm the ECU...
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