Question about 1999 Jeep Grand Cherokee
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Posted on Jan 02, 2017
According to the fault code, there is no signal from the vehicle speed sensor to the OBD computer. A P1491 code is the radiator fan control circuit. I sounds like you may have an electrical problem that is causing a bunch of false readings. Have the computer reset and try again. You can get all of the fault codes at http://www.wjjeeps.com/faultcodes.htm#0500 Don't forget top rate this solution!!!
Posted on Mar 13, 2009
with an ohm meter check if the wires going to the relay have power when they should. next use a jumper wire from the pos. battery terminal to the power connector on the fan if the fan starts to run off the jumper then its probably the relay to blame. hope this helps.
Posted on Dec 22, 2010
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
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Posted on Dec 20, 2011
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Dec 19, 2011 | 2000 Jeep Grand Cherokee
Oct 15, 2011 | 1999 Jeep Cherokee
Feb 25, 2011 | 2001 Chrysler Voyager
Trouble Code: P1491 You PCM does not sense current to radiator fan when it turns it on. Is the fan coming on or not? Usually not when you have this code. Problem can be with the fuse, relay, wiring or fan itself. First check the fuse. If good, next try swapping the relay with another one in the engine compartment relay box, such as the horn relay.
Let the car warm up and see if the fan will come on. If yes, get a new relay. If not, either use a test light to see if there is voltage at the fan connector when the engine is on and hot, or else test the fan motor by hotwiring it to the battery. If none of this works, please get back to me for how to troubleshoot the wiring.
Radiator Fan Control Relay Circuit Malfunction
Radiator fan control relay circuit is open or shorted to ground Radiator fan control relay circuit is open (test power to IGN) Radiator fan control relay is damaged or has failed PCM has failed
Nov 10, 2010 | 2003 Jeep Grand Cherokee
Nov 02, 2010 | 1999 Jeep Cherokee
Aug 14, 2010 | 1999 Jeep Grand Cherokee
May 04, 2010 | 2000 Jeep Grand Cherokee
Mar 13, 2009 | 2000 Jeep Cherokee
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