OK - I am not a Jeep owner, but yet a customer of mine is and he is having some issues with his Cherokee. He is getting a MIL (P1491 - Rad fan control relay circuit). I have gone though this website -

http://www.lunghd.com/Tech_Articles/..._Diagnosis.htm

Which I got off these forums. Everything has been EXTREMLY Helpful, with 1 exception. I have made it though all the trouble shooting steps and got to this step:

Check for battery voltage at terminal 2 of the fan relay connector (Fig. 43). If battery voltage is not present replace the fan diode assembly.

There is no voltage at this terminal - I started to cheer! Then went to find the Fan Diode Assembly and about 2 hours later, and alot of web searchs I can not find anything that points me in the right direction. I did find a Diode like device right next to the fuse box under the hood on the passenger side of the vehicle. Just not sure if this is the correct one or if this is for something else. There is 3 wires going into this Diode like plug. So I am not sure if this is correct or not. So I am reaching out to see if anyone out here can help me out here.

Vehicle Information -
1999 Jeep Cherokee Sport
4.0L - AUTO
AC
4x4

Look forward to the responses!

 

Anyone?

 

I don't see a year listed on your diagram fig. 42. Are you sure it's the same? The diode is used for fan operation from either
1. A/C On
or
2. Engine cooling switch closed demanding cooling.

If that is the right diagram did you look at the harness drivers side front for the two wires, orange/white tracer, gray/white tracer? (could be taped up in the harness)

 

I am not 100% certain that this is the correct wire diagram for the 1999 Jeep. The troubleshooting was right on point as to what I got for results. Just now down to this fan diode assembly that I am unable to locate.

 

There IS a box hooked up inline with fan-has positive and negative in and then out to the fan, but I believe it is not a diode, but a "soft start" module for the fan, in other words, the voltage goes in, but does not let full voltage in to the fan immediately.
If you notice on the newer ones ('97 +), the fan speeds up gradually, instead of immediately slaqmming on full speed.
If you remove this module, the fan kicks on full speed, instead of gradually ramping up.
Thias module has one end that plugs into the fan, and the other end has the same plug as the fan to plug into the wiring haness.

Nick

 

Hi i have 1999 grand cherokee the ryley daiod is on pasynger side under headlight .remov the headlight and you haveto cut hole to get to it.Dodge neon uses identycol ryley is loceyted dryver front side you can lokeyted from under the car behaind headlight on the fender side .hope thys wyll helpyou.