Where is the relay located for the code P1491? On a 2000 jeep grand Cherokee?

Hi there:
DTC P1491 - RAD FAN CONTROL RELAY CIRCUIT

DTC P1491 is for the cooling fan relay control circuit as you've found already. Start by checking the fuse for the fan relay. Its in the box under the hood, a 40 amp fuse.

If you've got a couple jumper wires, you can unplug the fan connector and carefully jump the fan to see if it works. The fan connector is on the right side of the back of the fan shroud. Unplug it and jump the black wire to ground and the green to positive. You've got to be very careful doing this though-you are in very tight quarters, its not hard for your jumper wires to touch each other in the connector and short together, and if you use small diameter jumper wires they will get hot quickly when the fan comes on.

If the fan doesn't come on when you jump it, or if it runs slow or sounds bad, you've got a bad motor and will need to replace the fan assembly. One thing that does happen somewhat often, is a bad fan motor will burn up the relay. If the fan motor is drawing too much current it will overload the relay and burn it up. This is why its so important that if the fan motor runs slow or makes noise that you replace it, or you may end up burning up relays frequently.

If the fan runs and the fuse is good, its very likely you just need a fan relay. This is a pulse width modulated relay, not the on/off clicker type you'd find in the fuse box. This unit is capable of infinite speed control. It gets very hot in operation, so its mounted to the body sheet metal to allow heat to dissipate through the sheet metal. The relay is mounted under the right headlamp held down with two 8mm screws. To get to it you have to remove the front bumper cover and headlamp bracketry to access the relay. These relays are pretty common.

Check and test this possible causes:
radiator fan ctrl rly circuit wire harn intermittent defect
radiator fan ctrl rly circuit wire harn observable defect
radiator fan relay ground circuit open
rad fan relay control circuit open
radiator fan relay control circuit short to ground
rad fan control relay defective
PCM defective

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Remove the right headlight and cut a hole into the plastic cover over the bumper your sencer is there.this is the quick fix or pay 2-3 hundred to have replaced